**File Specification for GEOS-5 MERRA Reanalysis Gridded Output**

*Global Modeling and Assimilation Office*

*Goddard Space Flight Center, Greenbelt, Maryland*

http://gmao.gsfc.nasa.gov

Release Date: tbd

Version 1.0

Latest Revisions: 12/19/2007 6:21:00 PM

Document maintained by Rob Lucchesi (GMAO, SAIC)

*Permission to quote from this document should be obtained from the
GMAO.*

![](media/image1.png){width="0.5979166666666667in"
height="0.5180555555555556in"}

**Michele Rienecker**

**Global Modeling and Assimilation Office**

**Earth Sciences Division**

**NASA Goddard Space Flight Center**

**Greenbelt, Maryland 20771**

This page intentionally left blank.

**File Specification for GEOS-5 MERRA Reanalysis Gridded Output**

**Document No. GMAO-100XvX.0**

**September 21, 2006**

Approved by:

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

Michele Rienecker Date Gi-Kong Kim Date

Head CCB Chair

Global Modeling and Assimilation Office Global Modeling and Assimilation
Office

Code 610.1, NASA GSFC Code 610.2, NASA GSFC

**REVISION HISTORY**

  ------------------------------------------------------------------------
  **Version    **Revision    **Extent of Changes**           **Approval
  Number**     Date**                                        Authority**
  ------------ ------------- ------------------------------- -------------
  1.0          03/24/2006    Baseline                        

  2.0          04/19/2007    First version posted for        
                             comment on MERRA web site.      

  2.1          Xx/xx/2007                                    
  ------------------------------------------------------------------------

1\. Introduction 3

2\. Format and File Organization 4

2.1 Dimensions 5

2.2 Variables 6

2.3 Global Attributes 7

ArchivedMetadata.0 character The ECS archive metadata. 8

3\. Instantaneous vs Time-averaged Products 8

4\. Grid Structure 8

4.1 Horizontal Structure 8

4.2 Vertical Structure 9

5\. File Naming Conventions 11

5.1 File Names 11

5.2 Earth Science Data Types (ESDT) Name 14

6\. Summary of MERRA file collections 15

7\. Metadata 17

7.1 EOSDIS Metadata 17

7.2 CF Metadata 17

8\. Sample Software 18

8.1 HDF-EOS Example 18

8.2 HDF (non EOS) Example 20

Appendix A: The IAU procedure 24

Appendix B: Observational Inputs to MERRA 25

Appendix C: Collection Metadata 29

Appendix D: Vertical Structure 32

Appendix E: GEOS-5 data collections 33

E.1 Time-independent Variables 33

const_2d_asm_Nx 33

E.2 Analysis Files 34

inst6_3d_ana_Nv 34

inst6_3d_ana_Np 35

E.3 History Files 36

inst3_3d_asm_Cp 36

tavg3_3d_cld_Cp 37

tavg3_3d_mst_Cp 38

tavg3_3d_rad_Cp 39

tavg3_3d_trb_Cp 40

tavg3_3d_tdt_Cp 41

tavg3_3d_udt_Cp 42

tavg3_3d_qdt_Cp 43

tavg3_3d_odt_Cp 44

tavg1_2d_slv_Nx 45

tavg1_2d_flx_Nx 47

tavg1_2d_rad_Nx 49

tavg1_2d_lnd_Nx 51

tavg1_2d_int_Nx 53

E.4 Chemistry Forcing Files 55

const_2d_chm_Fx 55

tavg3_3d_chm_Fv 56

tavg3_3d_chm_Fe 57

tavg3_2d_chm_Fx 58

tavg3_3d_chm_Nv 59

tavg3_3d_chm_Ne 60

inst_3d_chm_Ne 61

Appendix F: Detailed Description of Output Variables 62

F.1 Three-dimensional Fields 62

F.2 Two-dimensional Fields 66

Appendix G: Surface Representation 70

References 72

Web Resources 73

# 1. Introduction 

The Modern Era Retrospective-analysis for Research and Applications
(MERRA) is a NASA reanalysis for the satellite era using a major new
version of the Goddard Earth Observing System Data Assimilation System
Version 5 (GEOS-5). MERRA focuses on historical analyses of the
hydrological cycle on a broad range of weather and climate time scales
and places the NASA EOS suite of observations in a climate context. It
is one of NASA's deliverables for the Climate Change Science Program
(CCSP). MERRA covers the period 1979-2007, with plans to extend the
analysis forward in time as resources allow.

MERRA uses the GEOS-5 Data Assimilation System (GEOS-5 DAS), which
represents a radical evolution of the system, with the adoption of a
joint analysis with the National Centers for Environmental Prediction
(NCEP) and of a new set of physics packages for the atmospheric general
circulation model (AGCM). The first choice allows the Global Modeling
and Assimilation Office (GMAO) to take advantage of the developments,
especially that of radiance assimilation, at NCEP and the Joint Center
for Satellite Data Assimilation (JCSDA), and facilitates our own
contributions to the operational system. The second choice allows us to
tune the system for both weather and climate applications and to enhance
the usefulness of satellite observations.

The new GEOS-5 AGCM uses the finite-volume dynamics (Lin, 2004)
integrated with various physics packages under the Earth System Modeling
Framework (ESMF) (e.g., Collins et al., 2005) including the Catchment
Land Surface Model (CLSM) (e.g., Koster et al., 2000). The GSI analysis
is a new three-dimensional variational (3DVar) analysis applied in
grid-point space to facilitate the implementation of anisotropic,
inhomogeneous covariances (e.g., Wu et al., 2002; Derber et al., 2003).
In contrast, in the Spectral Statistical Interpolation (SSI) analysis,
used for the NCEP/NCAR Reanalyses, the background error covariances were
defined spectrally and were nearly homogeneous around a latitude band.
The GSI implementation incorporates a set of recursive filters that
produce approximately Gaussian smoothing kernels and isotropic
correlation functions. By superposition of Gaussian kernels with
different length scales it is possible to generate non-Gaussian shapes,
and generally to implement a large class of flow-dependent inhomogeneous
background error covariance models (Purser et al., 2003a, b).

The GEOS-5 DAS is a marked change from the GEOS-4 DAS which was based on
the Physical-space Statistical Analysis System (PSAS) coupled to the
GEOS-4 model. The GEOS-4 system is documented in Bloom et al. (2005).
Like GEOS-5, GEOS-4 used the finite-volume dynamical core, but
integrated in version 3 of the Community Climate Model (CCM3) and
version two of the Community Land Model (CLM2). PSAS assimilated
retrievals of satellite data, not radiances, and the analysis was a
height-wind analysis. Like GEOS-5, the background error covariance
functions were in grid-point space, but were horizontally-isotropic,
compactly-supported spline functions. The GEOS-4 system assimilated
roughly 10^5^ observations per analysis time whereas the GEOS-5 system
assimilates over an order of magnitude more -- roughly 2 × 10^6^
observations are actively assimilated each analysis, including about 7.5
× 10^5^ AIRS radiance data. The input stream is roughly twice this
volume, but because of the large volume, the data are thinned
commensurate with the analysis grid to reduce the computational burden.
Data are also rejected from the analysis through quality control
procedures designed to detect, for example, the presence of cloud.

To minimize the spurious periodic perturbations of the analysis, MERRA
uses the Incremental Analysis Update (IAU) technique developed by Bloom
et al. (1996). More details of this procedure are given in [Appendix
A](#_Appendix_A:_The).

The version of the DAS used for MERRA is GEOS-5.1.1.

Observations used for MERRA are summarized in [Appendix
B](#_Appendix_B:_Observational). The data streams assimilated by the
GEOS-5 DAS for MERRA are shown in Table B.1; their availability and the
source of the data assimilated for MERRA are shown in Table B.2.

The analysis is performed at a horizontal resolution of 2/3 degrees
longitude by ½ degree latitude and at 72 levels, extending to 0.01 hPa.
Some products, such as the instantaneous analysis fields, are available
on the native three-dimensional grid. Hourly two-dimensional diagnostic
fields are also available at the native horizontal resolution. Other
products are available on a coarser horizontal grid with resolution of
1.25 ×1.25 degrees or 1 × 1.25 degrees, the latter for use by the
chemistry transport community. These may be on the model's native
vertical grid or at 42 pressure surfaces extending to 0.1 hPa. Surface
data, near surface meteorology, selected upper-air levels, and
vertically integrated fluxes and budgets are produced at one-hour
intervals, which will help the development of offline land and ocean
models and data assimilation systems by resolving the diurnal cycle.
Monthly mean versions of most of these products will also be available.

This document describes the gridded output files produced by the MERRA
reanalysis. These are considerably different from the operational GEOS-5
DAS output. The MERRA data will be available online through the Goddard
Earth Sciences (GES) Data and Information Services Center DISC). The
disk cache and interface tools in this Modeling DISC (MDISC) system
leverage new DISC capabilities in serving active data archives. More
information can be found at
[http://mdisc.sci.gsfc.nasa.gov](http://mdisc.sci.gsfc.nasa.gov/).
Detailed documentation of the data access procedures can be found at
[http://gmao.gsfc.nasa.gov.](http://gmao.gsfc.nasa.gov./)

# 2. Format and File Organization 

GEOS-5 files are in HDF-EOS format, which is an extension of the
Hierarchical Data Format Version 4 (HDF-4), developed at the National
Center for Supercomputing Applications <http://www.hdfgroup.org/>.
HDF-EOS provides additional capabilities over HDF-4, but does not
prevent the use of the files as standard HDF-4 files.

Each GEOS-5 file will contain a single HDF-EOS grid, which in turn
contains a number of geophysical quantities that we will refer to as
"fields" or "variables." Some files will contain 2-D variables on a
longitude-latitude grid, and some files will contain 3-D variables, or a
mixture of 2-D and 3-D variables on the same longitude-latitude grid,
but with a vertical dimension applicable to all the 3D variables.

The variables are created using the **GDdeffield** function from the
HDF-EOS GD (GriD) API, which stores them as HDF Scientific Data Set
(SDS) arrays, so that they can be read with standard HDF routines. In
addition to the geophysical variables, the files will have SDS arrays
that define dimension scales (or coordinate variables). There will be
two distinct scales for each dimension, which will ensure that a wide
variety of graphical display tools can interpret the data. In
particular, there are dimension scales that adhere to the [CF](#CF)
conventions, as well as ones that adhere to the [COARDS](#COARDS)
conventions.

Due to the size of the MERRA archive, all data will be compressed with a
GRIB-like method that is invisible to the user. This method does degrade
the precision of the data, but every effort has been made to ensure that
differences between the product and the original, uncompressed data are
not scientifically meaningful. Once the precision has been degraded, the
files are written using the standard gzip deflation available in HDF-4.

EOS Core System (ECS) metadata and other information will be stored as
global attributes.

## 

## 2.1 Dimensions 

GMAO HDF-EOS files will contain two sets of dimension scale (coordinate)
information. One set of dimensions is defined using the
**SDsetdimscale** function of the standard HDF SD interface. This set of
scales will have an attribute named "units," set to an appropriate
string defined by the CF and COARDS conventions that can be used by
applications to identify the dimension. The other set of dimension
scales is created using the **GDdeffield/GDwritefield** functions.

Table 2.1-1. Dimension Variables Contained in GMAO HDF-EOS Files

+--------------+---------------------+-------+-----------------------+
| **Name**     | **Description**     | **T   | ***units* attribute** |
|              |                     | ype** |                       |
+--------------+---------------------+-------+-----------------------+
| XDim:EOSGRID | Longitude           | fl    | degrees_east          |
|              |                     | oat32 |                       |
+--------------+---------------------+-------+-----------------------+
| YDim:EOSGRID | Latitude            | fl    | degrees_north         |
|              |                     | oat32 |                       |
+--------------+---------------------+-------+-----------------------+
| Hei          | pressure or layer   | fl    | hPa or layer          |
| ght:EOSGRID\ | index               | oat32 |                       |
| (3D only)    |                     |       |                       |
+--------------+---------------------+-------+-----------------------+
| TIME:EOSGRID | minutes since first | fl    | minutes               |
|              | time in file        | oat32 |                       |
+--------------+---------------------+-------+-----------------------+
| XDim         | Longitude, in       | fl    | N/A                   |
|              | degrees east        | oat64 |                       |
+--------------+---------------------+-------+-----------------------+
| YDim         | Latitude, in        | fl    | N/A                   |
|              | degrees north       | oat64 |                       |
+--------------+---------------------+-------+-----------------------+
| Height (3D   | pressure or level   | fl    | N/A                   |
| only)        | indices             | oat64 |                       |
+--------------+---------------------+-------+-----------------------+
| Time         | seconds since       | fl    | N/A                   |
|              | 00:00Z on           | oat64 |                       |
|              |                     |       |                       |
|              | 1 January 1993      |       |                       |
+--------------+---------------------+-------+-----------------------+

The 32-bit dimension variables have a \"units\" attribute that makes
them COARDS-compliant, while the 64-bit dimension variables satisfy ECS
requirements.

## 2.2 Variables 

Variables are stored as SDS arrays, even though they are defined with
the HDF-EOS **GDdeffield** function. As a result, one can use the SD
interface of the HDF library to read any variable from the file. The
only thing one must know is the sds variable name or *short name* of the
variable and the number of dimensions (the rank). You can quickly list
the variables in the file by using common utilities such as *ncdump* or
*hdp*. Both utilities are distributed from NCSA with the HDF library. In
[Section 8](#sample-software) we will present sample code for reading
one or more data fields from this file. The *short names* for all
variables in all GMAO data products are listed in [Appendix
E](#_Appendix_E:_GEOS-5). A glossary with a brief description of each
variable is given in [Appendix F](#_Appendix_F:_Detailed).

Each variable will have several useful metadata attributes. Many of
these attributes are required by the [CF](#CF) and [COARDS](#COARDS)
conventions, while others are specific for GMAO products. The following
table lists required attributes. Other attributes may be included for
internal GMAO use and can be ignored.

Table 2.2-1 Metadata attributes associated with each SDS.

  -------------------------------------------------------------------------------
  **Name**        **Type**[]{#FillValue   **Description**
                  .anchor}                
  --------------- ----------------------- ---------------------------------------
  \_FillValue     float32                 Floating-point value used to identify
                                          missing data. Will normally be set to
                                          1e15. Required by CF.

  missing_value   float32                 Same as \_FillValue. Required for
                                          COARDS backwards compatibility.

  valid_range     float32, array(2)       This attribute defines the valid range
                                          of the variable. The first element is
                                          the smallest valid value and the second
                                          element is the largest valid value.
                                          Required by CF. missing_value

  long_name       String                  Ad hoc description of the variable.
                                          Required by COARDS.

  standard_name   String                  Standard description of the variable as
                                          defined in CF conventions. (See
                                          References).

  units           String                  The units of the variable. Must be a
                                          string that can be recognized by
                                          UNIDATA\'s Udunits package.

  scale_factor    float32                 If variable is packed as 16-bit
                                          integers, this is the scale_factor for
                                          expanding to floating-point. Currently
                                          we do not plan to pack data, thus value
                                          will be 1.0 units

  add_offset      float32                 If variable is packed as 16-bit
                                          integers, this is the offset for
                                          expanding to floating-point. Currently,
                                          we do no plan to pack data, thus value
                                          will be 0.0.
  -------------------------------------------------------------------------------

## 2.3 Global Attributes 

In addition to SDS arrays containing variables and dimension scales,
global metadata is also stored in GMAO HDF-EOS files. Some metadata are
required by the CF/COARDS conventions, some are present to meet ECS
requirements, and others as a convenience to users of GMAO products. A
summary of global attributes present in all MERRA files is shown in
Table 2.3-1.

Table 2.3-1 Global metadata attributes associated with each SDS.

  --------------------------------------------------------------------------
  **Name**             **Type**      **Description**
  -------------------- ------------- ---------------------------------------
  Conventions          character     Identification of the file convention
                                     used, currently "CF-1.0"

  title                character     Experiment identification: "MERRA"

  history              character     CVS tag of this release. CVS tags are
                                     used internally by the GMAO to
                                     designate versions of the system.

  institution          character     "NASA Global Modeling and Assimilation
                                     Office"

  source               character     CFIO Version (CFIO is the GMAO's IO
                                     layer)

  references           character     GMAO website address

  comment              character     As required

  HDFEOSVersion        character     Version of the HDF-EOS library used to
                                     create this file.

  StructMetadata.0     character     This is the GridStructure metadata that
                                     is created by the HDF-EOS library.

  CoreMetadata.0       character     The ECS inventory metadata.

  ArchivedMetadata.0   character     The ECS archive metadata
  --------------------------------------------------------------------------

#  

# 3. Instantaneous vs Time-averaged Products 

Each file collection listed in [Section
6](#summary-of-merra-file-collections) contains either instantaneous or
time-averaged products, but not both.

All instantaneous collections contain fields at *synoptic times* (00
GMT, 06 GMT, 12 GMT, and 18 GMT). In addition, three-hourly
instantaneous collections also include snapshots at *mid-synoptic times*
(03 GMT, 09 GMT, 15 GMT, and 21 GMT). 

Time-averaged collections may contain either hourly, three-hourly,
monthly, or seasonal means, but not mixtures of these. Each
time-averaged collection consists of a continuous sequence of data
averaged over the indicated interval and time stamped with the central
time of the interval. For hourly data, for example, these times are
00:30 GMT, 01:30 GMT, 02:30 GMT, etc.. Only products consisting
exclusively of two-dimensional (horizontal) fields are produced hourly.
Three-hourly time-averaged files contain averages over time intervals
centered and time stamped at 01:30 GMT, 04:30 GMT, 07:30 GMT, and so on.
Monthly files represent averages for the calendar months, accounting for
leap years. For monthly means, each file contains a single month.

Each hourly, three-hourly, or six-hourly collection, whether
instantaneous or time-averaged, consist of a set of daily files, with
the date as part of the [filename](#file-names). For collections of
monthly or seasonal means each month or season is in a separate file,
and file names are also include a date in the file name.

#  

# 4. Grid Structure 

## 4.1 Horizontal Structure 

Fields will be produced on three different horizontal grids: the a
native grid of the Finite-Volume dynamical core, with a resolution of
2/3 longitude by 1/2 degree latitude, a coarse version of the FV grid,
with a resolution of 1.25 longitude by 1 degree latitude, and a uniform
coarse grid, with a resolution of 1.25 by 1.25 degrees.

[]{#Native .anchor}GEOS-5 ***native resolution*** gridded output is on a
global horizontal grid, consisting of **IMn=540** points in the
longitudinal direction and **JMn=361** points in the latitudinal
direction. The horizontal native grid origin, associated with variables
indexed (*i=*1*, j=*1) represents a grid point located at (180W, 90S).
Latitude and longitude of grid points as a function of their indices
(*i, j*) can be determined by:

$$\begin{array}{r}
\lambda_{i} = - \text{180} + (\Delta\lambda)_{n}(i - 1),\text{   }i = 1,\text{IMn} \\
\phi_{j} = - \text{90} + (\Delta\phi)n(j - 1),\text{    }j = 1,\text{JMn}
\end{array}$$

Where $(\Delta\lambda)_{n}$=2/3 o and $(Dj)_{n}$ = 1/2o. For example,
(*i* = 271, *j* = 181) corresponds to a grid point at
($\lambda = 0,j = 0$).

[]{#FVCoarse .anchor}FV ***reduced resolution*** gridded output is used
only for the specialized chemistry forcing files (see [Appendix
E](#_Appendix_E%3A_GEOS-5_data_collections)). It is on a global
horizontal grid, consisting of **IMf=288** points in the longitudinal
direction and **JMf=181** points in the latitudinal direction. The
horizontal native grid origin, associated with variables indexed
(*i=*1*,j=*1) represents a grid point located at (180W, 90S). Latitude
and longitude of grid points as a function of their indices (*i, j*) can
be determined by:

$$\begin{array}{r}
\lambda_{i} = - \text{180} + (\Delta\lambda)_{f}(i - 1),\text{   }i = 1,\text{IMf} \\
\phi_{j} = - \text{90} + (\Delta\phi)_{f}(j - 1),\text{    }j = 1,\text{JMf}
\end{array}$$

where $(\Delta\lambda)_{f}$ = 1.25ο and $(\Delta\phi)_{f}$ = 1o.

[]{#Coarse .anchor}MERRA ***reduced resolution*** gridded output is on a
global horizontal grid consisting of **IMc=288** points in the
longitudinal direction and **JMc=144** points in the latitudinal
direction. The horizontal coarse grid origin, associated with variables
indexed (*i=*1*, j=*1), represents a grid point at (179.375W, 80.375S),
so that the Dateline and the South Pole are "edges" of the first grid
box. Latitude and longitude as a function of their indices (*i, j*) for
the coarse grid can be determined by:

$$\begin{array}{r}
\lambda_{i}\text{=-}\text{180} + (D\lambda)_{c}(i - 1),\text{   }i = 1,\text{IMc} \\
j_{j}\text{=-}\text{90} + (Dj)_{c}(j - 1),\text{    }j = 1,\text{JMc}
\end{array}$$

where $(D\lambda)_{c}$= $(Dj)_{c}$=1.25o.

## 4.2 Vertical Structure 

Gridded products will use four different vertical configurations:
Horizontal-only (can be vertical averages, single level, or surface
values), pressure-level, model-level, or model-edge. Horizontal-only
data for a given variable appear as 3-dimensional fields (x, y, time),
where multiple times can span multiple files, while pressure-level,
model-level, or model-edge data appear as 4-dimensional fields (x, y, z,
time). Pressure-level data will be output on the **LMp=42** pressure
levels shown in [Appendix D](#_Appendix_D:_Vertical) . The GEOS-5 model
layers used for MERRA output are on a terrain-following hybrid sigma-p
coordinate. Model-level data will be output on the **LM=72** layers
shown in [Appendix D](#_Appendix_D%3A_Vertical_Structure). The
model-edge products contain fields with **LMe = LM + 1** levels
representing the layer edges. Model-level files will contain the
LM-layer 3D variable ([DELP](#DELP)**ijl**), the pressure thickness for
each layer, as well as the surface pressure (PS**ij**). The pressure at
the model top is a fixed constant, **PTOP=0.01 hPa**. Pressures at model
edges should be computed by summing the DELP starting at PTOP. A
representative pressure for the layer can then be obtained from these.
In the GEOS-4 *eta* files, one could compute the pressure on the edges
by using the "ak" and "bk" values and the surface pressure. In GEOS-5,
the full 3-dimensional pressure variables are explicitly provided
through ([DELP](#DELP)**ijl**), PTOP, and (PS**ij**). For the MERRA
products documented here, all model-level fields are on a hybrid-sigma
coordinate, and their vertical location could be obtained from the
"ak-bk" relationship as well. But this may change in future GMAO
systems. We thus recommend that users rely on the reported 3D pressure
distribution, and not use ones computed from the "ak" and "bk".

Figure 1 is a schematic (not to scale) of the GEOS-5 vertical coordinate
system. Note that the indexing in the vertical is top to bottom, i.e.,
layer 1 is the top layer of the atmosphere, while layer [LM](#LM) is
adjacent to the earth's surface. The same is true for edge variables,
with level 1 being the top of the model's atmosphere (PTOP), and level
LM+1 being the surface.

# 5. File Naming Conventions 

Each GEOS-5 product file will have a complete file name identified in
the EOSDIS metadata as \"LocalGranuleID\". EOSDIS also requires
eight-character abbreviated naming indices for each Earth Science Data
Type (ESDT). In MERRA each file collection has a unique ESDT index. The
ESDT index convention is described in section 5.2.

## 5.1 File Names

The standard full name for the assimilated GEOS-5 MERRA products will
consist of five dot-delimited nodes:

***runid*.*runtype.config.collection.timestamp***

The node fields, which vary from file to file, are defined as follows:

> ***runid***
>
> All MERRA runs will be identified by **MERRA**SVv , where the numeric
> qualifiers S and Vv denote the production *Stream* and the *Version*
> numbers.
>
> MERRA will be run in three production *Streams*, each covering
> approximately a third of the MERRA period, plus overlaps and spin-up
> periods. If the stream number is not applicable (the case for
> ancillary products, such as forecasts), *S* is set to 0, otherwise it
> is 1, 2, or 3.
>
> The *Version* numbers are non-zero when there is more than one version
> of the dataset. It is usually zero, denoting the original processing.
> MERRA will be conducted with a frozen assimilation system, so there
> should be no updates or patches to the GEOS-5 software. Version
> changes indicate either that a problem was encountered after product
> release and a reprocessing was necessary (v), or a period was
> reprocessed with a modified version of the system for scientific
> studies (V). For any such reprocessing, we will increment the version
> number appropriately and this will be documented in the metadata
> parameter "history." Information on version differences will also be
> available at the MERRA web site
> ([http://gmao.gsfc.nasa.gov/research/merra](http://gmao.gsfc.nasa.gov/research/merra/)/).
>
> ***runtype*:**
>
> The main GEOS-5 MERRA products will be from standard production
> (**prod**) runs. Products from other runs or run segments may be made
> available for specialized analyses.
>
> **prod**   - Standard product
>
> **ovlp**  - Overlap product
>
> **spnp** - Spin-up product
>
> **swep** -- Sweeper/Scout product
>
> **rosb**  - Reduced observing system product
>
> **cers**  - CERES observing system product
>
> ***config*:**
>
> The GEOS-5 analysis and forecast system can run in different
> configurations.
>
> **assim** -- Assimilation. Uses a combination of atmospheric data
> analysis and model forecasting to generate a time-series of global
> atmospheric quantities.
>
> **simul** -- Simulation. Uses a free-running atmospheric model with
> some prescribed external forcing, such as sea-surface temperatures.
>
> **frcst** -- Forecasts. Uses a free-running atmospheric model
> initialized from an analyzed state.
>
> The main configuration used to support MERRA will be assimilation
> (**assim**). A long, AMIP-style simulation will also be performed and
> it will be labeled **simul**.
>
> ***collection*:**
>
> All MERRA data are organized into file *collections* that contain
> fields with common characteristics. These collections are used to make
> the data more accessible for specific purposes. Fields may appear in
> more than one collection. Collection names are of the form
> *freq_dims_group_HV*, where the four attributes are:
>
> *freq:* time-independent (**cnst**), instantaneous (**inst*F*),** or
> time-average (**tavg*F***), where ***F*** indicates the frequency or
> averaging interval and can be any of the following:
>
> **1** = Hourly
>
> **3** = 3-Hourly
>
> **6** = 6-Hourly
>
> **D** = Daily
>
> **M** = Monthly (**tavg** only)
>
> **U** = Monthly-Diurnal (**tavg** only)
>
> **S** = Seasonal (**tavg** only)
>
> **A** = Annual (**tavg** only)
>
> **0 =** Not Applicable
>
> *dims:* **2d** for collections with only 2-dimensional fields or
> **3d** for collections with a mix of 2- and 3-dimensional fields.
>
> *group:* A three-letter mnemonic for the type of fields in the
> collection. It is a lowercase version of the group designation used in
> the ESDT name, as [listed in the next section](#Group).
>
> *HV*: Horizontal and Vertical grid.
>
> *H* can be:
>
> **N**: Native (2/3 x ½) horizontal resolution
>
> **C**: Reduced (1.25 x 1.25) horizontal resolution
>
> **F**: Reduced FV (1.25 x 1) horizontal resolution
>
> *V* can be:
>
> **x**: horizontal-only data (surface, single level, etc.) ; *dims*
> must be **2D**
>
> **p**: pressure-level data (see [Appendix
> D](#_Appendix_D%3A_Vertical_Structure) for levels) ; *dims* must be
> **3D**
>
> **v**: model layer centers (see Appendix D ) *dims* must be **3D**
>
> **e**: model layer edges (see Appendix D ) *dims* must be **3D**
>
> ***timestamp:***
>
> This node defines the date and time associated with the data in the
> file. It has the form *yyyymmdd* for either instantaneous or
> time-averaged daily files, *yyyymm* for monthly-mean files, or
> *yyyysss* for seasonal-mean files*.*
>
> **yyyy** - year string (e.g. , \"2002\")
>
> **mm** - month string (e.g.., \"09\" for September)
>
> **dd** - day of the month string (optional)
>
> **sss** - season (e.g., DJF) (optional)

***EXAMPLE***:

**MERRA300.prod.assim.tavg3_3d_tdt_Cp.20020915.hdf**

This is an example of a MERRA filename from the production segment of
the original version of the third (most recent) assimilation stream. The
data are time-averaged, three-dimensional, temperature tendency
products, at reduced horizontal resolution, interpolated to pressure
levels. The file contains all data for 15 September 2002.

## 5.2 Earth Science Data Types (ESDT) Name 

To accommodate EOSDIS toolkit requirements, all MERRA files are
associated with an eight-character ESDT. The ESDT is a short (and rather
cryptic) handle for users to access sets of files. In MERRA the ESDT
will be used to identify *collections* and will consist of a compressed
version of the collection name of the form:

*CTFHVGGG\
*

where

> *C*: Configuration
>
> **A** = Assimilation
>
> **F =** Forecast
>
> **S =** Simulation
>
> *T*: Time Description:
>
> **I** = Instantaneous
>
> **T =** Time-averaged
>
> **C** = Time-independent
>
> *F*: Frequency
>
> **1** = Hourly
>
> **3** = 3-Hourly
>
> **6** = 6-Hourly
>
> **D** = Daily
>
> **M** = Monthly
>
> **S** = Seasonal
>
> **A** = Annual
>
> **0 =** Not Applicable
>
> *H*: Horizontal Resolution
>
> **N** = [Native](#Native).
>
> **F =** [Reduced resolution version of model grid](#FVCoarse)
>
> **C =** [Reduced resolution](#Coarse)
>
> *V*: Vertical Location
>
> **X** = Two-dimensional
>
> **P** = Pressure
>
> **V =** model layer center
>
> **E** = model layer edge
>
> []{#Group .anchor}*GGG*: Group
>
> **ANA** = direct analysis products
>
> **ASM** = assimilated state variables (from the IAU corrector, see
> [Appendix A](#_Appendix_A:_The))
>
> **TDT =** tendencies of temperature
>
> **UDT =** tendencies of eastward and northward wind components
>
> **QDT =** tendencies of specific humidity
>
> **ODT =** tendencies of ozone
>
> **LND** = land surface variables
>
> **FLX =** surface turbulent fluxes and related quantities
>
> **OCN** = ocean surface variables
>
> **MST** = moist processes
>
> **CLD** = clouds
>
> **RAD =** radiation
>
> **TRB =** turbulence
>
> **SLV** = single level
>
> **INT** = vertical integrals

**CHM =** chemistry forcing

#  

# 6. Summary of MERRA file collections

The GEOS-5 MERRA product is organized into the 24 collections listed in
Tables 6.1 and 6.2. These are described in detail in [Appendix
E](#_Appendix_E:_GEOS-5_1). The 17 collection in Table 6-1 are the
"standard" product intended for most diagnostic work. The seven
"chemistry" collections in table 6-2 are more specialized products,
intended for forcing off-line chemistry transport models (CTMs). The
last three of these, in particular, are for CTMs using the GEOS-5
transport cores.

Collection names follow the conventions described in [Section
5](#file-naming-conventions). Sizes are given in Gbytes/day and Tbytes
for the entire collection. Numbers in parentheses are estimates for the
corresponding compressed file.

Table 6-1 List of standard collections

  -----------------------------------------------------------------------------------------------------------------
  **Name**                                          **Description**                          **Size Gbytes/day //
                                                                                             Tbytes**
  ------------------------------------------------- ---------------------------------------- ----------------------
  [const_2d_asm_Nx](#_5._File_Naming_Conventions)   Constant fields                          

  [inst6_3d_ana_Nv](#Xana)                          Analyzed fields on [model                1.347 (0.455) // 14.8
                                                    layers](#Elevs)                          (5.0)

  [inst6_3d_ana_Np](#Xanap)                         Analyzed fields at [pressure             0.792 (0.290) // 8.71
                                                    levels](#_5._File_Naming_Conventions)    (3.2)

  [inst3_3d_asm_Cp](#Xasm)                          Basic assimilated fields from            0.616 (x.xxx)
                                                    [IAU](#_Appendix_A:_The_IAU_procedure)   
                                                    corrector                                

  [tavg3_3d_cld_Cp](#Xcld)                          Upper-air cloud related diagnostics      0.512 (x.xxx)

  [tavg3_3d_mst_Cp](#Xmst)                          Upper-air diagnostics from moist         0.900 (x.xxx)
                                                    processes                                

  [tavg3_3d_trb_Cp](#Xtrb3)                         Upper-air diagnostics from turbulence    0.501 (x.xxx)

  [tavg3_3d_rad_Cp](#Xrad)                          Upper-air diagnostics from radiation     0.228 (x.xxx)

  [tavg3_3d_tdt_Cp](#tavg3_3d_tdt_cp)               Upper-air temperature tendencies by      0.445 (x.xxx)
                                                    process                                  

  [tavg3_3d_udt_Cp](#Xudt)                          Upper-air wind tendencies by process     0.557 (x.xxx)

  [tavg3_3d_qdt_Cp](#Xqdt)                          Upper-air humidity tendencies by process 0.613 (x.xxx)

  [tavg3_3d_odt_Cp](#Xodt)                          Upper-air ozone tendencies by process    0.279 (x.xxx)

  [tavg1_2d_slv_Nx](#Xslv)                          Single-level atmospheric state variables 0.546 (0.248) // 6.0
                                                                                             (2.73)

  [tavg1_2d_flx_Nx](#tavg1_2d_flx_nx)               Surface turbulent fluxes and related     0.505 (x.xxx)
                                                    quantities                               

  [tavg1_2d_rad_Nx](#Xrad2)                         Surface and TOA radiative fluxes         0.561 (x.xxx)

  [tavg1_2d_lnd_Nx](#section-15)                    Land related surface quantities          x.xxx (x.xxx)

  [tavg1_2d_int_Nx](#tavg1_2d_int_nx)               Vertical integrals                       x.xxx (x.xxx)

  **TOTAL**                                                                                  x.xxx (x.xxx)
  -----------------------------------------------------------------------------------------------------------------

# 

Table 6-2 List of chemistry collections

  ----------------------------------------------------------------------------------------------
  **Name**                              **Description**                             **Size
                                                                                    (Gbytes)**
  ------------------------------------- ------------------------------------------- ------------
  [const_2d_chm_Fx](#const_2d_chm_fx)   2-D invariants on chemistry grid            x.xxx
                                                                                    (x.xxx)

  [tavg3_3d_chm_Fv](#tavg3_3d_chm_fv)   Chemistry related 3-D at model layer        x.xxx
                                        centers                                     (x.xxx)

  [tavg3_3d_chm_Fe](#XchmFE)            Chemistry related 3-D at model layer edges  x.xxx
                                                                                    (x.xxx)

  [tavg3_2d_chm_Fx](#tavg3_2d_chm_fx)   Chemistry related 2-DSingle-level           x.xxx
                                                                                    (x.xxx)

  [tavg3_3d_chm_Nv](#tavg3_3d_chm_nv)   Accumulated transport fields at layers      x.xxx
                                                                                    (x.xxx)

  [tavg3_3d_chm_Ne](#tavg3_3d_chm_ne)   Accumulated transport fields at edges       x.xxx
                                                                                    (x.xxx)

  [inst3_3d_chm_Ne](#inst3_3d_chm_ne)   Instantaneous fields for off-line transport x.xxx
                                                                                    (x.xxx)

  **TOTAL CHEM**                                                                    x.xxx
                                                                                    (x.xxx)
  ----------------------------------------------------------------------------------------------

# 7. Metadata 

GEOS-5 gridded output files will include or be linked to two types of
metadata. When using the HDF-EOS library and tools, the EOSDIS metadata
will be used. Other utilities such as
[GrADS](http://www.iges.org/grads/) will use the CF metadata.

## 7.1 EOSDIS Metadata 

The EOSDIS toolkit will only use the EOSDIS metadata. EOSDIS identifies
two major types of metadata:, collection and granule.

Collection metadata are stored in a separate index file. This file
describes an ESDT and is like a card in a library catalog. Each GMAO
data product will have an ESDT description in the EOS Core System that
contains its unique collection attributes. [Appendix
C](#_Appendix_C:_Collection_Metadata) describes the ESDT collection
metadata.

Granule metadata is the \"table of contents\" information stored on the
data file itself. The EOSDIS granule metadata include:

-   File name (local granule ID)

-   Grid structure

-   Number of time stamps stored in the file

-   Number of vertical levels for each variable in this file

-   Names of variables in this file

-   Variable format (32-bit floating point, 16-bit integer, etc.)

-   Variable storage dimensions

time, latitude and longitude for 2-d fields

time, latitude, longitude and vertical levels 3-d fields

-   \"Missing\" value for each variable

## 7.2 CF Metadata 

When [GrADS](http://www.iges.org/grads/) or
[FERRET](http://ferret.wrc.noaa.gov/Ferret/) are used to view GEOS-5
gridded data sets, the application will use the CF metadata imbedded in
the data products. These metadata will comply with the CF conventions
and include the following information:

-   Space-time grid information (dimension variables)

-   Variable names and descriptions

-   Variable units

-   \"Missing\" value for each variable

# 8. Sample Software 

The following example illustrates the use of the standard HDF library or
the ECS HDF-EOS library to read GEOS-5 products. The program shown below
will accept as command line arguments a file name and a field name. It
will open the file, read the requested field at the first time, compute
an average for this field, and print the result to standard output.
There are two versions of this program. The first version uses the
HDF-EOS library to read the file. The second version uses the standard
HDF library to read the file. Electronic copies of these programs can be
obtained from the Operations section of the GMAO [web
page](http://gmao.gsfc.nasa.gov/operations/).

## 8.1 HDF-EOS Example 

/\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*/

/\* This program demonstrates how to read a field from a GMAO HDF-EOS
\*/

/\* product using the HDF-EOS library. It will take a file name and \*/

/\* field name on the command line, read the first time of the given \*/

/\* field, calculate an average of that time and print the average. \*/

/\* \*/

/\* usage: avg \<file name\> \<field name\> \*/

/\* \*/

/\* Rob Lucchesi \*/

/\* <rlucchesi@GMAO.gsfc.nasa.gov> \*/

/\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*/

#include \"hdf.h\"

#include \"mfhdf.h\"

#include \<stdio.h\>

main(int argc,char \*argv\[\]) {

int32 sd_id, sds_id, status;

int32 sds_index;

int32 start\[4\], edges\[4\], stride\[4\];

char \*fname, \*vname;

float32 \*data_array;

float32 avg, sum;

int32 i;

int32 file_id, gd_id;

int32 xdim, ydim, zdim, len;

if (argc != 3) {

printf(\"Usage: avg \<filename\> \<field\> \\n\");

exit (-1);

}

fname = argv\[1\];

vname = argv\[2\];

/\* Open the file (read-only) \*/

if ( (file_id = GDopen (fname, DFACC_RDONLY))\< 0) {

printf (\"Could not open %s\\n\",fname);

exit(-1);

}

/\* Attach to the EOS grid contained within the file. \*/

/\* The GMAO uses the generic name \"EOSGRID\" for the grid in all
products. \*/

if ( (gd_id = GDattach (file_id,\"EOSGRID\"))\< 0) {

printf (\"Could not open %s\\n\",fname);

exit(-1);

}

status = GDget(file_id,xdim,ydim,zdim),

/\* Set positioning arrays to read the entire field at the first time.
\*/

start\[0\] = 0;

start\[1\] = 0;

start\[2\] = 0;

start\[3\] = 0;

stride\[0\] = 1;

stride\[1\] = 1;

stride\[2\] = 1;

stride\[3\] = 1;

edges\[0\] = 1;

edges\[1\] = zdim;

edges\[2\] = ydim;

edges\[3\] = xdim;

len = xdim\*ydim\*zdim;

data_array = (float32 \*)malloc(len);

/\* Read the data into data_array \*/

status = GDreadfield (gd_id, vname, start, stride, edges, data_array);

printf (\"Read status=%d\\n\",status);

/\* Calculate and print the average \*/

sum=0.0;

for (i=0; i\<len; i++) sum += data_array\[i\];

avg = sum/(float32)len;

printf (\"Average of %s in 3 dimensions is=%f\\n\",vname,avg);

/\* Close file. \*/

status = GDdetach (gd_id);

status = GDclose (file_id);

}

## 8.2 HDF (non EOS) Example

/\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*/

/\* This program demonstrates how to read a field from a GMAO HDF-EOS
\*/

/\* product using the HDF library (HDF-EOS not required). It will take
\*/

/\* a file name and field name on the command line, read the first time
\*/

/\* of the given field, calculate an average of that time and print the
average. \*/

/\* \*/

/\* usage: avg \<file name\> \<field name\> \*/

/\* \*/

/\* Rob Lucchesi \*/

/\* <rlucchesi@GMAO.gsfc.nasa.gov> \*/

/\* \*/

/\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*/

#include \"hdf.h\"

#include \"mfhdf.h\"

#include \<stdio.h\>

main(int argc,char \*argv\[\]) {

int32 sd_id, sds_id, status;

int32 sds_index;

int32 start\[4\], edges\[4\], stride\[4\];

char \*fname, \*vname;

float32 \*data_array;

float32 avg, sum;

int32 i, xdim, ydim , zdim, len;

if (argc != 3) {

printf(\"Usage: avg \<filename\> \<field\> \\n\");

exit (-1);

}

fname = argv\[1\];

vname = argv\[2\];

/\* Open the file (read-only) \*/

if ( (sd_id = SDstart (fname, DFACC_RDONLY))\< 0) {

printf (\"Could not open %s\\n\",fname);

exit(-1);

}

/\* Find the index and ID of the SDS for the given variable name and get
its dimensions. \*/

if ( (sds_index = SDnametoindex (sd_id, vname)) \< 0) {

printf (\"Could not find %s\\n\",vname);

exit(-1);

}

sds_id = SDselect (sd_id,sds_index);

status = GDget(file_id,xdim,ydim,zdim),

/\* Set positioning arrays to read the entire field at the first time.
\*/

start\[0\] = 0;

start\[1\] = 0;

start\[2\] = 0;

start\[3\] = 0;

stride\[0\] = 1;

stride\[1\] = 1;

stride\[2\] = 1;

stride\[3\] = 1;

edges\[0\] = 1;

edges\[1\] = zdim;

edges\[2\] = ydim;

edges\[3\] = xdim;

len = xdim\*ydim\*zdim;

data_array = (float32 \*)malloc(len);

/\* Read the data into data_array \*/

status = SDreaddata (sds_id, start, stride, edges, (VOIDP) data_array);

printf (\"read status=%d\\n\",status);

/\* Calculate and print the average \*/

sum=0.0;

for (i=0; i\<len; i++) sum += data_array\[i\];

avg = sum/(float32)len;

printf (\"Average of %s in 3 dimensions is=%f\\n\",vname,avg);

/\* Close file. \*/

status = SDendaccess (sds_id);

# status = SDend (sd_id); 

}

# Appendix A: The IAU procedure 

The implementation of the Incremental Analysis Update (IAU, Bloom et
al., 1996) used for MERRA is summarized in Figure A.1. Every six hours,
at the synoptic times, an analysis is performed using backgrounds at
that time, three hours earlier, and three hours later, which
incorporates observations during the six-hour period spanned by the
three backgrounds. The results of this analysis are the products
included in the two [analysis
collections](#_5._File_Naming_Conventions). The analysis increments
(i.e., the difference between the analysis and the corresponding
synoptic background) are then divided by a time scale (in MERRA we used
6 hours) to produce an "analysis tendency." The model is then
"backed-up", restarting it from its state three hours before the
analysis time, and run for six hours, adding in the time-invariant
"analysis tendency" in addition to its normal physics tendencies. At
that point a restart is created that will be used next time the model is
backed-up, and the first background for the next analysis cycle is
saved. We refer to this first 6-hour run as the "corrector" segment of
the IAU. The run is then continued without an analysis tendency for
another six hours, saving the other two backgrounds needed by the next
analysis\-\--one at the next synoptic time and another at the end of the
six hours. We refer to this 6-hour run as the "predictor" segment of the
IAU. The entire cycle is then repeated for subsequent synoptic times.
Note that during each of the four daily analysis cycles the model is run
for 12 hours\-\--a 6-hour "corrector" followed by a 6-hour "predictor."

[]{#IAU .anchor}

![](media/image2.png){width="5.7131944444444445in"
height="2.8881944444444443in"}

**Figure A.1**

Except for the analyses themselves, all products from MERRA are produced
by the model during the corrector run segment. The sequence of corrector
segments (follow the green line in the figure) is a continuous model
run, with the extra forcing term from the analysis tendencies. The
analysis tendencies do change abruptly every six hours, but state
variables are continuous (within the model's time step) solutions of the
equations of motion, albeit with the extra forcing term.

# Appendix B: Observational Inputs to MERRA

Table B.1 Input conventional observations.

  ------------------------------------------ ----------------------------
  Radiosondes                                u, v, T, q, P~s~

  PIBAL winds                                u, v

  Wind profiles                              u, v

  Conventional, ASDAR, and MDCARS aircraft   u, v, T
  reports                                    

  NEXRAD radar winds                         u, v

  Dropsondes                                 u, v, T, P~s~

  PAOB                                       P~s~

  GMS, METEOSAT, cloud drift IR and visible  u, v
  winds                                      

  MODIS clear sky and water vapor winds      u, v

  GOES cloud drift IR winds                  u, v

  GOES water vapor cloud top winds           u, v

  Surface land observations                  P~s~

  Surface ship and buoy observations         u, v, T, q, P~s~

  SSM/I                                      Rain rate, wind speed

  TMI                                        Rain rate

  QuikSCAT                                   Wind speed and direction
  ------------------------------------------ ----------------------------

Table B.2 Input Satellite Data

+------------------------------------------+---------------------------+
| TOVS 1b Radiances                        | AMSU-A: N15, N16, N18     |
|                                          |                           |
|                                          | AMSU-B: N15, N16, N17     |
|                                          |                           |
|                                          | MHS: N18                  |
|                                          |                           |
|                                          | HIRS2: TIROS-N, N6, N7,   |
|                                          | N8, N9, N10, N11, N12,    |
|                                          | N14                       |
|                                          |                           |
|                                          | HIRS3: N16, N17           |
|                                          |                           |
|                                          | HIRS4: N18                |
|                                          |                           |
|                                          | MSU: TIROS-N, N6, N7, N8, |
|                                          | N9, N10, N11, N12, N14    |
|                                          |                           |
|                                          | SSU: TIROS-N, N6, N7, N8, |
|                                          | N9, N10, N11, N14         |
+------------------------------------------+---------------------------+
| EOS/Aqua Level 1b Radiances              | AIRS (150 channels),      |
|                                          | AMSU-A                    |
+------------------------------------------+---------------------------+
| SSM/I radiances                          | DSMP-13, DSMP-14, DSMP-15 |
|                                          | (7 channels)              |
+------------------------------------------+---------------------------+
| GOES sounder T~B~                        | GOES-08, GOES-10, GOES-12 |
|                                          | Channels 1-18             |
+------------------------------------------+---------------------------+
| SBUV2 ozone (Version 8 retrievals)       | Nimbus 7, NOAA 9, 11, 14, |
|                                          | 16, 17                    |
+------------------------------------------+---------------------------+

Table 1.2 Conventional data availability and source.

  ------------------------ ---------------------- ------------------------
  **DATA SOURCE/TYPE**     **PERIOD**             **DATA SUPPLIER**

  Radiosondes              1970 - present         NOAA/NCEP

  PIBAL winds              1970 - present         NOAA/NCEP

  Wind profiles            1992/5/14 - present    UCAR CDAS

  Conventional, ASDAR, and 1970 - present         NOAA/NCEP
  MDCARS aircraft reports                         

  Dropsondes               1970 - present         NOAA/NCEP

  PAOB                     1978 - present         NCEP CDAS

  GMS, METEOSAT, cloud     1977 -- present        NOAA/NCEP
  drift IR and visible                            
  winds                                           

  GOES cloud drift winds   1997 -- present        NOAA/NCEP

  EOS/Terra/MODIS winds    2002/7/01 - present    NOAA/NCEP

  EOS/Aqua/MODIS winds     2003/9/01 - present    NOAA/NCEP

  Surface land             1970 - present         NOAA/NCEP
  observations                                    

  Surface ship and buoy    1977 - present         NOAA/NCEP
  observations                                    

  SSM/I rain rate          1987/7 - present       NASA/GSFC/DAAC

  SSM/I V6 wind speed      1987/7 - present       RSS

  TMI rain rate            1997/12 - present      NASA/GSFC/DAAC

  QuikSCAT surface winds   1999/7 - present       JPL

  ERS-1 surface winds      1991/8/5 -- 1996/5/21  CERSAT

  ERS-2 surface winds      1996/3/19 -- 2001/1/17 CERSAT
  ------------------------ ---------------------- ------------------------

Table B.4 Satellite data availability and source

  ------------------------ ---------------------- ------------------------
  **DATA SOURCE/TYPE**     **PERIOD**             **DATA SUPPLIER**

  TOVS/tn (TIROS N)        1978/10/30 --          NCAR
                           1980/06/01             

  TOVS/na (NOAA 6)         1979/07/02 --          NCAR
                           1983/04/17             

  TOVS/nc (NOAA 7)         1981/07/11 -           NCAR
                           1986/06/01             

  TOVS/ne (NOAA 8)         1983/04/26 -           NCAR
                           1985/01/01             

  TOVS/nf (NOAA 9)         1985/01/01 -           NOAA/NESDIS & NCAR
                           1988/11/01             

  TOVS/ng (NOAA 10)        1986/11/25 -           NOAA/NESDIS & NCAR
                           1991/09/17             

  TOVS/nh (NOAA 11)        1988/09/02 -           NOAA/NESDIS & NCAR
                           1994/12/31             

  TOVS/nd (NOAA 12)        1991/08/18 -           NOAA/NESDIS & NCAR
                           1997/07/14             

  TOVS/nj (NOAA 14)        1995/01/19 - present   NOAA/NESDIS

  TOVS/nk (NOAA 15)        1998/07/01 - present   NOAA/NESDIS

  TOVS/nl (NOAA 16)        2001/03/02 - present   NOAA/NESDIS

  TOVS/nm (NOAA 17)        2003/03/01 - present   NOAA/NESDIS

  TOVS/nn (NOAA 18)        2005/10/05 -- present  NOAA/NESDIS

  EOS/Aqua                 2002/10 - present      NOAA/NESDIS

  SSM/I V6 (F08)           1987/7 - 1991/12       RSS

  SSM/I V6 (F10)           1990/12 -- 1997/11     RSS

  SSM/I V6 (F11)           1991/12 -- 2000/5      RSS

  SSM/I V6 (F13)           1995/5 - present       RSS

  SSM/I V6 (F14)           1997/5 - present       RSS

  SSM/I V6 (F15)           1999/12 -- 2006/8      RSS

  GOES sounder T~B~        2001/01 - present      NOAA/NCEP

  SBUV2 ozone (Version 8   1978/10 - present      NASA/GSFC/Code 613.3
  retrievals)                                     
  ------------------------ ---------------------- ------------------------

#   

# Appendix C: Collection Metadata 

GEOS-5 collection metadata will contain the following. To view the ESDTs
associated with GMAO products, which include collection metadata, see
the GMAO Operations web page: <http://gmao.gsfc.nasa.gov/operations>.

*ECS Collection*

Revision Date

Suggested Usage

*Single Type Collection*

Collection State

Maintenance and Update Frequency

*Spatial*

Spatial Coverage Type

*Bounding Rectangle*

West Bounding Coordinate

North Bounding Coordinate

East Bounding Coordinate

South Bounding Coordinate

*Altitude System Definition (for 3d files only)*

Altitude Datum Name

Altitude Distance Units

Altitude Encoding Method

Altitude Resolution Class

Altitude Resolution

*Depth System Definition (land surface files only)*

Depth Datum Name

Depth Distance Units

Depth Encoding Method

Depth Resolution Class

Depth Resolution

*Geographic Coordinate System*

Latitude Resolution

Longitude Resolution

Geographic Coordinate Units

*Temporal*

Time Type

Date Type

Temporal Range Type

Precision of Seconds

Ends at Present Flag

*Range Date Time*

Range Beginning Date

Range Beginning Time

Range Ending Date

Range Ending Time

*Contact Person*

Role

Hours of Service

Contact Job Position

Contact First Name

Contact Middle Name

Contact Last Name

*Contact Person Address*

Street address

City

State/Province

Postal Code

Country

*Telephone*

Telephone Container

Telephone Number

Telephone Number Type

*Email*

Electronic Mail Address

*Contact Organization*

Role

Hours of Service

Contact Instruction

Contact Organization Name

*Contact Organization Address*

Street Address

City

State/Province

Postal Code

Country

*Organization Telephone Number*

Telephone Number

Telephone Number Type

*Organizational Email*

Electronic Mail Address

*Discipline Topic Parameters*

ECS Discipline Keyword

ECS Topic Keyword

ECS Term Keyword

ECS Variable Keyword

ECS Parameter Keyword

*Temporal Keyword Class*

Temporal Keyword

*Spatial Keyword Class*

Spatial Keyword

*Processing Level*

Processing Level Description

Processing Level ID

*Analysis Source*

Analysis Short Name

Analysis Long Name

Analysis Technique

Analysis Type

*CSDT Description*

Primary CSDT

*Additional Attributes*

Additional Attribute Data Type

Additional Attribute Description

Additional Attribute Name

*Physical Parameter Details*

Parameter Units of Measure

Parameter Range

Parameter Value Accuracy

Parameter Value Accuracy Explanation

Parameter Measurement Resolution

*Storage Medium Class* (filled in by DAAC)

# Appendix D: Vertical Structure 

Pressure-level data will be output on the following 42 pressure levels:

Products on the native vertical grid will be output on the following
levels. Pressures are nominal for a 1000 hPa surface pressure and refer
to the top edge of the layer. Note that the bottom layer has a nominal
thickness of 15 hPa.

[]{#Elevs .anchor}

  --------- ------------ --------- ------------ --------- ------------ --------- ------------ --------- ------------ --------- ------------
  **Lev**   **P(hPa)**   **Lev**   **P(hPa)**   **Lev**   **P(hPa)**   **Lev**   **P(hPa)**   **Lev**   **P(hPa)**   **Lev**   **P(hPa)**

  1         0.0100       13        0.6168       25        9.2929       37        78.5123      49        450.000      61        820.000

  2         0.0200       14        0.7951       26        11.2769      38        92.3657      50        487.500      62        835.000

  3         0.0327       15        1.0194       27        13.6434      39        108.663      51        525.000      63        850.000

  4         0.0476       16        1.3005       28        16.4571      40        127.837      52        562.500      64        865.000

  5         0.0660       17        1.6508       29        19.7916      41        150.393      53        600.000      65        880.000

  6         0.0893       18        2.0850       30        23.7304      42        176.930      54        637.500      66        895.000

  7         0.1197       19        2.6202       31        28.3678      43        208.152      55        675.000      67        910.000

  8         0.1595       20        3.2764       32        33.8100      44        244.875      56        700.000      68        925.000

  9         0.2113       21        4.0766       33        40.1754      45        288.083      57        725.000      69        940.000

  10        0.2785       22        5.0468       34        47.6439      46        337.500      58        750.000      70        955.000

  11        0.3650       23        6.2168       35        56.3879      47        375.000      59        775.000      71        970.000

  12        0.4758       24        7.6198       36        66.6034      48        412.500      60        800.000      72        985.000
  --------- ------------ --------- ------------ --------- ------------ --------- ------------ --------- ------------ --------- ------------

#  

# Appendix E: GEOS-5 data collections 

This section lists the variables in eachh the data collection. More
details on the variable definitions may be found in Appendix F. Most
variables tabled in this section are hyperlinked to their definitions in
Appendix F. In the tables, variable names refer to HDF names, which are
uppercase. Sizes refer to the daily files.

## E.1 Time-independent Variables 

These are prescribed 2-dimensional fields that do not vary during the
reanalysis. They are available as:
**MERRA000.prod.assim.const_2d_asm_Nx.00000000.hdf** at the full
resolution.

### const_2d_asm_Nx 

ECS short name: **AC0NXASM**

ECS long name: MERRA DAS 2d constants,

Characteristics: **Constant at** [native resolution](#Native)

Dimensions: longitude: **540**, latitude: **361**

## E.2 Analysis Collections 

These are the fields resulting from the GSI analyses performed at the
four synoptic times (states labeled ANALYSIS in [Figure A.1](#IAU)).
They are produced on the native horizontal grid and on both model levels
and pressure levels in the vertical. The data on model levels are the
values actually analyzed.

### inst6_3d_ana_Nv 

[]{#Xana .anchor}

ECS short name: **AI6NVANA**

ECS long name: MERRA DAS 3d analyzed state,

Characteristics: **Instantaneous, on model levels, at** [native
resolution](#Native)

Dimensions: longitude: **540**, latitude: **361**, levels: **72** (see
[Appendix D](#_Appendix_D%3A_Vertical_Structure))

Times: **00, 06, 12, 18 GMT**

  ------------------------------------------------------------------------
  Variable Name      Dims    Description                         Units
  ------------------ ------- ----------------------------------- ---------
  PS                 2D      Surface pressure                    Pa

  DELP               3D      Layer pressure thickness            Pa

  T                  3D      Air temperature                     K

  U                  3D      Eastward wind component             m s^-1^

  V                  3D      Northward wind component            m s^-1^

  QV                 3D      Specific humidity                   kg kg^-1^

  O3                 3D      Ozone mixing ratio                  kg kg^-1^
  ------------------------------------------------------------------------

### inst6_3d_ana_Np

[]{#Xanap .anchor}

ECS short name: **AI6NPANA**

ECS long name: MERRA DAS 3d analyzed state on pressure,

Characteristics: **Instantaneous, on pressure levels, at** [native
resolution](#Native)

Dimensions: longitude: **540**, latitude: **361**, pressure levels:
**42** (see [Appendix D](#_Appendix_D%3A_Vertical_Structure))

Times: **00, 06, 12, 18 GMT ; monthly and seasonal also available.**

+----------------+-----+---------------------------------+------------+
| > Variable     | > D | > Description                   | > Units    |
| > Name         | ims |                                 |            |
+================+=====+=================================+============+
| > SLP          | >   | > Sea-level pressure            | > Pa       |
|                |  2D |                                 |            |
+----------------+-----+---------------------------------+------------+
| > PS           | >   | > Surface pressure              | > Pa       |
|                |  3D |                                 |            |
+----------------+-----+---------------------------------+------------+
| > H            | >   | > Geopotential height           | > m        |
|                |  3D |                                 |            |
+----------------+-----+---------------------------------+------------+
| > T            | >   | > Air temperature               | > K        |
|                |  3D |                                 |            |
+----------------+-----+---------------------------------+------------+
| > U            | >   | > Eastward wind component       | > m s^-1^  |
|                |  3D |                                 |            |
+----------------+-----+---------------------------------+------------+
| > V            | >   | > Northward wind component      | > m s^-1^  |
|                |  3D |                                 |            |
+----------------+-----+---------------------------------+------------+
| > QV           | >   | > Specific humidity             | > kg       |
|                |  3D |                                 | > kg^-1^   |
+----------------+-----+---------------------------------+------------+
| > O3           | >   | > Ozone mixing ratio            | > kg       |
|                |  3D |                                 | > kg^-1^   |
+----------------+-----+---------------------------------+------------+

##  

## E.3 History Collections 

These histories are produced from the GCM during the "corrector" segment
of the IAU cycle. All collections in this group are at [reduced
horizontal resolution](#Coarse) and 3-D fields are on [pressure
levels](#_Appendix_D%3A_Vertical_Structure).

### inst3_3d_asm_Cp 

[]{#Xasm .anchor}

ECS short name: **AI3CPASM**

ECS long name: MERRA IAU 3d assimilated state on pressure,

Characteristics: **Instantaneous, on pressure levels, at** [reduced
resolution](#Coarse)

Dimensions: longitude: **288**, latitude: **144**, pressure levels:
**42** (see [Appendix D](#_Appendix_D%3A_Vertical_Structure))

Times : **00, 03, 06, 09, 12, 15, 18, 21 GMT**

  --------------------------------------------------------------------------
  Variable Name Dims   Description                             Units
  ------------- ------ --------------------------------------- -------------
  SLP           2D     Sea-level pressure                      Pa

  PS            2D     Surface pressure                        Pa

  PHIS          2D     Surface Geopotential                    m^2^ s^-2^

  H             3D     Geopotential height                     m

  O3            3D     Ozone mixing ratio                      kg kg^-1^

  QV            3D     Specific humidity                       kg kg^-1^

  [QL](#QL)     3D     Cloud liquid water mixing ratio         kg kg^-1^

  [QI](#QL)     3D     Cloud ice mixing ratio                  kg kg^-1^

  [RH](#rh)     3D     Relative humidity                       fraction

  T             3D     Air temperature                         K

  U             3D     Eastward wind component                 m s^-1^

  V             3D     Northward wind component                m s^-1^

  E[PV](#PV)    3D     Ertel potential vorticity               K m^2^
                                                               kg^-1^s^-1^

  OMEGA         3D     Vertical pressure velocity              Pa sec^-1^
  --------------------------------------------------------------------------

###  

### tavg3_3d_cld_Cp

[]{#Xcld .anchor}

ECS short name: **AT3CPCLD**

ECS long name: MERRA IAU 3d cloud diagnostics,

Characteristics: **Time averaged, on pressure levels, at** [reduced
resolution](#Coarse)

Dimensions: longitude: **288**, latitude: **144**, levels: **42** (see
[Appendix D](#_Appendix_D%3A_Vertical_Structure))

Times : **1:30, 4:30, 7:30, 10:30, 13:30, 16:30, 19:30, 22:30 GMT**

  ------------------------------------------------------------------------------
  Variable Name        Description                                  Units
  -------------------- -------------------------------------------- ------------
  [RH](#rh)            Relative humidity                            fraction

  [QLLS](#QLLS)        Cloud liquid water mixing ratio --           kg kg^-1^
                       large-scale                                  

  [QILS](#QLLS)        Cloud ice mixing ratio -- large-scale        kg kg^-1^

  [QLAN](#QLLS)        Cloud liquid water mixing ratio -- anvils    kg kg^-1^

  [QIAN](#QLLS)        Cloud ice mixing ratio -- anvils             kg kg^-1^

  [QCCU](#QLLS)        Cloud condensate mixing ratio -- convective  kg kg^-1^
                       updraft                                      

  [CFLS](#APPENDIXC)   3-D Cloud fraction -- large scale            fraction

  [CFAN](#APPENDIXC)   3-D Cloud fraction -- anvils                 fraction

  [CFCU](#APPENDIXC)   3-D Cloud fraction -- convective             fraction
  ------------------------------------------------------------------------------

###  

### 

### tavg3_3d_mst_Cp 

[]{#Xmst .anchor}

ECS short name: **AT3CVMST**

ECS long name: MERRA IAU 3d moist processes diagnostic,

Characteristics: **Time averaged, on pressure levels, at** [reduced
resolution](#Coarse)

Dimensions: longitude: **288**, latitude: **144**, levels: **42** (see
[Appendix D](#_Appendix_D%3A_Vertical_Structure))

Times : **1:30, 4:30, 7:30, 10:30, 13:30, 16:30, 19:30, 22:30 GMT**

  ------------------------------------------------------------------------------
  Variable Name           Description                                  Units
  ----------------------- -------------------------------------------- ---------
  [CMFMC](#CMFMC)         Upward moist convective mass flux            kg m-2
                                                                       s-1

  [DQRCU](#DQRCON)        Precipitation production rate -- convective  kg kg^-1^
                                                                       s^-1^

  [DQRLSAN](#DQRCON)      Precipitation production rate -              kg kg^-1^
                          large-scale+anvil                            s^-1^

  [PFLCU](#PFLCU)         Downward flux of liquid precipitation --     kg m^-2^
                          convective                                   s^-1^

  [PFICU](#PFLCU)         Downward flux of ice precipitation --        kg m^-2^
                          convective                                   s^-1^

  [PFLLSAN](#PFLCU)       Downward flux of liquid precip -             kg m^-2^
                          large-scale+anvil                            s^-1^

  [PFILSAN](#PFLCU)       Downward flux of ice precip -                kg m^-2^
                          large-scale+anvil                            s^-1^

  [REEVAP](#REEVAP)CN     Evaporation of precipitating convective      kg kg^-1^
                          condensate                                   s^-1^

  [REEVAP](#REEVAP)LSAN   Evaporation of precipitating LS &anvil       kg kg^-1^
                          condensate                                   s^-1^
  ------------------------------------------------------------------------------

### tavg3_3d_rad_Cp 

[]{#Xrad .anchor}

ECS short name: **AT3CPRAD**

ECS long name: MERRA IAU 3d radiation diagnostics,

Characteristics: **Time averaged, on pressure levels, at [reduced
resolution](#Coarse)**

Dimensions: longitude: **288**, latitude: **144**, levels: **42** (see
[Appendix D](#_Appendix_D%3A_Vertical_Structure))

Times : **1:30, 4:30, 7:30, 10:30, 13:30, 16:30, 19:30, 22:30 GMT**

### tavg3_3d_trb_Cp 

[]{#Xtrb3 .anchor}

ECS short name: **AT3CPTRB**

ECS long name: MERRA IAU 3d turbulence diagnostics,

Characteristics: **Time averaged, on pressure levels, at [reduced
resolution](#Coarse)**

Dimensions: longitude: **288**, latitude: **144**, levels: **42** (see
[Appendix D](#_Appendix_D%3A_Vertical_Structure))

Times : **1:30, 4:30, 7:30, 10:30, 13:30, 16:30, 19:30, 22:30 GMT**

###  

### tavg3_3d_tdt_Cp

ECS short name: **AT3CPTDT**

ECS long name: MERRA IAU 3d temperature tendencies,

Characteristics: **Time averaged, on pressure levels, at** [reduced
resolution](#Coarse)

Dimensions: longitude: **288**, latitude: **144**, levels: **42** (see
[Appendix D](#_Appendix_D%3A_Vertical_Structure))

Times : **1:30, 4:30, 7:30, 10:30, 13:30, 16:30, 19:30, 22:30 GMT**

  --------------------------------------------------------------------------------
  Variable Name           Description                                     Units
  ----------------------- ----------------------------------------------- --------
  DTDTRAD                 Temperature tendency from radiation             K s-1

  [DTDTMST](#DTDTMOIST)   Temperature tendency from moist physics         K s-1

  [DTDTTRB](#DTDTTRB)     Temperature tendency from turbulence            K s-1

  [DTDTFRI](#DTDTFRI)     Temperature tendency from frictional heating    K s-1

  [DTDTGWD](#DTDTGWD)     Temperature tendency from gravity wave drag     K s-1

  [DTDTTOT](#DTDTTOT)     Temperature tendency from physics               K s-1

  [DTDTDYN](#DTDTDYN)     Temperature tendency from dynamics              K s-1

  [DTDTANA](#DTDTANA)     Temperature tendency from analysis              K s-1
  --------------------------------------------------------------------------------

### tavg3_3d_udt_Cp 

[]{#Xudt .anchor}

ECS short name: **AT3CPUDT**

ECS long name: MERRA IAU 3d eastward wind tendencies,

Characteristics: **Time averaged, on pressure levels, at** [reduced
resolution](#Coarse)

Dimensions: longitude: **288**, latitude: **144**, levels: **42** (see
[Appendix D](#_Appendix_D%3A_Vertical_Structure))

Times : **1:30, 4:30, 7:30, 10:30, 13:30, 16:30, 19:30, 22:30 GMT**

  --------------------------------------------------------------------------
  Variable Name         Description                                  Units
  --------------------- -------------------------------------------- -------
  [DUDTMST](#DUDTMST)   U-wind tendency from moist physics           m s-2

  [DUDTTRB](#DUDTTRB)   U-wind tendency from turbulence              m s-2

  [DUDTGWD](#DUDTGWD)   U-wind tend from gravity wave drag           m s-2

  [DUDTDYN](#DUDTDYN)   U-wind tendency from dynamics                m s-2

  DUDTANA               U-wind tendency from analysis                m s-2

  [DVDTMST](#DUDTMST)   V-wind tendency from moist physics           m s-2

  [DVDTTRB](#DUDTTRB)   V-wind tendency from turbulence              m s-2

  [DVDTGWD](#DUDTGWD)   V-wind tend from gravity wave drag           m s-2

  [DVDTDYN](#DUDTDYN)   V-wind tendency from dynamics                m s-2

  DVDTANA               V-wind tendency from analysis                m s-2
  --------------------------------------------------------------------------

[]{#Xqdt .anchor}

### tavg3_3d_qdt_Cp 

ECS short name: **AT3CPQDT**

ECS long name: MERRA IAU 3d moisture tendencies,

Characteristics: **Time averaged, on pressure levels, at** [reduced
resolution](#Coarse)

Dimensions: longitude: **288**, latitude: **144**, pressure levels:
**42** (see [Appendix D](#_Appendix_D%3A_Vertical_Structure))

Times : **1:30, 4:30, 7:30, 10:30, 13:30, 16:30, 19:30, 22:30 GMT**

  ------------------------------------------------------------------------------
  Variable Name           Description                                Units
  ----------------------- ------------------------------------------ -----------
  [DQVDTMST](#DQVDTMST)   Water vapor tendency from moist physics    kg kg-1 s-1

  [DQVDTTRB](#DQVDTTRB)   Water vapor tendency from turbulence       kg kg-1 s-1

  DQVDTCHM                Water vapor tendency from chemistry        kg kg-1 s-1

  DQVDTDYN                Water vapor tendency from dynamics         kg kg-1 s-1

  DQVDTANA                Water vapor tendency from analysis         kg kg-1 s-1

  [DQIDTMST](#DQVDTMST)   Ice tendency from moist physics            kg kg-1 s-1

  DQIDTTRB                Ice tendency from turbulence               kg kg-1 s-1

  DQIDTDYN                Ice tendency from dynamics                 kg kg-1 s-1

  [DQLDTMST](#DQVDTMST)   Liquid water tendency from moist physics   kg kg-1 s-1

  DQLDTTRB                Liquid tendency from turbulence            kg kg-1 s-1

  DQLDTDYN                Liquid tendency from dynamics              kg kg-1 s-1
  ------------------------------------------------------------------------------

### tavg3_3d_odt_Cp 

[]{#Xodt .anchor}

ECS short name: **AT3CPODT**

ECS long name: MERRA IAU 3d ozone tendencies,

Characteristics: **Time averaged, on pressure levels, at** [reduced
resolution](#Coarse)

Dimensions: longitude: **288**, latitude: **144**, levels: **42** (see
[Appendix D](#_Appendix_D%3A_Vertical_Structure))

Times : **1:30, 4:30, 7:30, 10:30, 13:30, 16:30, 19:30, 22:30 GMT**

  -----------------------------------------------------------------------
  Variable Name          Description                         Units
  ---------------------- ----------------------------------- ------------
  DOXDTMST               Ozone tendency from moist physics   kg kg-1 s-1

  DOXDTTRB               Ozone tendency from turbulence      kg kg-1 s-1

  DOXDTCHM               Ozone tendency from chemistry       kg kg-1 s-1

  DOXDTDYN               Ozone tendency from dynamics        kg kg-1 s-1

  DOXDTANA               Ozone tendency from analysis        kg kg-1 s-1
  -----------------------------------------------------------------------

###  

### tavg1_2d_slv_Nx 

[]{#Xslv .anchor}

ECS short name: **AT1NXSLV**

ECS long name: MERRA IAU 2d atmospheric single-level diagnostics

Characteristics: **Time averaged, single-level, at** [native
resolution](#Native)

Dimensions: longitude: **540**, latitude: **361**

Times : **0:30, 1:30, 2:30, 3:30, 4:30, ... GMT**

+-------------+----------------------------------------------+--------+
| Variable    | Description                                  | Units  |
| Name        |                                              |        |
+=============+==============================================+========+
| >           | > Sea level pressure                         | > Pa   |
| [SLP](#SLP) |                                              |        |
+-------------+----------------------------------------------+--------+
| > [PS](#PS) | > Time averaged surface pressure             | > Pa   |
+-------------+----------------------------------------------+--------+
| > **U850**  | > Eastward wind at 850 hPa                   | > m    |
|             |                                              | > s-1  |
+-------------+----------------------------------------------+--------+
| > **U500**  | > Eastward wind at 500 hPa                   | > m    |
|             |                                              | > s-1  |
+-------------+----------------------------------------------+--------+
| > **U250**  | > Eastward wind at 250 hPa                   | > m    |
|             |                                              | > s-1  |
+-------------+----------------------------------------------+--------+
| > **V850**  | > Northward wind at 850 hPa                  | > m    |
|             |                                              | > s-1  |
+-------------+----------------------------------------------+--------+
| > **V500**  | > Northward wind at 500 hPa                  | > m    |
|             |                                              | > s-1  |
+-------------+----------------------------------------------+--------+
| > **V250**  | > Northward wind at 250 hPa                  | > m    |
|             |                                              | > s-1  |
+-------------+----------------------------------------------+--------+
| > **T850**  | > Temperature at 850 hPa                     | > K    |
+-------------+----------------------------------------------+--------+
| > **T500**  | > Temperature at 500 hPa                     | > K    |
+-------------+----------------------------------------------+--------+
| > **T250**  | > Temperature at 250 hPa                     | > K    |
+-------------+----------------------------------------------+--------+
| > **Q850**  | > Specific humidity at 850 hPa               | > kg   |
|             |                                              | > kg-1 |
+-------------+----------------------------------------------+--------+
| > **Q500**  | > Specific humidity at 500 hPa               | > kg   |
|             |                                              | > kg-1 |
+-------------+----------------------------------------------+--------+
| > **Q250**  | > Specific humidity at 250 hPa               | > kg   |
|             |                                              | > kg-1 |
+-------------+----------------------------------------------+--------+
| > **H850**  | > Height at 850 hPa                          | > m    |
+-------------+----------------------------------------------+--------+
| > **H500**  | > Height at 500 hPa                          | > m    |
+-------------+----------------------------------------------+--------+
| > **H250**  | > Height at 250 hPa                          | > m    |
+-------------+----------------------------------------------+--------+
| > *         | > Vertical pressure velocity at 500 hPa      | > Pa   |
| *OMEGA500** |                                              | > s-1  |
+-------------+----------------------------------------------+--------+
| > [U        | > Eastward wind at 10 m above displacement   | > m    |
| 10M](#U50M) | > height                                     | > s-1  |
+-------------+----------------------------------------------+--------+
| > [         | > Eastward wind at 2 m above the             | > m    |
| U2M](#U50M) | > displacement height                        | > s-1  |
+-------------+----------------------------------------------+--------+
| > [U        | > Eastward wind at 50 m above surface        | > m    |
| 50M](#U50M) |                                              | > s-1  |
+-------------+----------------------------------------------+--------+
| > [V        | > Northward wind at 10 m above the           | > m    |
| 10M](#V50M) | > displacement height                        | > s-1  |
+-------------+----------------------------------------------+--------+
| > [         | > Northward wind at 2 m above the            | > m    |
| V2M](#V50M) | > displacement height                        | > s-1  |
+-------------+----------------------------------------------+--------+
| > [V        | > Northward wind at 50 m above surface       | > m    |
| 50M](#V50M) |                                              | > s-1  |
+-------------+----------------------------------------------+--------+
| > [T        | > Temperature at 10 m above the displacement | > K    |
| 10M](#T10M) | > height                                     |        |
+-------------+----------------------------------------------+--------+
| > [         | > Temperature at 2 m above the displacement  | > K    |
| T2M](#T10M) | > height                                     |        |
+-------------+----------------------------------------------+--------+
| > [QV1      | > Specific humidity at 10 m above the        | > kg   |
| 0M](#QV10M) | > displacement height                        | > kg-1 |
+-------------+----------------------------------------------+--------+
| > [QV       | > Specific humidity at 2 m above the         | > kg   |
| 2M](#QV10M) | > displacement height                        | > kg-1 |
+-------------+----------------------------------------------+--------+
| > TS        | > Surface skin temperature                   | > K    |
+-------------+----------------------------------------------+--------+
| > [DIS      | > Displacement height                        | > m    |
| PH](#DISPH) |                                              |        |
+-------------+----------------------------------------------+--------+
| > [TROP     | > PV based tropopause pressure               | > Pa   |
| P](#TROPP)V |                                              |        |
+-------------+----------------------------------------------+--------+
| > [TROP     | > T based tropopause pressure                | > Pa   |
| P](#TROPP)T |                                              |        |
+-------------+----------------------------------------------+--------+
| > [TROP     | > Blended tropopause pressure                | > Pa   |
| P](#TROPP)B |                                              |        |
+-------------+----------------------------------------------+--------+
| > [TRO      | > Tropopause temperature                     | > K    |
| PT](#TROPT) |                                              |        |
+-------------+----------------------------------------------+--------+
| > [TRO      | > Tropopause specific humidity               | > kg   |
| PQ](#TROPQ) |                                              | > kg-1 |
+-------------+----------------------------------------------+--------+
| [CLDPR      | Cloud-top pressure                           | Pa     |
| S](#CLDPRS) |                                              |        |
+-------------+----------------------------------------------+--------+
| [CLDTM      | Cloud-top temperature                        | K      |
| P](#CLDPRS) |                                              |        |
+-------------+----------------------------------------------+--------+

###  

### tavg1_2d_flx_Nx 

ECS short name: **AT1NXFLX**

ECS long name: MERRA IAU 2d surface turbulent flux diagnostics

Characteristics: **Time averaged, single level, at** [native
resolution](#Native)

Dimensions: longitude: **540**, latitude: **361**

Times : **0:30, 1:30, 2:30, 3:30, 4:30, ... GMT**

+--------------+---------------------------------------+--------------+
| > Variable   | > Description                         | > Units      |
| > Name       |                                       |              |
+==============+=======================================+==============+
| > [EF        | > Latent heat flux (positive upward)  | > W m-2      |
| LUX](#EFLUX) |                                       |              |
+--------------+---------------------------------------+--------------+
| > [          | > Surface evaporation                 | > kg m-2 s-1 |
| EVAP](#EVAP) |                                       |              |
+--------------+---------------------------------------+--------------+
| > [HF        | > Sensible heat flux (positive        | > W m-2      |
| LUX](#HFLUX) | > upward)                             |              |
+--------------+---------------------------------------+--------------+
| > [          | > Eastward surface wind stress        | > N m-2      |
| TAUX](#TAUX) |                                       |              |
+--------------+---------------------------------------+--------------+
| > [          | > Northward surface wind stress       | > N m-2      |
| TAUY](#TAUX) |                                       |              |
+--------------+---------------------------------------+--------------+
| > [TAUG      | > Eastward gravity wave surface       | > N m-2      |
| WX](#TAUGWX) | > stress                              |              |
+--------------+---------------------------------------+--------------+
| > [TAUG      | > Northward gravity wave surface      | > N m-2      |
| WY](#TAUGWX) | > stress                              |              |
+--------------+---------------------------------------+--------------+
| > [          | > Planetary boundary layer height     | > m          |
| PBLH](#PBLH) |                                       |              |
+--------------+---------------------------------------+--------------+
| > [DI        | > Displacement height                 | > m          |
| SPH](#DISPH) |                                       |              |
+--------------+---------------------------------------+--------------+
| > [BS        | > Surface buoyancy scale              | > m s-1      |
| TAR](#BSTAR) |                                       |              |
+--------------+---------------------------------------+--------------+
| > [US        | > Surface velocity scale              | > m s-1      |
| TAR](#USTAR) |                                       |              |
+--------------+---------------------------------------+--------------+
| > TSTAR      | > Surface temperature scale           | > K          |
+--------------+---------------------------------------+--------------+
| > QSTAR      | > Surface humidity scale              | > kg kg-1    |
+--------------+---------------------------------------+--------------+
| > RI         | > Surface Richardson number           | > no         |
|              |                                       | ndimensional |
+--------------+---------------------------------------+--------------+
| >            | > Roughness length, sensible heat     | > m          |
|  [Z0H](#Z0H) |                                       |              |
+--------------+---------------------------------------+--------------+
| >            | > Roughness length, momentum          | > m          |
|  [Z0M](#Z0M) |                                       |              |
+--------------+---------------------------------------+--------------+
| > HLML       | > Height of center of lowest model    | > m          |
|              | > layer                               |              |
+--------------+---------------------------------------+--------------+
| > TLML       | > Temperature of lowest model layer   | > K          |
+--------------+---------------------------------------+--------------+
| > QLML       | > Specific humidity of lowest model   | > kg kg-1    |
|              | > layer                               |              |
+--------------+---------------------------------------+--------------+
| > ULML       | > Eastward wind of lowest model layer | > m s-1      |
+--------------+---------------------------------------+--------------+
| > VLML       | > Northward wind of lowest model      | > m s-1      |
|              | > layer                               |              |
+--------------+---------------------------------------+--------------+
| > RHOA       | > Surface air density                 | > kg m-3     |
+--------------+---------------------------------------+--------------+
| > SPEED      | > Effective surface wind speed        | > m s-1      |
+--------------+---------------------------------------+--------------+
| > CDH        | > Surface exchange coefficient for    | > kg m-2 s-1 |
|              | > heat                                |              |
+--------------+---------------------------------------+--------------+
| > CDQ        | > Surface exchange coefficient for    | > kg m-2 s-1 |
|              | > moisture                            |              |
+--------------+---------------------------------------+--------------+
| > CDM        | > Surface exchange coefficient for    | > kg m-2 s-1 |
|              | > momentum                            |              |
+--------------+---------------------------------------+--------------+
| > CN         | > Surface neutral drag coefficient    | > no         |
|              |                                       | ndimensional |
+--------------+---------------------------------------+--------------+
| > TSH        | > Effective turbulence skin           | > K          |
|              | > temperature                         |              |
+--------------+---------------------------------------+--------------+
| > QSH        | > Effective turbulence skin humidity  | > kg kg-1    |
+--------------+---------------------------------------+--------------+
| [PRECAN      | Surface precipitation flux from       | kg m^-2^     |
| V](#PRECANV) | anvils                                | s^-1^        |
+--------------+---------------------------------------+--------------+
| [PRECCO      | Surface precipitation flux from       | kg m^-2^     |
| N](#PRECANV) | convection                            | s^-1^        |
+--------------+---------------------------------------+--------------+
| [PRECLS      | Surface precipitation flux from       | kg m-2 s-1   |
| C](#PRECANV) | large-scale                           |              |
+--------------+---------------------------------------+--------------+
| [PRECSN      | Surface snowfall flux                 | kg m^-2^     |
| O](#PRECSNO) |                                       | s^-1^        |
+--------------+---------------------------------------+--------------+
| [PRECTO      | Total surface precipitation flux      | kg m^-2^     |
| T](#PRECTOT) |                                       | s^-1^        |
+--------------+---------------------------------------+--------------+
| PGENTOT      | Total generation of precipitation     | kg m^-2^     |
|              |                                       | s^-1^        |
+--------------+---------------------------------------+--------------+

###  

### tavg1_2d_rad_Nx 

[]{#Xrad2 .anchor}

ECS short name: **AT1NXRAD**

ECS long name: MERRA IAU 2d surface and TOA radiation fluxes

Characteristics: **Time averaged, single level, at** [native
resolution](#Native)

Dimensions : longitude : **540**, latitude : **361**

Times : **0 :30, 1 :30, 2 :30, 3 :30, 4 :30, ... GMT**

  -------------------------------------------------------------------------------------
  Variable Name           Description                                   Units
  ----------------------- --------------------------------------------- ---------------
  [EMIS](#EMIS)           Surface emissivity                            fraction

  TS                      Surface skin temperature                      K

  [ALBEDO](#ALBEDO)       Surface albedo                                fraction

  [ALBNIRDF](#ALBVSIDF)   Diffuse beam NIR surface albedo               fraction

  [ALBNIRDR](#ALBVSIDF)   Direct beam NIR surface albedo                fraction

  [ALBVISDF](#ALBVSIDF)   Diffuse beam VIS-UV surface albedo            fraction

  [ALBVISDR](#ALBVSIDF)   Direct beam VIS-UV surface albedo             fraction

  LWGEM                   Emitted longwave at the surface               W m-2

  LWGAB                   Absorbed longwave at the surface              W m-2

  LWGABCLR                Absorbed longwave at the surface with no      W m-2
                          clouds                                        

  LWGABCLRCLN             Absorbed longwave at the surface with no      W m-2
                          clouds or aerosol                             

  LWGNT                   Net downward longwave flux at the surface     W m-2

  LWGNTCLR                Net downward longwave flux at the surface for W m-2
                          cloud-free sky                                

  LWGNTCLRCLN             Net downward longwave flux at the surface for W m-2
                          clear sky                                     

  [LWTUP](#LWTUP)         Upward longwave flux at top of atmosphere     W m-2
                          (TOA)                                         

  [LWTUPCLR](#LWTUP)      Upward longwave flux at TOA assuming clear    W m-2
                          sky                                           

  LWTUPCLRCLN             Upward longwave flux at TOA assuming clear    W m-2
                          clean sky                                     

  [SWTDN](#SWGDN)         TOA incident shortwave flux                   W m-2

  [SWGDN](#SWGDN)         Surface incident shortwave flux               W m-2

  [SWGDNCLR](#SWGDN)      Surface incident shortwave flux assuming      W m-2
                          clear sky                                     

  [SWGNT](#SWGNT)         Surface net downward shortwave flux           W m-2

  [SWGNTCLR](#SWGNT)      Surface net downward shortwave flux assuming  W m-2
                          clear sky                                     

  [SWGNTCLN](#SWGNT)      Surface net downward shortwave flux assuming  W m-2
                          clean sky                                     

  [SWGNTCLRCLN](#SWGNT)   Surface net downward shortwave flux assuming  W m-2
                          clear clean sky                               

  [SWTNT](#SWGNT)         TOA outgoing shortwave flux                   W m-2

  [SWTNTCLR](#SWGNT)      TOA outgoing shortwave flux assuming clear    W m-2
                          sky                                           

  [SWTNTCLN](#SWGNT)      TOA outgoing shortwave flux assuming clean    W m-2
                          sky                                           

  [SWTNTCLRCLN](#SWGNT)   TOA outgoing shortwave flux assuming clear    W m-2
                          clean sky                                     

  [TAUHGH](#TAUHGH)       Optical thickness of high clouds              dimensionless

  [TAULOW](#TAUHGH)       Optical thickness of low clouds               dimensionless

  [TAUMID](#TAUHGH)       Optical thickness of mid-level clouds         dimensionless

  [TAUTOT](#TAUHGH)       Optical thickness of all clouds               dimensionless

  [CLDHGH](#CLDHIGH)      High-level (above 400 hPa) cloud fraction     fraction

  [CLDLOW](#CLDHIGH)      Low-level (1000-700 hPa) cloud fraction       fraction

  [CLDMID](#CLDHIGH)      Mid-level (700-400 hPa) cloud fraction        fraction

  [CLDTOT](#CLDHIGH)      Total cloud fraction                          fraction
  -------------------------------------------------------------------------------------

###  

### tavg1_2d_lnd_Nx 

ECS short name: **AT1NXLND**

ECS long name: MERRA IAU 2d land surface diagnostics

Characteristics: **Time averaged, single level, at** [native
resolution](#Native)

Dimensions: longitude: **540**, latitude: **361**

Times : **0:30, 1:30, 2:30, 3:30, 4:30, ... GMT**

  --------------------------------------------------------------------------
  Variable Name           Description                            Units
  ----------------------- -------------------------------------- -----------
  [GRN](#GRN)             Vegetation greenness fraction          Fraction

  [LAI](#LAI)             Leaf area index                        m2 m-2

  [GWETROOT](#GWETROOT)   Root zone soil wetness                 fraction

  [GWETTOP](#GWETROOT)    Top soil layer wetness                 fraction

  TPSNOW                  Top snow layer temperature             K

  TUNST                   Surface temperature of unsaturated     K
                          zone                                   

  TSAT                    Surface temperature of saturated zone  K

  TWLT                    Surface temperature of wilted zone     K

  [PRECSNO](#PRECSNO)     Surface snowfall                       kg m-2 s-1

  [PRECTOT](#PRECTOT)     Total surface precipitation            kg m-2 s-1

  SNOMAS                  Snow mass                              kg m-2

  SNODP                   Snow depth                             m

  EVPSOIL                 Bare soil eEvaporation                 W m-2

  EVPTRNS                 Transpiration                          W m-2

  EVPINTR                 Interception loss                      W m-2

  EVPSBLN                 Sublimation                            W m-2

  RUNOFF                  Overland runoff                        kg m-2 s-1

  BASEFLOW                Baseflow                               kg m-2 s-1

  SMLAND                  Snowmelt                               kg m-2 s-1

  FRUNST                  Fractional unsaturated area            fraction

  FRSAT                   Fractional saturated area              fraction

  FRSNO                   Fractional snow-covered area           fraction

  FRWLT                   Fractional wilting area                fraction

  [PARDF](#PARDF)         Surface downward PAR diffuse flux      W m-2

  [PARDR](#PARDF)         Surface downward PAR beam flux         W m-2

  SHLAND                  Sensible heat flux from land           W m-2

  LHLAND                  Latent heat flux from land             W m-2

  EVLAND                  Evaporation from land                  kg m-2 s-1

  LWLAND                  Net downward longwave flux over land   W m-2

  SWLAND                  Net downward shortwave flux over land  W m-2

  GHLAND                  Downward heat flux at base of top soil W m-2
                          layer                                  

  TWLAND                  Total water store in land reservoirs   kg m-2

  TELAND                  Energy store in all land reservoirs    J m-2

  WCHANGE                 Total land water change per unit time  kg m-2 s-1

  ECHANGE                 Total land energy change per unit time W m-2

  SPLAND                  Spurious land energy source            W m-2
  --------------------------------------------------------------------------

### tavg1_2d_int_Nx 

ECS short name: **AT1NXINT**

ECS long name: MERRA IAU 2d Vertical integrals

Characteristics: **Time averaged, single level, at** [native
resolution](#Native)

Dimensions : longitude : **540**, latitude : **361**

Times : **0 :30, 1 :30, 2 :30, 3 :30, 4 :30, ... GMT**

  --------------------------------------------------------------------------
  Variable Name   Description                                    Units
  --------------- ---------------------------------------------- -----------
  [TO3](#TO3)     Total column ozone                             Dobson

  [TTO3](#TTO3)   Tropospheric total column ozone                Dobson

  DMDTANA         Vertically integrated atmospheric mass         kg m-2 s-1
                  tendency for analysis                          

  DMDTDYN         Vertically integrated atmospheric mass         kg m-2 s-1
                  tendency for dynamics                          

  DQVDTDYN        Vertically integrated water tendency for       kg m-2 s-1
                  dynamics                                       

  DQVDTMST        Vertically integrated water tendency for moist kg m-2 s-1

  DQVDTTRB        Vertically integrated water tendency for       kg m-2 s-1
                  turbulence                                     

  DQVDTCHM        Vertically integrated water tendency for       kg m-2 s-1
                  chemistry                                      

  DQVDTANA        Vertically integrated water tendency for       kg m-2 s-1
                  analysis                                       

  DQLDTDYN        Vertically integrated liquid water tendency    kg m-2 s-1
                  for dynamics                                   

  DQLDTMST        Vertically integrated liquid water tendency    kg m-2 s-1
                  for moist                                      

  DQIDTDYN        Vertically integrated ice water tendency for   kg m-2 s-1
                  dynamics                                       

  DQIDTMST        Vertically integrated ice water tendency for   kg m-2 s-1
                  moist                                          

  DOXDTDYN        Vertically integrated total ozone tendency for kg m-2 s-1
                  dynamics                                       

  DOXDTCHM        Vertically integrated total ozone tendency for kg m-2 s-1
                  dynamics                                       

  DOXDTANA        Vertically integrated total ozone tendency for kg m-2 s-1
                  analysis                                       

  DKEDTDYN        Vertically integrated kinetic energy tendency  W m-2
                  for dynamics                                   

  DPEDTDYN        Vertically integrated cpT tendency for         W m-2
                  dynamics                                       

  DTEDTDYN        Ps phis tendency for dynamics                  W m-2

  DKEDTPHY        Vertically integrated kinetic energy tendency  W m-2
                  for physics                                    

  DPEDTPHY        Vertically integrated cpT tendency for physics W m-2

  DTEDTPHY        Ps phis tendency for physics                   W m-2

  DKEDTANA        Vertically integrated kinetic energy tendency  W m-2
                  for analysis                                   

  DPEDTANA        Vertically integrated cpT tendency for         W m-2
                  analysis                                       

  DTEDTANA        Ps phis tendency for analysis                  W m-2

  UFLXCPT         Vertically integrated eastward flux of dry     J m-1 s-1
                  enthalpy                                       

  VFLXCPT         Vertically integrated northward flux of dry    J m-1 s-1
                  enthalpy                                       

  UFLXPHI         Vertically integrated eastward flux of         J m-1 s-1
                  geopotential                                   

  VFLXPHI         Vertically integrated northward flux of        J m-1 s-1
                  geopotential                                   

  UFLXKE          Vertically integrated eastward flux of kinetic J m-1 s-1
                  energy                                         

  VFLXKE          Vertically integrated northward flux of        J m-1 s-1
                  kinetic energy                                 

  UFLXQV          Vertically integrated eastward flux of         kg m-1 s-1
                  specific humidity                              

  VFLXQV          Vertically integrated northward flux of        kg m-1 s-1
                  specific humidity                              

  UFLXQL          Vertically integrated eastward flux of liquid  kg m-1 s-1
                  condensate                                     

  VFLXQL          Vertically integrated northward flux of liquid kg m-1 s-1
                  condensate                                     

  UFLXQI          Vertically integrated eastward flux of ice     kg m-1 s-1
                  condensate                                     

  VFLXQI          Vertically integrated northward flux of ice    kg m-1 s-1
                  condensate                                     

  CONVCPT         Vertically integrated convergence of dry       W m-2
                  enthalpy                                       

  CONVPHI         Vertically integrated convergence of           W m-2
                  geopotential                                   

  CONVKE          Vertically integrated convergence of kinetic   W m-2
                  energy                                         

  KEGEN           Vertically integrated generation of kinetic    W m-2
                  energy                                         

  KEGWD                                                          

  KERAY                                                          

  KEBKG                                                          

  KEORO                                                          

  KETRB                                                          

  KESRF                                                          

  KEINT                                                          

  KETOP                                                          

  KEMST                                                          
  --------------------------------------------------------------------------

##  

### inst1_2d_int_Nx 

ECS short name: **AI1NXINT**

ECS long name: MERRA IAU 2d Vertical integrals

Characteristics: **Instantaneous, single level, at** [native
resolution](#Native)

Dimensions: longitude: **540**, latitude: **361**

Times : **0, 1, 2, 3, 4, ...,23 GMT**

  ------------------------------------------------------------------------
  Variable Name Description                                    Units
  ------------- ---------------------------------------------- -----------
  TQV           Total water vapor                              kg m-2

  [TQI](#TQL)   Total cloud ice water                          kg m-2

  [TQL](#TQL)   Total cloud liquid water                       kg m-2

  TOX           Total column odd oxygen                        kg m-2

  MASS          Atmospheric mass                               kg m-2

  KE            Kinetic Energy                                 J m-2

  CPT           Dry enthalpy                                   J m-2
  ------------------------------------------------------------------------

##  

## E.4 Chemistry Forcing Files 

These histories are intended for forcing off-line chemistry/aerosol
models with the results of the reanalysis. Like other histories, they
are produced from the GCM during the "corrector" segment of the IAU
cycle. As explained in [Appendix A](#_Appendix_A:_The_IAU_procedure),
such results represent a continuous evolution of the model's state,
without the shocks of data insertion and initialization. By doing it in
this way, we can provide consistent data at intervals finer than the
six-hour analysis interval. In order to provide the most accurate
forcing for off-line calculations, these forcings are produced at
3-hourly intervals and on the native vertical grid using a reduced
horizontal resolution version of the model's horizontal grid. This
horizontal grid was chosen for backward compatibility with earlier
products. In addition, the last three streams in this section consist of
those fields needed to reproduce as closely as possible the model's
large-scale transport calculation. These are on the 3-dimansional C-grid
used by the model and can reproduce, within time truncation, the
[model's continuity equation](#MFZ). These native streams are fairly
specialized and are intended primarily for users of Goddard's Chemistry
Transport Model or its Finite-Volume advection module.

### const_2d_chm_Fx 

ECS short name: **AC0FXCNS**

ECS long name: MERRA CHM 2d constants,

Characteristics: **Constant at** [reduced FV resolution](#FVCoarse)

Dimensions: longitude: **288**, latitude: **181**

+------------+----------------------------------------------+----------+
| Variable   | Description                                  | Units    |
| Name       |                                              |          |
+============+==============================================+==========+
| [PH        | > Surface geopotential                       | m^2^     |
| IS](#PHIS) |                                              | s^-2^    |
+------------+----------------------------------------------+----------+
| [          | > Standard deviation of topography for       | m        |
| SGH](#SGH) | > gravity wave drag                          |          |
+------------+----------------------------------------------+----------+
| [FRLAKE    | > Fraction of lake type in grid box          | fraction |
| ](#FRLAKE) |                                              |          |
+------------+----------------------------------------------+----------+
| [FRLAND    | > Fraction of land type in grid box          | fraction |
| ](#FRLAKE) |                                              |          |
+------------+----------------------------------------------+----------+
| [FRLANDICE | > Fraction of land ice type in grid box      | fraction |
| ](#FRLAKE) |                                              |          |
+------------+----------------------------------------------+----------+
| [FROCEAN   | > Fraction of ocean in grid box              | fraction |
| ](#FRLAKE) |                                              |          |
+------------+----------------------------------------------+----------+

### tavg3_3d_chm_Fv

ECS short name: **AT3FVCHM**

ECS long name: MERRA IAU 3d Chem On Layers

Characteristics: **Time averaged, 3D model levels, at** [reduced FV
resolution](#FVCoarse)

Dimensions: longitude: **288**, latitude: **181**, levels: **72** (see
[Appendix D](#_Appendix_D%3A_Vertical_Structure))

Times : **1:30, 4:30, 7:30, 10:30, 13:30, 16:30, 19:30, 22:30 GMT**

  -----------------------------------------------------------------------------------
  Variable Name        Description                                   Units
  -------------------- --------------------------------------------- ----------------
  [DELP](#DELP)        Layer pressure thickness                      Pa

  T                    Air temperature                               K

  QV                   Specific humidity                             kg kg-1

  [QL](#QL)            Cloud liquid water mixing ratio               kg kg-1

  [QI](#QL)            Cloud ice mixing ratio                        kg kg-1

  U                    Eastward component of wind                    m s-1

  V                    Northward component of wind                   M s-1

  [CFLS](#APPENDIXC)   Large-scale cloud fraction                    fraction

  [CFAN](#APPENDIXC)   Anvil cloud fraction                          fraction

  [CFCU](#APPENDIXC)   Convective cloud fraction                     fraction

  [DQRCON](#DQRCON)    Precipitation production rate -- convective   kg kg^-1^ s^-1^

  [DQRLSC](#DQRCON)    Precipitation production rate - large-scale   kg kg^-1^ s^-1^

  [DQRANV](#dqrccon)   Precipitation production rate - anvils        kg kg^-1^ s^-1^

  [DTRAIN](#DTRAIN)    Detrainment cloud mass flux                   kg m-2 s-1

  [TAUCLI](#TAUCLI)    Layer ice cloud optical thickness             nondimensional

  [TAUCLW](#TAUCLI)    Layer liquid cloud optical thickness          nondimensional
  -----------------------------------------------------------------------------------

[]{#XchmFE .anchor}

### tavg3_3d_chm_Fe

ECS short name: **AT3FECHM**

ECS long name: MERRA IAU 3d Chem On Layer Edges

Characteristics: **Time averaged, 3D model levels, at** [reduced FV
resolution](#FVCoarse)

Dimensions: longitude: **288**, latitude: **181**, levels: **73** (see
[Appendix D](#_Appendix_D%3A_Vertical_Structure))

Times : **1:30, 4:30, 7:30, 10:30, 13:30, 16:30, 19:30, 22:30 GMT**

  -----------------------------------------------------------------------
  Variable Name         Description                            Units
  --------------------- -------------------------------------- ----------
  [MFZ](#MFZ)           Upward resolved mass flux              kg m-2 s-1

  [CMFMC](#CMFMC)       Upward moist convective mass flux      kg m-2 s-1

  PFLLSAN               Liquid large-scale plus anvil          kg m-2 s-1
                        precipitation                          

  PFILSAN               Ice large-scale plus anvil             kg m-2 s-1
                        precipitation                          

  PFLCU                 Liquid convective precipitation        kg m-2 s-1

  PFICU                 Ice convective precipitation           kg m-2 s-1

  [KH](#KH)             Total scalar diffusivity               m2 s-1
  -----------------------------------------------------------------------

### tavg3_2d_chm_Fx

ECS short name: **AT3FXCHM**

ECS long name: MERRA IAU 2d Chem

Characteristics: **Time averaged, single-level, at** [reduced FV
resolution](#FVCoarse)

Dimensions: longitude: **288**, latitude: **181** (see [Appendix
D](#_Appendix_D%3A_Vertical_Structure))

Times : **1:30, 4:30, 7:30, 10:30, 13:30, 16:30, 19:30, 22:30 GMT**

  -------------------------------------------------------------------------
  Variable Name           Description                            Units
  ----------------------- -------------------------------------- ----------
  [PRECANV](#PRECANV)     Surface precipitation flux from anvils kg m-2 s-1

  [PRECCON](#PRECANV)     Surface precipitation flux from        kg m-2 s-1
                          convection                             

  [PRECLSC](#PRECANV)     Surface precipitation flux from        kg m-2 s-1
                          large-scale                            

  FRCLS                   Fractional area of large-scale         Fraction
                          precipitation                          

  FRCAN                   Fractional area of anvil precipitation Fraction

  FRCCN                   Fractional area of convective          Fraction
                          precipitation                          

  [PRECSNO](#PRECSNO)     Surface snowfall flux                  kg m-2 s-1

  TS                      Surface skin temperature               K

  [QV2M](#QV10M)          Specific humidity 2 m above            kg kg-1
                          displacement height                    

  [T2M](#T10M)            Temperature 2 m above displacement     K
                          height                                 

  [U10M](#U50M)           Eastward wind 10 m above displacement  m s-1
                          height                                 

  [V10M](#V50M)           Northward wind 10 m above the          m s-1
                          displacement height                    

  [PARDF](#PARDF)         Surface downward PAR diffuse flux      W m-2

  [PARDR](#PARDF)         Surface downward PAR beam flux         W m-2

  [NIRDF](#PARDF)         Surface downward NIR diffuse flux      W m-2

  [NIRDR](#PARDF)         Surface downward NIR beam flux         W m-2

  LWGNET                  Surfece net downward longwave flux     W m-2

  SWGNET                  Net surface downward shortwave flux    W m-2

  LWGDWN                  Surface downward longwave flux         W m-2

  SWGDWN                  Surface downward shortwave flux        W m-2

  [EVAP](#EVAP)           Surface evaporation                    kg m-2 s-1

  [HFLUX](#HFLUX)         Sensible heat flux (positive upward)   W m-2

  [GWETROOT](#GWETROOT)   Root zone soil wetness                 fraction

  [GWETTOP](#GWETROOT)    Top soil layer wetness                 fraction

  [CLDHGH](#CLDHIGH)      High-level (above 400 hPa) cloud       fration
                          fraction                               

  [CLDLOW](#CLDHIGH)      Low-level (1000-700 hPa) cloud         fraction
                          fraction                               

  [CLDMID](#CLDHIGH)      Mid-level (700-400 hPa) cloud fraction fraction

  [CLDTOT](#CLDHIGH)      Total cloud fraction                   fraction

  [PBLH](#PBLH)           Planetary boundary layer height above  m
                          surface                                

  PBLTOP                  Pressure at PBL top                    Pa

  PS                      Surface pressure                       Pa
  -------------------------------------------------------------------------

### tavg3_3d_chm_Nv

ECS short name: **AT3NVCHM**

ECS long name: MERRA IAU 3d Chem On Layers

Characteristics: **Time averaged, 3D model levels, at** [native
resolution](#Coarse)

Dimensions: longitude: **540**, latitude: **361**, model levels: **72**
(see [Appendix D](#_Appendix_D%3A_Vertical_Structure))

Times : **1:30, 4:30, 7:30, 10:30, 13:30, 16:30, 19:30, 22:30 GMT**

  -----------------------------------------------------------------------------
  Variable Name       Description                                    Units
  ------------------- ---------------------------------------------- ----------
  MFXC                Eastward mass flux on C-Grid                   Pa m s-1

  MFYC                Northward mass flux on C-Grid                  Pa m s-1

  UC                  Eastward component of wind on C-Grid           m s-1

  VC                  Northward component of wind on C-Grid          m s-1

  [DTRAIN](#DTRAIN)   Detrainment cloud mass flux                    kg m-2 s-1
  -----------------------------------------------------------------------------

###  

### tavg3_3d_chm_Ne 

ECS short name: **AT3NECHM**

ECS long name: MERRA IAU 3d Chem On Layer Edges

Characteristics: **Time averaged, 3D model levels, at** [native
resolution](#Coarse)

Dimensions: longitude: **540**, latitude: **361**, model levels: **73**
(see [Appendix D](#_Appendix_D%3A_Vertical_Structure))

Times : **1:30, 4:30, 7:30, 10:30, 13:30, 16:30, 19:30, 22:30 GMT**

  ---------------------------------------------------------------------------
  Variable Name     Description                                    Units
  ----------------- ---------------------------------------------- ----------
  MFZ               Upward mass flux on C-Grid                     kg m-2 s-1

  [CMFMC](#CMFMC)   Upward moist convective mass flux              kg m-2 s-1

  [KH](#KH)         Total scalar diffusivity                       m2 s-1
  ---------------------------------------------------------------------------

### inst3_3d_chm_Ne 

ECS short name: **AT3NECHM**

ECS long name: MERRA IAU 3d Chem On Layer Edges

Characteristics: **Instantaneous, 3D model levels, at** [native
resolution](#Coarse)

Dimensions: longitude: **540**, latitude: **361**, model levels: **73**
(see [Appendix D](#_Appendix_D%3A_Vertical_Structure))

Times : **0, 3, 6, 9, 12, 15, 18, 21 -GMT**

  -----------------------------------------------------------------------
  Variable Name Description                                    Units
  ------------- ---------------------------------------------- ----------
  PLE           Edge pressures                                 Pa

  -----------------------------------------------------------------------

# Appendix F: Detailed Description of Output Variables 

## F.1 Three-dimensional Fields 

**CFLS,CFAN,CFCU:** The horizontal fractional cloud cover of each cloud
type for each layer. In the vertical, clouds are assumed to fill the
layer. The sum of these fractions may exceed one. See [CLOUD](#CLOUD)
for the single fraction used in the radiation calculations.

**CLOUD:** The horizontal fractional cloud cover for each layer. In the
vertical, clouds are assumed to fill the layer. This fraction is the
combination of the model's predicted large-scale and convective
fractions that is used for radiative purposes. See [CLDTOT](#CLDHIGH)
for a description of how these fractions are overlapped in the radiation
calculations.

**CMFMC:** The total vertical convective mass flux through levels
between model layers (edges), in kg m-2 s-1. This is produced by the
convection parameterization (RAS) and it includes the mass flux due to
all cloud types crossing the level. Constituent transport due to these
fluxes can be computed off-line as described in [DTRAIN](#DTRAIN)

**DELP:** Pressure thickness of model layers, in Pa. See [PLE](#PLE).
The layer mass is **DELP / 9.81** kg m-2.

**DDPDTANA**: Tendency of the layer's pressure thickness due to
analysis, in Pa s^-1^[]{#dqrccon .anchor}. The GSI analyzes the surface
pressure and this is the vertical distribution of that mass increment.

**DQRCON, DQRLSC, DQRANV:** The layer production rate of precipitating
condensate from convective, large-scale, and anvil clouds, per unit
horizontal area, in kg m-2 s-1. They include both liquid and frozen
precipitating condensate, but not the production of cloud condensates.

**DQVDTMST, DQLDTMST, DQIDTMST:** Tendency of vapor, liquid and ice
water due to moist processes, in kg kg-1 s-1. This includes the effects
of the convection parameterization (RAS) and all other effects from the
cloud microphysics and large scale and anvil precipitation schemes.

**DQVDTDYN:** Tendency of water vapor due to resolved dynamics, in kg
kg-1 s-1.

**DQVDTTRB:** Tendency of water vapor due to turbulence, including
surface evaporation,\
in kg kg-1 s-1.

**DTDTANA:** The analysis tendency introduced during the corrector
segment of the IAU cycle, in K s-1.

**DTDTDYN:** Temperature tendency due to dynamics, including the
spurrious frictional dissipation of kinetic energy by numerical
processes, in K s-1.

**DTDTFRI:** Temperature tendency due to the frictional dissipation of
kinetic energy by turbulence, including surface friction, in K s-1. It
does not include dissipation from gravity wave drag or the implicit
dissipation in the model's dynamics.

**DTDTGWD:** Temperature tendency due to the frictional dissipation of
kinetic energy by gravity wave drag, in K s-1.

**DTDTLWR, DTDTLWRCLR:** Temperature tendency due to terrestrial
(longwave) radiation for all-sky and clear-sky conditions, in K s-1.

**DTDTMST:** Temperature tendency due to moist processes, in K s-1.

**DTDTSWR, DTDTSWRCLR:** Temperature tendency due to solar (shortwave)
radiation for all-sky and clear-sky conditions, in K s-1.

**DTDTTOT:** The total diabatic temperature tendency for the model
layers, in K s-1 . It is the same as the sum
**DTDTFRI+DTDTGWD+DTDTLWR+DTDTSWR+DTDTMST+DTDTTRB,** and in the
long-term mean should balance [DTDTDYN](#DTDTDYN).

**DTDTTRB:** Temperature tendency due to turbulence, including surface
sensible heat flux, but not including the heating due to frictional
dissipation (see [DTDTFRI](#DTDTFRI)), in K s-1. Above the surface it
includes the diffusive effects due to the Louis and Lock turbulence
schemes (see [KH](#KH)).

**DTRAIN:** The total detrained convective mass flux into each model
layer, in kg m^-2^ s^-1^. This is produced by the convection
parameterization (RAS). The total entrainment mass, *E*, due to all
clouds crossing a layer can be computed from
$E = \delta_{Z}\text{CMFMC - DTRAIN}$, where
$\delta_{Z}\text{CMFMC } \equiv \text{  CMFMC}_{\text{L-1/2}} - \text{CMFMC}_{L + \text{1/2}}$.

**DUDTDYN, DVDTDYN:** Eastward (zonal) and northward (meridional) wind
tendency due to dynamics, in m s-2.

**DUDTGWD, DVDTGWD:** Eastward (zonal) and northward (meridional) wind
tendencies due to gravity wave drag, in m s-2.

**DUDTMST, DVDTMST:** Eastward (zonal) and northward (meridional) wind
tendencies due to moist processes, in m s-2. Currently this represents
the "cumulus friction" effect of mixing momentum in a conservative way,
using the convective mass fluxes from RAS.

**DUDTTRB, DVDTTRB:** Eastward (zonal) and northward (meridional) wind
tendencies due to turbulent processes, in m s-2. This includes surface
friction. Above the surface, it includes the diffusive effects due to
the Louis and Lock turbulence schemes (see [KM](#KH)).

**H**: Geopotential height, in m. It is simply the height,
$\frac{\phi}{g}$, interpolated linearly in $\text{log}(p)$from the
model's edge levels to the desired pressure level. The model's edge
heights are computed using the hydrostatic equation:
$\frac{1}{g}($PHIS +
c~P~$\sum_{l = L}^{\text{LM}}{}\theta_{v}\Delta P)$**,** where
$\Delta P$is the difference in
$\left( \frac{p}{p_{o}} \right)^{\kappa}$at the lower and upper edges of
layer $l$, and $\theta_{v}$ is the virtual potential temperature in the
layer.

[]{#KH .anchor}**KH, KM :** Turbulent diffusivity for heat and other
scalars and for momentum, in m2 s -1. This is defined at the layer
edges, beginning at the top, where it is zero. At the surface
([LM](#LM)+1) it is set .......... It includes the diffusive effects due
to the Louis and Lock turbulence schemes.

**MFX, MFY,** []{#MFZ .anchor}**MFZ:** The eastward and northward
pressure weighted velocity components, in Pa m2 s-1, and the vertical
component of the large-scale mass flux at the layer edges, in kg m-2
s-1. **MF\[X,Y\] =**
$\lbrack u_{c}\Delta y,v_{c}\Delta x\rbrack\delta_{z}p$ **,** where
$\lbrack u_{c},v_{c}\rbrack$ are the velocity components as defined by
the dynamical core on the Arakawa C grid and
$\lbrack\Delta y,\Delta x\rbrack = \lbrack a\Delta\phi,a\text{cos}(\phi)\Delta\lambda\rbrack$
are the meridional and zonal grid spacings, in meters.. These cannot be
computed from **UC** and **VC** and the pressures because the time
average of the product is done over every step taken by the core, so
that the following continuity equation is exactly satisfied.

$\frac{\partial(\text{DELP})}{\partial t}\text{ = } - \frac{1}{\text{AREA}}\lbrack\delta_{i}(\text{MFX})\text{ + }\delta_{j}(\text{MFY})\rbrack - {g\delta}_{k}\text{MFZ} + \text{DDPDTANA}$.

**OMEGA:** The kinematic vertical pressure velocity estimated by the
Finite-Volume dynamics. It is defined for the layers, not the edges. For
layer *l*, it is discretized vertically as
$w_{l} = \left( \overline{\frac{¶p}{¶t}} + \overline{\overset{\cdot}{h}\frac{¶p}{\text{¶h}}} \right)_{l} + (V\text{·Ñ}\overline{p})_{l}$,
where the pressure is defined at the layer edges and the overbar
indicates the average of the layer's upper and lower edges.

**PL:** The layer pressure defined as the average of the upper and lower
edge pressures, [PLE](#PLE)**,** in Pa (see [DELP](#DELP)).

**PLE:** The time-averaged pressure at the upper edge of a layer**.
PLE** = [PS](#PS) **+** $\sum_{l = L}^{\text{LM}}{}$[DELP](#DELP) ~l~.
This is the preferred way of obtaining edge pressures in
lcv-coordinates, rather than relying on the model's hybrid-sigma
coordinate system (i.e., the **AK**s **A**~k~s and **BK**s**B**~k~s),
which may change in future releases.

[]{#PFLCU .anchor}**PFLCU, PFICU, PFLLSAN, PFILSAN:** Downward flux of
precipitating liquid and ice condensate from convective and combined
anvil and large-scale clouds, in kg m-2 sec-1.

[]{#PV .anchor}**PV**: The Ertel's potential vorticity, approximated as
$g(V + f)\frac{¶\text{ln}(q_{v})}{¶p}$, in m2 kg-1 sec-1. Here, $V$is
the vertical component of relative vorticity,, $f$is the Coriolis
parameter, and $q_{v}$ is the virtual potential temperature., Note the
definition in terms of entropy instead of potential temperature and the
neglect of the part associated with the horizontal components of
vorticity.

[]{#QL .anchor}**QL, QI:** The liquid and ice cloud condensate mixing
ratios. These are grid-averaged, not in-cloud, values. They include
condensate produced by both large-scale condensation and that detrained
from convective clouds. They *do not* include the condensate within
convective updrafts.

[]{#QLLS .anchor}**QLLS, QILS, QLAN, QIAN, QCCU:** The liquid and ice
cloud condensate mixing ratios. These are grid-averaged, not in-cloud,
values. These are the separate contributions from ice and liquid, anvil
and large-scale clouds predicted by the model. **QCCU** is a diagnostic
estimate of the total condensate in convective updrafts; it does not
enter any model calculations, but may be useful in comparing with
satellite data.

[]{#REEVAP .anchor}**REEVAP:** Total re-evaporation of all precipitating
condensates, in kg m-2 sec-1.

[]{#TAUCLI .anchor}**TAUCLI, TAUCLW:** Each layer's total cloud optical
thickness in the visible (0.40 to 0.69 micron band), for ice clouds and
liquid water clouds, respectively.

**TAUIR:** Total (liquid + ice) in-cloud optical thickness in the
infrared (540-980 cm-1 band).

## F.2 Two-dimensional Fields 

**ALBEDO:** The time-averaged surface albedo defined as the ratio of the
time-averaged incident and reflected fluxes and should satisfy **ALBEDO
=** [SWGDWN](#SWGDWN)**/(SWGDWN-**[SWGNET](#SWGNET)**).** At night
points, this is set to [\_FillValue](#FillValue).

**ALBVISDF, ALBVISDR, ALBNIRDF, ALBNIRDR:** The direct (beam) and
diffuse albedos for the "visible" (the GCM uses the same albedos for the
UV and the PAR spectral regions----0.175 to 0.69 microns) and the
"near-infrared" (0.69 to 3.85 microns). These are simply time-averaged
surface properties, but are defined only where there was daylight at the
point during the averaging interval. They do not correspond to the
ratios of time-averaged incident and reflected fluxes.

**BSTAR:** The bouyancy scale of the surface layer in m s-2. It is
defined as $\frac{g}{\rho_{a}u^{}}\frac{F_{S_{v}}}{c_{P}T_{a}}$, where
$\rho_{a}$ is the near-surface air density ([RHOA](#RHOA)) and $T_{a}$
the near-surface air temperature, $u^{}$ is the friction velocity
([USTAR](#USTAR)), and $F_{S_{v}}$ is the surface flux of virtual dry
static energy in W m-2, $F_{S_{v}}$ = ([HFLUX](#HFLUX) +
$(1 - e)$[EFLUX](#EFLUX)**).**

**CLDHGH, CLDMID, CLDLOW, CLDTOT:** High, middle, low, and total
cloudiness. The high, middle, low level values correspond to the three
superlayers used in the GEOS-5 solar and terrestrial radiation
parameterizations. Clouds within these superlayers are assumed to be
maximally overlapped. High clouds are those occuringoccurring above
roughly 400 hPa and low clouds are those occuringoccurring below 700
hPa, although the groupings are done ion the model's terrain following
coordinate and so the bounding pressures will differ significantly from
these values over high topography. The model assumes that the overlapped
between the superlayers is random, and the total cloudiness uses this
assumption. The total cloudiness is computed each time the radiation is
called, and so its time mean cannot be exactly constructed from the
time-mean cloudiness in the three super layers.

**CLDPRS, CLDTMP:** The cloud-top temperature and pressure of the first
cloud "seen" from above at 540-980 cm-1 in the infrared. Clouds are
visible if in-cloud (not layer) optical thickness in this band exceeds
0.14, independent of their fractional areal coverage.

**DISPH:** Surface displacementy height in meters. See the description
of the neutral drag coefficient.

**DTG:** Change in surface temperature during the averaging interval in
deg K. This refers to the area-mean surface temperature under each
atmospheric column, and so, it may contain contributions from land-,
water-, and ice-covered parts of the grid box.

**EFLUX:** The upward turbulent flux of latent heat flux at the surface,
in W m-2. This includes the latent heat relative to liquid of all
turbulent moisture fluxes through the surface (see [EVAP](#EVAP)**)**.

**EMIS:** The surface emissivity. This is areally averaged over all
surface tiles and is constant in time.

**EVAP:** Evaporation in kg m-2 s-1., a Actually the total turbulent
flux of water vapor at the surface, including fluxes from transpiration,
sublimation, and surface condensation. The turbulent flux of could cloud
condensate (fog) is assumed to be zero. .

**FRLAKE, FRLAND, FRLANDICE, FROCEAN:** GEOS-5 uses these four primary
surface types and these are their fractions under each atmospheric
column.

**GRN:** The "greenness" or fraction of transpiring leaves averaged over
the land areas of a grid box. If there are several vegetation tiles
within the land part of a grid box, the average is **LAI** weighted.
**GRN** is set to [\_FillValue](#FillValue) where [FRLAND](#FRLAKE) = 0.

**GWETROOT, GWETTOP:** The degree of saturation or "wetness" in the
root-zone (top meter of soil) and top soil layer (top 2 cm). These are
defined as the ratio of the volumetric soil moisture to the porosity.
These quantities are set to [\_FillValue](#FillValue) where
[FRLAND](#FRLAKE) = 0. Elsewhere they are time-mean and area-mean values
of the ratio over the land part of the grid box.

**HFLUX:** The upward turbulent sensible heat flux at the surface, in W
m-2.

**LAI:** The areal average of the leaf-area index over all land parts of
a grid box. **LAI** is set to [\_FillValue](#FillValue) where
[FRLAND](#FRLAKE) = 0.

**LWGDWN, LWGDWNCLR:** The all-sky and cloud-free fluxes of downwelling
terrestrial (longwave) radiation at the surface in W m-2.

**LWGNET:** The net downward flux of terrestrial (longwave) radiation at
the surface in W m-2. This is identical to **LWGDWN- LWGUP.**

**LWGUP:** The all-sky upwelling terrestrial (longwave) radiation at the
surface, in W m-2. This includes both the surface emmission and the
reflection..

**LWI:** A Land-Water-Ice mask provided for backward compatibility with
the GEOS-4 product. It is 1 over continental areas, 0 over open ocean,
and 2 over sea-ice covered ocean. Since in GEOS-5 a grid box can be a
combination of these, continental areas are arbitrarily defined as those
where [FRLAND+FRLANDICE](#FRLAKE)**\>=≥0.5.** The remaining grid boxes
are designated as sea-ice if the ice cover exceeds 50%; otherwise they
are open (ice-free) ocean.

**LWTUP, LWTUPCLR:** Outgoing longwave (terrestrial) radiation at the
top of the model's atmosphere (currently 0.01 hPa) for all-sky and
clear-sky conditions, in W m-2.

**PARDF, PARDR, NIRDR, NIRDF:** Incident flux of of diffuse and direct
PAR and NIR at the surface, in W m-2. PAR is defined as the solar
radiation between 0.4 and 0.69 microns. NIR is the solar near- infrared,
defined as the solar radiation between 0.69 and 3.85 microns. These are
scaled so that the total solar flux is accounted for in a band from
0.175 to 3.85 microns.

**PBLH:** Height above the surface of the planetary boundary layer in
meters. This is obtained diagnostically at every time step from the heat
diffusivity in the model layers. It is defined as the height of the
lowest layer in which the diffusivity falls below 2 m2 s-1. Where no
layer is above this value, the boundary layer height is set to the
height of the surface layer.

**PHIS:** The surface geopotential, $\text{gh}_{s}$, in m-2 s-2. Here
$h_{s}$is the height of the surface above sea level, and $g$ m s-2.

**PRECANV, PRECLSC, PRECCON:** the large-scale precipitation from
anvils, the non-anvil large-scale precipitation, and the convective
precipitation, in kg m-2 s-1. These include both rainfall and snowfall.

**PRECTOT:** The total precipitation (**PRECANV+PRECLSC+PRECCON**) in kg
m-2 s-1.

**PRECSNO:** The "snowfall" includes all frozen precipitation, in kg m-2
s-1.

**PS:** The surface pressure in Pa. The height at this pressure can be
obtained from the surface geopotential [PHIS](#PHIS)**.** The total
atmospheric mass is $\frac{1}{g}$**PS** kg m-2.

**QV10M, QV2M:** The specific humidity at 10 m and 2m above the
displacement height ([DISPH](#DISPH)) in the surface layer, in kg kg-1.

**REEVAP:** Total re-evaporation of precipitating condensate, in kg m-2
s-1. Includes evaporation and sublimation and is the total contribution
from all three cloud types.

**RH**: The relative humidity. This is approximated by q/qs where q is
the specific humidity and qs is its saturated value. The saturated value
is computed over liquid for temperatures above 273.16K and over ice for
temperatures below 253.16K. At intermediate temperatures the values over
liquid and ice are averaged with weights that vary linearly with
temperature.

**RHOA:** Surface air density in the lowest model layer, in kg m-3. This
is the density used in bulk formulasformulae.

**SGH**: The isotropic standard deviation of topography used for the
subgrid-scale gravity wave drag parameterization, in m. Currently the
effect of orographic gravity waves is independent of the angle between
the flow and the orographic ridges, so only this isotropic component is
relevant.

**SLP:** The surface pressure reduced to sea level, in Pa. Over
topography the reduction is done by assuming a lapse rate of 6.5 K km-1
from a free atmospheric temperature, which is currently taken as the
lowest model layer above 150 hPa above the surface.

**SNOMAS:** The mass of snow per unit of ice-free land area
([FRLAND](#FRLAKE)), in kg m-2. In grid boxes with no land it is set to
[\_FillValue](#FillValue)**.** Over other land areas it represents an
average over the non-glaciated part.

**SNODP:** The geometric snow depth in meters. This accounts for packing
and aging of the snow.

[]{#SWGDN .anchor}**SWGDN, SWGDNCLR, SWTDN**: Incident solar radiation
(0.175 to 3.85 microns) at the surface for all-sky and clear-sky
conditions and the top of the atmosphere, in W m-2. Since we do a single
atmospheric radiative transfer calculation in a grid box, we assume the
incident radiation is the same for all surface tiles within the box.
MERRA uses a solar constant of 1365 W m-2.

[]{#SWGNT .anchor}**SWGNT, SWGNTCLR, SWGNTCLN, SWGNTCLRCLN, SWTNT,
SWTNTCLR, SWTNTCLN, SWTNTCLRCLN:** Net downward flux of solar radiation
at the surface and the top of the model's atmosphere (0.01 hPa) averaged
over all land tiles for all-sky, clear-sky, clean-sky, and
clear-clean-sky conditions, in W m-2. The term "clean-sky" refers to
fluxes computed with the aerosol loading set to zero.

**TAUGWX, TAUGWY:** The eastward (zonal) and northward (meridional)
components of the atmospheric stress on the surface due to atmospheric
gravity wave drag, in N m-2.

**TAUHGH, TAUMID, TAULOW, TAUTOT:** Total cloud optical thickness in the
0.40 to 0.69 micron band for the high, middle, and low cloud regions
(see [CLDHGH](#CLDHIGH)**)** and for the entire column.

**TAUX, TAUY:** The eastward (zonal) and northward (meridional)
components of the atmospheric frictional stress on the surface, in N
m-2.

**TO3 :** The vertically integrated ozone, in Dobson units.

**TPW, TQV:** The vertically integrated water vapor in the column, in kg
m-2.. These are synonyms.

**TQL, TQI:** The vertically integrated liquid and ice water in the
column, in kg m-2.

**TROPP:** The tropopause pressure in Pa. The tropopause pressure is
defined as the pressure where the function
$\alpha T(p) - \text{log}_{\text{10}}p$ reaches its first minimum above
the surface. Here $\alpha = 0\text{.}\text{03}$ and $p$ is in hPa. If no
minimum is found between 550 hPa and 40 hPa, **TROPP** is set to
[\_FillValue](#FillValue)**.**

**TROPQ:** The tropopause specific humidity in kg kg-1. The tropopause
is defined as in **TROPP.**

**TROPT:** The tropopause temperature in K. The tropopause is defined as
in **TROPP.**

**TSRAD:** The area weighted skin temperature of all surface tiles in a
grid box, in K. This is the skin temperature used for radiation.

**TTO3:** The vertically integrated ozone in the troposphere, in Dobson
units. The troposphere is defined as all levels below [TROPP](#TROPP)**.
TTO3** and **TROPP** are computed at every time step and averaged
separately.

**U50M, U10M, U2M, V50M, V10M, V2M:** The eastward and northward wind
component at 50m, 10 m, and 2m in the surface layer, in m s-1. The 2m
and 10m values are defined above displacement height ([DISPH](#DISPH)),
the 50m values are above the surface.

**USTAR:** The surface friction velocity,
$u^{} = \sqrt{\frac{|t|}{\rho_{a}}}$, in m s-1. This mean quantity is
formed by doing the the areal average over the surface tiles in a grid
box instantaneously to $|t|$ , and the time averaging on $u^{}$ itself.
It is thus not exactly what would be obtained from [TAUX,
TAUY](#TAUX)**,** and [RHOA](#RHOA)**.**

**Z0H:** The surface roughness for heat, in m.

**Z0M:** The dynamic surface roughness, in m.

#  

# Appendix G: Surface Representation

In GEOS-5 the surface below each atmospheric column consists of a set of
tiles that represent various surface types. Tiles can be of four
different types: Ocean, Land, Ice, Lake, as illustrated in the figure.
In each grid box a single Ice tile represents those areas covered by
permanent ice. Similarly a single Lake tile represents continental areas
covered permanently by water. Other continental areas (non Lake or Ice)
can be further subdivided into tiles that represent parts of the grid
box in different hydrological catchments, defined according to the
Pfaffsteter (19xx) system. Each of these is, in turn, divided into
subtiles (not shown in figure) that represent the wilted, unsaturated,
saturated, and snow-covered fractions of the tile. These fractions vary
with time and are predicted by the model based on the hydrological state
of the catchment and its fine-scale topographic statistics. Details of
the land model, including the partitioning into subtiles, can be found
in Koster et al. (2001). The Ocean tile can be divided into two subtiles
that represent the ice-covered and ice-free parts of the ocean part of
the atmospheric grid box. The fractional cover of these subtiles also
varies with time. In MERRA, the fractional cover of sea ice and the
ocean surface temperature are specified from the climatology of Reynolds
and Smith (19xx).

![](media/image3.png){width="4.03125in" height="3.5416666666666665in"}

# Appendix H: Budgets

As described in [Appendix A](#_Appendix_A:_The), the concatenation of
the IAU corrector segments of each analysis cycle is equivalent to a
single, continuous run of the AGCM with an additional term--the analysis
tendency--on the right hand side of all equations that predict analyzed
quantities. Budgets in MERRA are thus identical to those in the
free-running AGCM, with the addition of the effects of analysis
tendencies, which are constant during the six-hour duration of each
corrector segment.

In the MERRA output we produce a full accounting for seven atmospheric
quantities: kinetic energy, the enthalpy of moist air, the mass of the
atmosphere, the mass of water in vapor, liquid, and ice forms, and the
total mass of odd oxygen.. We also keep exact budgets for XX land
surface quantities:......

An exact accounting for each of the seven atmospheric quantities is kept
in two file collections: [inst1_2d_int_Nx](#inst1_2d_int_nx) and
[tavg1_2d_int_Nx](#tavg1_2d_int_nx). Both collections consist of
2-dimensional data on the model's native horizontal grid, and both
contain only vertical integrals. The first contains instantaneous
vertical integrals of the seven quantities at the beginning of each hour
(i.e., 00:00Z, 01:00Z, etc). The second collection contains various
hourly-mean, vertically-integrated contributions to the tendencies of
each of the seven quantities. This Appendix explains how these
contributions can be combined to produce the local change in the
quantity implied by values in the [inst1_2d_int_Nx](#inst1_2d_int_nx)
collection, how the contributions were computed, and what assumptions
enter this accounting.

In the following, we will denote the vertical mass-weighted integrals of
quantities by an overbar:

$\text{  }\overline{X} = \int_{p_{T}}^{p_{S}}X\frac{\text{dp}}{g}$,

where $p_{S}$ is the surface pressure, and $p_{T}$ is the pressure at
the top of the model's atmosphere (1 Pa).

***Atmospheric Mass*** The spatial distribution of the total atmospheric
mass, $M = (p_{S} - p_{T}\frac{)}{g}$, is stored in the variable
**MASS** in the [inst1_2d_int_Nx](#inst1_2d_int_nx) collection. In the
[tavg1_2d_int_Nx](#tavg1_2d_int_nx) collection, the total tendency is
separated into contributions from dynamics (**DMDTDYN)**, and analysis
(**DMDTANA)**. The finite-volume dynamics used in GEOS-5 conserves mass
to within round-off at 64-bit precision, so the global mean of
**DMDTDYN** is effectively zero. The physics used in the GEOS-5 AGCM
does not include changes in column mass due to changes in water content;
there is, therefore, no physics contribution. Although the atmospheric
physics does not include atmospheric water in its mass budget, realistic
changes in atmospheric mass can still occur since the surface pressure
is analyzed and surface pressure observations include the effect.. Mass
changes due to water content thus appear as analysis increments rather
than physics increments. It is not clear how much improvement in the
mass budget, as measured, say, by the degree of invariance of dry mass,
would be achieved if the atmospheric model had a more complete
treatment. \[WE CAN INCLUDE A FOUR PANEL FIGURE HERE FOR ONE YEAR FROM
THE MOST RECENT SCOUT RUN SHOWING THE HOURLY MASS IN ONE PANEL AND THE
TENDENCY THE TWO CONTRIBUTIONS AND THEIR SUM IN THE ANOTHER PANEL. TWO
OTHER PANELS COULD BE THE SAME THING FOR THE MEAN DIURNAL CYCLE.\]

***Kinetic Energy*** The instantaneous total kinetic energy for each
grid column,
$K = \overline{\frac{1}{2}\left| \overrightarrow{v} \right|^{2}}$
***,*** is stored in the variable **KE** in the
[inst1_2d_int_Nx](#inst1_2d_int_nx) collection. In the
[tavg1_2d_int_Nx](#tavg1_2d_int_nx) collection, the total tendency is
first separated into contributions from dynamics (**DKEDTDYN)**, physics
(**DKEDTPHY)**, and analysis (**DKEDTANA)** increments of winds and
atmospheric masses.

$\frac{\partial K}{\partial t} = \left\lbrack \frac{\partial K}{\partial t} \right\rbrack_{\text{DYN}} + \left\lbrack \frac{\partial K}{\partial t} \right\rbrack_{\text{PHY}} + \left\lbrack \frac{\partial K}{\partial t} \right\rbrack_{\text{ANA}}$
(1)

The sum of the three contributions obtained from the
[tavg1_2d_int_Nx](#tavg1_2d_int_nx) collection exactly matches the
difference of values in the [inst1_2d_int_Nx](#inst1_2d_int_nx), since
the contributions are computed by differencing $K$ before and after each
process is included. For example,

$\text{KE}_{\text{1:00Z}} - \text{ KE}_{\text{0:00Z}} = \text{ 3600}\text{.}(\text{DKEDTDYN } + \text{ DKEDTDYN } + \text{ DKEDTDYN})_{\text{0:30Z}}$**.**

The dynamical contribution can be further divided by considering the
vertically integrated kinetic energy equation written in flux form.
Ignoring contributions from the analysis and from explicit frictional
processes that are included in the physics, this is:

$\left\lbrack \frac{\partial K}{\partial t} \right\rbrack_{\text{DYN}} = - \nabla \cdot (\overline{\overrightarrow{v}\frac{1}{2}\left| \overrightarrow{v} \right|^{2}}) - \nabla \cdot (\overline{\overrightarrow{v}\varphi}) - \overline{\text{ωα}} - \frac{\partial}{\partial t}(\varphi_{S}p_{S}) - \frac{\partial}{\partial t}(\varphi_{T}p_{T}) - \overline{R_{\text{DYN}}}$
(2)

The first two terms on the right hand side of (1) are the divergence of
the vertically integrated kinetic energy and geopotential fluxes. The
third term, which appears with opposite sign in the thermodynamic
equation, is the conversion between kinetic and total potential energy.
The fifth term is the change in gravitational potential energy
associated with raising the mass in the column from sea-level to the
local height of the surface topography. The sixth term is the change in
gravitational potential energy of the mass above the model top (1 Pa or
about 0.1 kg m^-2^) at the height of the top rises and falls. The last
term groups all spurious contributions from the discretization of the
equation.

The numerics of finite volume dynamical core used in GEOS-5 do not
naturally conserve total energy (Lin 200x). This is so for several
reasons:

First the advection of the flow field produces numerical dissipation and
so does not conserve kinetic energy. Some numerical dissipation is
present in all discrete formulations of the dynamics useful for
long-term integrations. Even conservative formulations, such as spectral
schemes or centered finite-difference schemes like those based on the
Arakawa Jacobians, need to be supplemented by explicit dissipation from
horizontal diffusion or filters applied to the flow. In the finite
volume dynamical core, the dissipation is not added explicitly and so is
harder to track.

A second spurious tendency of total energy comes from the form of the
pressure gradient force and the discretization of the thermodynamic
equation.. In the continuous equations, the vertical integral of the
rate of work done by the pressure gradient force is represented by
second through fifth terms in the above equation with the
$\overline{\text{ωα}}$ term being identical to the corresponding term in
the thermodynamic equation. This also is not true in the discrete core.

A third spurious contribution comes from time-truncation errors. This
arises because the state variables that are directly updated are the
horizontal components of the wind, the surface pressure, and the virtual
potential temperature, while the kinetic and total potential energy
before and after the time step are non-linear combinations of these.

All of these spurious contributions are present even when the core is in
its vertically Lagrangian mode, where all layers are bounded by material
surfaces. Periodically the core returns to hybrid sigma-pressure
coordinates by doing a vertical coordinate transformation or "vertical
remapping". Since this step does not involve any new physics, only a
change in vertical coordinate, it should produce no energy
transformations. The vertical remapping is indeed done to conserve the
sum of internal, gravitational potential, and kinetic energies, but not
the three individually.

To enforce total energy conservation, the core needs to compensate for
all of these spurious sources. It does this by simply computing the
global-mean change in total energy across the entire code and
arbitrarily adding it back as a heating in the thermodynamic equation;
it makes no adjustment to the kinetic energy.

Terms on the right hand side of (2) are stored in the
[tavg1_2d_int_Nx](#tavg1_2d_int_nx) and satisfy

$\text{DKEDTDYN } = \text{ CONVKE } + \text{ CONVPHI } + \text{ KEGEN - PEDYN - DKEDTRESDYN}$**,**

where the first two contributions are the convergence of kinetic energy
and geopotential fluxes, the third is the generation of kinetic
energy,$- \overline{\text{ωα}}$, the fourth is the sum of the two
boundary terms, and the fifth is the total spurious contribution
computed as a residual. The two convergences are computed diagnostically
using the core's own advection scheme. The conversion term is computed
using a finite difference form of:

$\text{αω} = c_{p}^{d}T_{v}\left( \frac{p}{p_{0}} \right)^{\kappa}\frac{d}{\text{dt}}\left( \frac{p}{p_{0}} \right)^{- \kappa}$,

which corresponds closely to the form that appears in the core's
potential-temperature-based thermodynamic equation. \[HERE WE CAN PUT I
A COUPLE OF FIGURES SHOWING THE BREAKDOWN OF THE KE BUDGET THUS FAR,;
BOTH LINE PLOTS AND HORIZONTAL PLOTS.\]

\[IF WE SUCCEED IN A BETTER ATTRIBUTION OF THE RESIDUAL OF THE DYNAMICS
CONTRIBUTION TO THE KE BUDGET, THAT DISCUSSION GOES HERE.\]

The vertically integrated physics contribution to the kinetic energy
tendency consists of frictional effects due to subgrid-scale motions. It
can be separated into contributions due to turbulence, including all
boundary layer friction, to vertical mixing of momentum by the
convective parameterization, and to the friction associated with gravity
wave drag. Since the GEOS-5 physics does not time split the effects of
these three processes, there is some time truncation in the separation,
and this is stored as a residual.

$\text{DKEDTPHY } = \text{ DKEDTGWD } + \text{ DKEDTMST } + \text{ DKEDTTRB -DKEDTRESPHY}$**,**

$$\left\lbrack \frac{\partial K}{\partial t} \right\rbrack_{\text{PHY}} = - \overline{D_{\text{GWD}}} - \overline{D_{\text{TRB}}} - \overline{D_{\text{MST}}} - \overline{R_{\text{PHY}}}$$

$$

# References 

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Pfaffsteter

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Reynolds and Smith or Hadley??

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# Web Resources

[]{#APPENDIXC .anchor}GMAO web site: <http://gmao.gsfc.nasa.gov/>

GMAO Operations page: <http://gmao.gsfc.nasa.gov/operations/>

[]{#CF .anchor}CF Standard Description:
<http://www.cgd.ucar.edu/cms/eaton/cf-metadata/CF-current.html>

CF Standard Names:
<http://www.cgd.ucar.edu/cms/eaton/cf-metadata/standard_name.xml>

NCSA, 1999: The NCSA HDF Home Page. <http://hdf.ncsa.uiuc.edu/>

NASA, 1999: HDF-EOS Standards.
[http://hdfeos.gsfc.nasa.gov/](http://hdfeos.gsfc.nasa.gov/ )

[]{#_5._File_Naming_Conventions .anchor}