Increasing the Interoperability of an Earth System Model:

Atmospheric-Ocean Dynamics and Tracer Transports

NCC4-624

Milestone C: FY03 Annual Report

February 2003 -- March 2004

1.  Project Objectives

> The objectives of this project are twofold:

1.1 Demonstrate interoperability at the model level using the ESM (Earth
System Model) Framework (ESMF). Build a demonstration ESM using the
AGCM/OGCM and/or components developed by other modeling teams supported
by this CAN.

2.  Estimate the sensitivity of simulated El Niño/Southern Oscillation
    structures to different background states of the coupled
    ocean-atmosphere system, including testing the impact of NASA data
    in improving El Niño predictions.

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2.  Approach

For Objective 1.1, the approach is based on designing interfaces between
the ESMF and an expanded version of the UCLA ESM, including components
developed by other groups. Towards this objective, C. Roberto Mechoso
(PI) and Joseph Spahr visited Cecelia Deluca and members of the ESMF
Development Team at NCAR on November 20 and 21, 2003, in order to
discuss issues related to the ESM codes and their future interface to
the ESMF.

The sensitivity study referred to in Objective 1.2 will be performed
with the UCLA AGCM/LANL POP combination, and the testing with UCLA
AGCM/MIT OGCM combination. The latter will build on work at the JPL
Ocean Data Assimilation Project. John Baumgardner (co-PI) is part of the
team at LANL that develops the POP version with a hybrid vertical
coordinate (HYPOP). Dimitris Menemenlis (Co-PI) contributes his
expertise with the MIT OGCM.

3.  Scientific Accomplishments

3.1 Coupling of the UCLA AGCM and MIT OGCM

**The UCLA AGCM has been coupled to the MIT OGCM and a number of test
integrations have been carried out both in coarse resolution and in
high-resolution configurations.**

The coarse-resolution UCLA AGCM (version 7.2p) is global, has 16
vertical levels, and the horizontal grid spacing is 5 deg. lon x 4 deg.
lat. The high-resolution AGCM has 30 vertical levels and the horizontal
grid spacing is 2.5 deg. long. x 2 deg. lat. The coarse-resolution MIT
OGCM (version release1) spans 80S to 80N, has 15 vertical levels, and
the horizontal grid spacing is 4 deg. both zonally and meridionally. The
high-resolution OGCM spans 73S to 73N and it has 46 vertical levels. The
horizontal grid spacing is 1 deg. in longitude. Meridionally, the grid
spacing is also 1 deg. outside the tropics but decreases to 1/3 deg.
near the Equator for improved resolution of equatorial processes. The
model configuration is the same as that used for quasi-real-time ocean
circulation analyses by the ECCO consortium
(http://ecco.jpl.nasa.gov/external/).

![](media/image1.wmf){width="6.496527777777778in"
height="4.9534722222222225in"}

Figure 1. Monthly-mean simulated SSTs (C) for April (left column) and
October (right column) at the beginning (year 1, top row) and end (year
32, middle row) of the simulation performed, and their difference
(bottom row)

Figure 1 shows the monthly-mean simulated SSTs for April and October at
the beginning (year 1) and end of the simulation performed (year 32).
The results are encouraging with a much better developed equatorial cold
tongue in October than in April, as in the observation. The development
of a cold bias is evident in the tropics while a warm bias develops in
the high latitudes of the Southern Hemisphere.

![](media/image2.wmf){width="6.488194444444445in"
height="4.867361111111111in"}

Figure 2. Deviations from the annual mean of the monthly-mean simulated
SSTs (C) for at the beginning (year 1, top panel) and end (year 32,
middle panel) of the simulation performed, and their difference (bottom
panel)

Figure 2 shows the seasonal cycle (annual mean removed) at the equator
simulated by the model at the beginning and end of the simulation, as
well as the difference between these two fields. There is a clear
dominance of the annual component at the beginning (as observed). Later
in the simulation, a semiannual component appears.

We have verified that the model produces a significant interannual
variability. Nevertheless, a time series analysis for a selected
location on the equator (Nino 3) reveals that the dominant signal has a
quasi-biennial period, and a smaller peak in the quasi-quadrennial
periods (ENSO).

3.2 Upgrade of the PBL parameterization

**The parameterization of the planetary boundary layer (PBL) used in the
AGCM was upgraded to a version with multiple layers without loss of
performance compared to the one in Milestone E. Scaling curves were
provided and the documented source code was made publicly available via
the Web**.

In the UCLA Earth System Model (ESM) version with which we started this
project, the atmospheric component (UCLA atmospheric general circulation
model, AGCM) includes a variant of the bulk parameterization for the
variable-depth PBL processes proposed by Deardorff (1972). This is
relatively simpler and physically realistic. In the model, the layer
next to the lower boundary is designated as the variable-depth PBL and
is assumed to act as a well-mixed layer (Suarez et al. 1983).

Unlike the single-layer approach, the hybrid multi-layer
parameterization allows for vertical shears and deviations from
well-mixed profiles within the PBL. These deviations are expected to be
small for thermodynamic conservative variables on a convectively active
PBL, while they can be significantly large for a convectively inactive
PBL. The formulation of processes highly concentrated near the PBL top
remains tractable in this approach, while it is more directly applicable
to a variety of PBL regimes, particularly the diurnally changing PBL
over land.

The single and multiple layer PBL parameterizations appear as options to
be set up at run time. The component of the code directly affected by
the changes is AGCM-Dynamics. The AGCM-Physics part of the code is
unchanged. A composite single layer PBL is computed from the multilayer
PBL, and computation of physical column processes other than those of
the PBL takes place as before.

Figure 3 shows the simulated January-mean precipitation, which compares
reasonably well with the observed distribution.

![](media/image3.wmf){width="5.993055555555555in"
height="2.9722222222222223in"}

Figure 3: January mean precipitation simulated using the multilayer PBL.
Contour interval is 2mm/day

3.3 Development of HYPOP

HYPOP is a next-generation global ocean model that features an arbitrary
Lagrangian-Eulerian (ALE) treatment in the vertical grid direction. This
feature allows the computational grid to conform to potential density
surfaces in the deeper ocean while simultaneously resolving the mixed
layer near the ocean surface with horizontal layers of nearly uniform
thickness. Such treatment promises to reduce significantly the spurious
vertical diffusion inherent in current generation Eulerian ocean models
that use uniform thickness layers throughout the ocean volume.

Considerable effort was invested this year in development of a robust
algorithm for splitting the fast barotropic motion, corresponding to
external gravity wave oscillations, from the remaining slower ocean
dynamics in the context of a two time level time stepping approach that
is stable and robust for the strong (unsmoothed) topographical
variations present in the Earth\'s ocean basins. Our scheme bears close
resemblance to the predictor-corrector method of Higdon \[JCP, 177,
59-94, 2002\], but is more efficient in that it requires only one
integration of the barotropic equations over each baroclinic interval.
Like Higdon\'s, our scheme uses a subcycling approach with a small time
step to advance the 2D barotropic system of equations. In slight
contrast to Higdon\'s method, we use total velocity in the layer
equations instead of baroclinic velocity. Also, to enforce consistency
between the barotropic solution and the remaining slower dynamics we
require the sum of the lateral fluxes over all the vertical layers to
match the time-integrated lateral fluxes from the barotropic solution.

The new splitting/time stepping method has been tested against the
Eulerian fixed z-level POP model using real ocean bottom topography and
observed wind forcing and shown to yield stable behavior and similar
results for multi-year integrations. In terms of ease of coupling to
other climate model components, the two time level HYPOP formulation is
simpler than the leapfrog formulation currently employed in POP.

4.  Technology Accomplishments

    1.  The DDB code was upgraded and further developed

The DDB, which was developed in Round 2, is a general-purpose tool for
coupling multiple, possibly heterogeneous, parallel models. Using the
DDB, each producer sends data directly to each consume. This strategy
conserves bandwidth, reduces memory requirements, and minimizes the
delay that would otherwise occur if a centralized element were to
reassemble each of the fields and retransmit them.

The following is a list of DDB code upgrades performed for Milestone I:

a.  Support both PVM and MPI communications.

b.  The DDB checks the input arguments for consistency and valid range.

c.  The DDB configured meta-machine and data flow matrix can be verified
    at the end of registration.

d.  Modified portions of the code to enhance code documentation, remove
    errors, zero out created control data structures, and clarified DDB
    diagnostic output.

e.  Support for 32 and 64 bit addressing modes.

f.  Simplified user interface.

g.  Revised documentation.

    2.  Software Management

The UCLA AGCM and POP versions used in this project are now managed
using the tool Concurrent Versions System (CVS) and are installed in CVS
repositories at UCLA(http://). The MIT GCM, including the modifications
for coupling it to the UCLA atmosphere model, is also being maintained
on CVS servers, both at JPL and at MIT. The MIT server
(http://mitgcm.org/cgi-bin/cvsweb.cgi/MITgcm/) is configured as an
anonymous CVS server, hence making the code modifications and updates
publicly available in real time.

4.5 Project website

The project website was developed and is frequently updated
([www.atmos.ucla.edu/\~mechoso/esm)](http://www.atmos.ucla.edu/~mechoso/esm)).
Milestone reports are posted in the website.

5.  Status/Plans

We are currently working on improving the promising results obtained
with the UCLA AGCM coupled to the MIT OGCM. Specifically, we are using
in the AGCM the upgraded PBL parameterization described in the next
sub-section of this report. This is an important task in view of the El
Niño predictability studies to be performed in the third and last year
of the project.

In regard to HYPOP, current effort is focused on evaluating various
candidate methods for specifying the grid in the vertical direction to
minimize overall numerical error. Although all the candidate methods
yield almost isopycnal treatment in the deep ocean and almost uniform
horizontal layers near the ocean surface where wind stress causes strong
mixing, they differ in how they handle the region in between. While an
abrupt transition from horizontal layers in the mixed layer to nearly
isopycnal layers below the mixed layer might seem to be a simple and
plausible approach, steeply plunging layer geometry typically leads to
large horizontal pressure gradient errors while large layer thicknesses
that frequently arise imply locally poor vertical resolution and hence
significant discretization error. Therefore, some appropriate amount of
horizontal smoothing of the grid is essential. However, identifying
nearly optimal strategies for minimizing overall error is currently a
challenging research question. Regardless of the strategy selected, it
is essential the method be robust, especially at high spatial
resolution. We expect our own evaluation process to be completed soon.
We are also well under way in our effort to create a version of HYPOP
that is ESMF compliant to meet the requirements of this project.

Work has started on the development of a conceptual model of the ESM
embedded in the ESMF.

6.  Point of contact

> C. Roberto Mechoso
>
> Department of Atmospheric Sciences
>
> UCLA Mail Code 156505
>
> 405 Hilgard Avenue
>
> Los Angeles, California 90095

7.  Captions for the Graphics

Figure 1. Monthly-mean simulated SSTs (C) for April (left column) and
October (right column) at the beginning (year 1, top row) and end (year
32, middle row) of the simulation performed, and their difference
(bottom row)

Figure 2. Deviations from the annual mean of the monthly-mean simulated
SSTs (C) for at the beginning (year 1, top panel) and end (year 32,
middle panel) of the simulation performed, and their difference (bottom
panel)

Figure 3: January mean precipitation simulated using the multilayer PBL.
Contour interval is 2mm/day

8.  Publications

> None

9.  Conference Presentations

The UCLA Earth System Model: Applications and Further Developments (with
J. D. Farrara and D. S. Katz). General Assembly of the International
Union of Geodesics and Geophysics, 30 June -- 11 July 11 2003, Sapporo,
Japan.

Earth system modeling at UCLA. Computers in Atmospheric Sciences (CAS)
2003 Meeting, 8-11 September 2003, Annecy, France.

10. Graduate Students and Post Docs

> Gabriel Cazes -- Graduate Researcher
>
> Heng Xiao -- Graduate Student