Gridded Meteorological Data Archives

Overview

The National Weather Service's National Centers for Environmental Prediction (NCEP) runs a series of computer analyses and forecasts operationally. NOAA's Air Resources

Laboratory (ARL) routinely uses NCEP model data for use in air quality transport and dispersion modeling calculations. In 1989 ARL began to archive some of these datasets for

future research studies. ARL has in the past, or is presently archiving the following NCEP datasets, which can be retrieved via ftp by clicking on the name of the dataset.

For further information on model changes see the following web sites:

http://www.nco.ncep.noaa.gov/pmb/

http://www.nco.ncep.noaa.gov/pmb/changes/

http://www.emc.ncep.noaa.gov/mmb/research/eta.log.html

http://www.emc.ncep.noaa.gov/modelinfo/index.html

Currently Available Data

NAM (Eta) Data Assimilation System (EDAS 40km, 2004-)

FTP Data

NOAA ARL FTP Server

Readme file

Latitude/longitude pairs

Recent changes

Missing Data

2014

2013

2012

2011

2011 Alternate archive

2010

2009

2008

2007

Grid domain map

NCEP NAM(Eta)/EDAS and the GCIP Project

GDAS one-degree archive (Dec 2004- )

FTP Data

NOAA NCEP Server (recent files only)

NOAA ARL FTP Server

University of Alaska Fairbanks FTP Server

Details on the NCEP Global Data Assimilation System (GDAS) model

Details on the NCEP Global Forecast System (GFS), the forecast component of the GDAS

Readme file

Missing data listing

Grid domain map

GDAS half-degree archive (Sep. 1, 2007- )

FTP Data

NOAA ARL FTP Server

Details on the NCEP Global Data Assimilation System (GDAS) model

Details on the NCEP Global Forecast System (GFS), the forecast component of the GDAS

Readme file

Missing data listing

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Grid domain map

NCEP/NCAR Reanalysis (1948 - present) - Note: the data are usually only updated at the beginning of the year for the previous year.

FTP Data

NOAA ARL FTP Server

Readme file

NCEP Reanalysis Information Page

NCAR Reanalysis Home Page

NAM 12 km (31-day rotating archive)...

FTP Data

NOAA ARL FTP Server

Readme file

Grid domain map

WRF ARW (Weather Research & Forecasting Model for CAPTEX Tracer Experiment)

FTP Data

NOAA ARL FTP Server

Readme file

CAPTEX grid domain map (every 5th point shown)

North American Regional Reanalysis (NARR, 1979-2014)

FTP Data

NOAA ARL FTP Server

Readme file

NARR grid domain map(Every 5th grid point shown)

MM5 (MM5 Community Model for the METREX Tracer Experiment)

FTP Data

NOAA ARL FTP Server

Readme file

Grid domain map

CFSR (The Climate Forecast System Reanalysis)

FTP Data

NOAA ARL FTP Server

Readme file

Grid domain map (every 10th point shown)

Data No Longer Updated

FNL archive (1997-2006) of NCEP Global Data Assimilation System (GDAS) model output

***** FNL datasets are no longer online; use Reanalysis data as an alternate source of data.

Readme file

NGM (Jan. 1991 - Apr. 1997)

Readme file

Missing data listing

Latitude/longitude pairs

Grid domain map

NAM(Eta) Data Assimilation System (EDAS 80km, 1997-2004)

Readme file

Changes

2004 missing data listing

2003 missing data listing

2002 missing data listing

2001 missing data listing

2000 missing data listing

1999 missing data listing

1998 missing data listing

1997 missing data listing

Air Resources Laboratory - Gridded Data Archives https://ready.arl.noaa.gov/archives.php

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Modified: January 30, 2015

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Latitude/longitude pairs

Grid domain map

EDAS Presentation by Eric Rogers of NOAA NCEP

NCEP NAM(Eta)/EDAS and the GCIP Project

All of theses datasets contain basic fields such as the u- and v-wind components, temperature, and humidity. However, the archives differ from each other because of the horizontal

and vertical resolution, as well as in the specific fields provided by NCEP. All fields were selected by ARL according to what is most relevant for transport and dispersion studies and

disk space limitations.

Data Packing Format

NCEP typically saves their model output in GRIB format. However, at ARL the data are reprocessed and stored in a 1-byte packing algorithm. This 1-byte packing is a bit more

compact than GRIB and can be directly used on a variety of computing platforms with direct access I/O.

The data array is packed and stored into one byte characters. To preserve as much data precision as possible the difference between the values at grid points is saved and packed

rather than the actual values. The grid is then reconstructed by adding the differences between grid values starting with the first value, which is stored in unpacked ASCII form in the

header record. To illustrate the process, assume that a grid of real data, R, of dimensions i,j is given by the below example.

 1,j 2,j .... i-1,j i,j

 1,j-1 2,j-1 .... i-1,j-1 i,j-1

 .... .... .... .... ....

 1,2 2,2 .... i-1,2 i,2

 1,1 2,1 .... i-1,1 i,1

The packed value, P, is then given by

 Pi,j = (Ri,j - Ri-1,j)* (2**(7-N)),

where the scaling exponent

 N = ln dRmax / ln 2 .

The value of dRmax is the maximum difference between any two adjacent grid points for the entire array. It is computed from the differences along each i index holding j constant. The

difference at index (1,j) is computed from index (1,j-1), and at 1,1 the difference is always zero. The packed values are one byte unsigned integers, where values from 0 to 126

represent -127 to -1, 127 represents zero, and values of 128 to 254 represent 1 to 127. Each record length is then equal in bytes to the number of array elements plus 50 bytes for the

header label information. The 50 byte label field precedes each packed data field and contains the following ASCII data:

Field Format Description 

Year I2 Greenwich date for which data valid

Month I2 "

Day I2 "

Hour I2 "

Forecast* I2 Hours forecast, zero for analysis

Level I2 Level from the surface up (see Table 3)

Grid I2 Grid identification (see Table 1)

Variable A4 Variable label (see Table 2)

Exponent I4 Scaling exponent needed for unpacking

Precision E14.7 Precision of unpacked data

Value 1,1 E14.7 Unpacked data value at grid point 1,1

*Forecast hour is -1 for missing data. 

The following Fortran90 program can be used to to unpack and read the first few elements of the data array for each record of an ARL packed meteorological file.

CHK_DATA.F

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