GODAS: Global Ocean Data Analysis System

GODAS

The NCEP Global Ocean Data Assimilation System (GODAS) uses

       continuous real-time data from the Global Ocean Observing System. 
       This project is to deliver routine ocean monitoring products, 
       and is being implemented by the Climate Prediction Center in 
       cooperation with NOAA's Office of Climate Observation (OCO).

Data Availability

GRIB-1: Monthly and pentad data can be downloaded by clicking on the Binary Data link at the GODAS website.

netCDF: GODAS data can be downloaded from the NOAA/OAR/ESRL Physical Sciences Division (PSD), Boulder, Colorado, USA, from their Web site at http://www.cdc.noaa.gov/data/gridded/data.godas.html. The data adhere to the COARDS netCDF convention. The data files contain one variable for each year.

One peculiarity with the PSD GODAS files is that they include missing_value and _FillValue attributes that are different (Click here for an example.). NCL only recognizes _FillValue. Hence, the user must make some changes. See Example 4.

NCL Comments

The golden rule of 'data processing' is to look at the data prior to processing. The command line utility, ncl_filedump, can be used to examine a file's contents. It readily accepts files in a variety of formats including GRIB and netCDF. Sample results from use on a GODAS GRIB file and a NOAA/OAR/ESRL/PSD netCDF file:

        ncl_filedump -itime godas.M.200901.grb

        ncl_filedump thflx.2008.nc

The output from ncl_filedump on the GRIB can be seen here and on the netCDF file can be seen here. The GRIB file has all the variables for a particular year-month while the netCDF has one variable for each month of the year.

NCL can import the data directly. NCL does not care which format is input:

1. NCL will unpack the GRIB directly.
2. The netCDF files provided by NOAA/OAR/ESRL/PSD contain variables of type "short". The NCL function short2flt can be used to unpack the values and retain all meta data.

NCL's coordinate subscripting is used in several of the examples. This allows the use of 'physical coordinates' to access subsets of the data. This is more convenient then using subscript indices.