Global Land Data Assimilation System Version 2 (hereafter, GLDAS-2) has two components: one forced entirely with the Princeton meteorological forcing data (hereafter, GLDAS-2.0), and the other forced with a combination of model and observation based forcing data sets (hereafter, GLDAS-2.1).  

This data set, GLDAS-2.0 0.25 degree monthly generated through temporal averaging of the 3-hourly data, contains a series of land surface parameters simulated from the Noah Model 3.3, currently covers from 1948 to 2010 and will be extended to recent years as the data set becomes available.

The model simulation was initialized on simulation date January 1, 1948, using soil moisture and other state fields from the LSM climatology for that day of the year. The simulation was forced by the global meteorological forcing data set from Princeton University (Sheffield et al., 2006). The simulation used the common GLDAS data sets for land cover (MCD12Q1: Friedl et al., 2010), land water mask (MOD44W: Carroll et al., 2009), soil texture (Reynolds, 1999), and elevation (GTOPO30).  The MODIS based land surface parameters are used in the current GLDAS-2.x products while the AVHRR base parameters were used in GLDAS-1 and previous GLDAS-2 products (prior to October 2012).

The main objective for Version 2 is to create more climatologically consistent data sets using the Princeton forcing data sets extending from 1948. In Version 1, forcing sources switched several times throughout the record from 1979 to present, which introduced unnatural trends and exhibited highly uncertain forcing fields in 1995-1997. Other enhancements made in Version 2 include model version upgrade, switching to MODIS based land surface parameter data sets, and initialization of soil moisture over desert.  In NOAH model, the bottom layer temperature data set was also updated.  More details regarding the land surface parameter data changes at http://ldas.gsfc.nasa.gov/gldas/. 

WGRIB or other GRIB reader is required to read the files. The data set applies a user-defined parameter table to indicate the contents and parameter numbers. The GRIBTAB file (http://disc.sci.gsfc.nasa.gov/hydrology/grib_tabs/gribtab_GLDAS_V2.txt) shows a list of parameters for this data set, along with their Product Definition Section (PDS) IDs and units.

There are four vertical levels for the Soil Moisture (PDS 086) and Soil Temperature (PDS 085) in the Noah GRIB files. For more information, please see the README Document at http://hydro1.sci.gsfc.nasa.gov/data/s4pa/GLDAS/GLDAS_NOAH025_3H.020/doc/README.GLDAS2.pdf or the GrADS ctl file at ftp://hydro1.sci.gsfc.nasa.gov/data/gds/GLDAS/GLDAS_NOAH025_M.020.ctl.