This data set contains the secondary forcing data "File B" for Phase 2 of the North American Land Data Assimilation System (NLDAS-2).  The data are in 1/8th degree grid spacing and range from Jan 1979 to the present. The temporal resolution is hourly.  The file format is WMO GRIB-1.

Details about the generation of the NLDAS-2 forcing datasets can be found in Xia et al. (2012).

The non-precipitation land surface forcing fields for NLDAS-2 are derived from the analysis fields of the NCEP North American Regional Reanalysis (NARR). NARR analysis fields are 32-km spatial resolution and 3-hourly temporal frequency.  Those NARR fields that are utilized to generate NLDAS-2 forcing fields are spatially interpolated to the finer resolution of the NLDAS 1/8th-degree grid and then temporally disaggregated to the NLDAS hourly frequency.  NLDAS-2 is providing a second forcing file, "File B", in which the surface temperature,
humidity, and wind fields are represented not at 2-meters and 10-meters above the height of the NLDAS terrain, but rather at the same height above the NLDAS terrain as the height above the NARR terrain of the lowest prognostic level of the NARR assimilation system (namely, the same height above the model terrain as the lowest prognostic level of the mesoscale Eta model, which is the assimilating model in NARR).

The surface downward surface radiation field in "File B" is taken directly from NARR, without any bias correction.  The precipitation and convective precipitation fields in "File B" are also taken directly from NARR, and are used to calculate the convective fraction provided in "File A".  The aerodynamic conductance is "File B" is also taken from NARR.

The hourly land surface forcing fields for NLDAS-2 are grouped into two GRIB files, "File A" and "File B".  "File B" is the secondary (optional) forcing file and contains ten fields.  The data set applies a user-defined parameter table to indicate the contents and parameter number.  The GRIBTAB file (http://disc.sci.gsfc.nasa.gov/hydrology/grib_tabs /gribtab_NLDAS_FORB_hourly.002.txt) shows a list of parameters for this data set, along with their Product Definition Section (PDS) IDs and units.

For more information, please see the README Document at ftp://hydro1.sci.gsfc.nasa.gov/data/s4pa/NLDAS/README.NLDAS2.pdf.