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Description
This data set contains the primary forcing hourly data "File A" 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 netCDF (converted from the GRIB data files).
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. Additionally, the fields of surface pressure, surface downward longwave radiation, near-surface air temperature, and near-surface specific humidity are adjusted vertically to account for the vertical difference between the NARR and NLDAS fields of terrain height. This vertical adjustment applies the traditional vertical lapse rate of 6.5 K/km for air temperature. The details of the spatial interpolation, temporal disaggregation, and vertical adjustment are presented by Cosgrove et al. (2003).
The surface downward shortwave radiation field in "File A" is a bias-corrected field wherein a bias-correction algorithm was applied to the NARR surface downward shortwave radiation. This bias correction utilizes five years (1996-2000) of the hourly 1/8th-degree GOES-based surface downward shortwave radiation fields derived by Pinker et al. (2003). The potential evaporation field in "File A" is that computed in NARR using the modified Penman scheme of Mahrt and Ek (1984).
The precipitation field in "File A" is not the NARR precipitation forcing, but is rather a product of a temporal disaggregation of a gauge-only CPC analysis of daily precipitation, performed directly on the NLDAS grid and including an orographic adjustment based on the widely-applied PRISM climatology. The precipitation is temporally disaggregated into hourly fields by deriving hourly disaggregation weights from either WSR-88D Doppler radar-based precipitation estimates, 8-km CMORPH hourly precipitation analyses, or NARR-simulated precipitation (based on availability, in order). The latter fields from radar, CMORPH, and NARR are used only to derive disaggregation weights and do not change the daily total precipitation. The field in "File A" that gives the fraction of total precipitation that is convective is an estimate derived from the following two NARR precipitation fields (which are provided in "File B"): NARR total precipitation and NARR convective precipitation (the latter is less than or equal to the NARR total precipitation and can be zero). The Convective Available Potential Energy (CAPE) is the final variable in the forcing data set, also interpolated from NARR.
The hourly land surface forcing fields for NLDAS-2 are grouped into two files, "File A" and "File B". "File A" is the primary (default) forcing file and contains eleven meteorological forcing fields. Details about the generation of the NLDAS-2.0 forcing datasets can be found in Xia et al. (2012).
Product Summary
Platforms
Forcing-LSM
Instruments
NOT APPLICABLE
Spatial Extent
N: 53S: 25E: -67W: -125
Spatial Resolution
0.125 Decimal Degrees x 0.125 Decimal Degrees
Location
NORTH AMERICA
Coordinate System
CARTESIAN
Granule Spatial Representation
CARTESIAN
Temporal Extent
1979-01-01 to Present
Data Partner
Goddard Earth Sciences Data and Information Services Center (formerly Goddard DAAC), Terrestrial Information Systems Laboratory, Earth Sciences Division, Science and Exploration Directorate, Goddard Space Flight Center, NASA (NASA/GSFC/SED/ESD/TISL/GESDI
Citation is critically important for dataset documentation and discovery. This dataset is openly shared, without restriction, in accordance with the EOSDIS Data Use and Citation Guidance.
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Citation Copied
NLDAS Project. (2020). NLDAS Primary Forcing Data L4 Hourly 0.125 x 0.125 degree V2.0 [Data set]. NASA Goddard Earth Sciences Data and Information Services Center. https://doi.org/10.5067/THUF4J1RLSYG Date Accessed: 2026-05-26
NLDAS Project. “NLDAS Primary Forcing Data L4 Hourly 0.125 x 0.125 Degree V2.0.” NASA Goddard Earth Sciences Data and Information Services Center, 2020. doi:10.5067/THUF4J1RLSYG. Date Accessed: 2026-05-26
NLDAS Project. NLDAS Primary Forcing Data L4 Hourly 0.125 x 0.125 Degree V2.0. NASA Goddard Earth Sciences Data and Information Services Center, 2020, doi:10.5067/THUF4J1RLSYG. Date Accessed: 2026-05-26
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