The NLDAS downward shortwave radiation forcing data is derived from two sources; the NCEP Eta Data Assimilation System (EDAS) and NOAA GOES satellites. The Eta Data Assimilation System provides 3-hourly time averaged downward shortwave radiation. GOES data is processed by the University of Maryland Surface Radiation Budget Group to produce hourly instantaneous downward shortwave radiation data valid at 15 minutes past the hour (Version 1 data at 0.5 degree resolution product was used, Version 2.1 at 0.125 degree will be used in the near future). Both data sets are spatially interpolated to the NLDAS 1/8th degree grid and temporally interpolated to be valid on the hour using a zenith angle based interpolation algorithm which acts to maintain a proper solar diurnal cycle. Whenever it is available, the GOES product is then overlayed on top of the EDAS data. Since, the UMD GOES product is not valid at low zenith angles and there is a discontinuity between the GOES data and the EDAS data near the day and night terminators. An example of this overlay procedure is shown in the following figure:

Example of radiation product overlay in the NLDAS 1/8th degree forcing.
UMD/GOES-RED(2), EDAS-GREEN(1), NIGHT-BLUE(0), WHITE-UNDEFINED(-999.9)

To provide more complete information on the composition of the NLDAS radiation forcing files we have produced hourly binary files containing the spatial distribution of the products used over the NLDAS grid. During Mosaic LSM execution, at each 15 minute model timestep, two of these instantaneous NLDAS radiation files were weighted to produce the data required by the model. Thus, only if GOES data was missing for two consecutive hours did the LSM go completely without any GOES SW data.

FTP ACCESS : Hourly binary SW Radiation Composition Files (gzipped and placed in monthly tar files)

Binary files were written on a little endian Linux PC
Key: 1.0 = EDAS; 2.0 = GOES; 0.0 = NIGHT; -999.0 = UNDEFINED
Here is a sample GrADS control file : radcomposition.ctl
Here is a snippet of FORTRAN code that could be used to read in the data:

real radout(464,224)
open(unit=10,file='1996100100.radsource.bin',status='old',form='unformatted')
read(10) radout
close(10)

We have also produced a listing of the daytime hours in which GOES data was unavailable over the entire NLDAS 1/8th degree grid. At the daytime hours, only EDAS data was used to produce the NLDAS SW fields.

For Hourly Listing of EDAS only NLDAS Forcing Times CLICK HERE (Format: YYYYMMDDHH)

LDAS Web Page  Developed and Maintained at NASA/GSFC

Brian A. Cosgrove: Brian.Cosgrove@gsfc.nasa.gov   Charles J. Alonge: Charles.Alonge@gsfc.nasa.gov