LDAS

Data for LDAS

An experimental multi-parameter data base, as produced in support of GCIP, is provided here for 1998, for the entire United States. It was prepared to meet the needs of the Land Data Assimilation Scheme (LDAS) Project, which is a joint collaboration of the following organizations: NCEP; NASA Goddard; Princeton University; Office of Hydrology; University of Washington; Rutgers University; and the University of Maryland. Details about this project can be found at: The LDAS Hompage

Under LDAS, research efforts are in progress to prevent errors in forcing from accumulating in the surface energy balance terms of Numerical Weather Prediction (NWP) models, that lead to incorrect partitioning of the energy balance terms. The methodology adopted by the LDAS group is to force the models with observations and thus prevent the NWP forcing biases. The LDAS is forced with real time output from numerical prediction models, satellite data, and radar precipitation measurements.

The parameters provided here were requested by the LDAS implementation group. They are a subset of 71 parameters that are being produced by NOAA/NESDIS and the University of Maryland, in support of GCIP activities. The following categories of parameters are provided: Top of the Atmosphere radiative fluxes; Surface radiative fluxes; Optical depths; Satellite Radiances; and ancillary data. In addition to the already available parameters, the following are provided in the Historic Data Archive:

surface upward SW flux (42)
surface downward diffuse SW flux (46)
surface downward diffuse PAR (47)
TOA clear-sky upward SW flux (43)
aerosol optical depth (28)
cloud optical depth (29)
surface temperature (9)
channel 4 radiance (15)
channel 5 radiance (16)
number of clear pixels (20)
number of cloudy pixels (21)
column precipitable water (22)
target mean albedo in channel 1 (2)
target mean temperature in channel 2 (in K) (4)
Target mean temperature in channel 4 (in K) (8)
Target mean temperature in channel 5 (in K) (10)
Target standard deviation in channel 1 (52)
Target standard deviation in channel 4 (55)
Target standard deviation in channel 1 albedo (32)

NOTE: Cloud amount is calculated as:
(number of cloudy pixels )/(number of cloudy pixels + number of clear pixels)

The numbers in parentheses indicate the location of the parameter in the original list of 71 parameters, as produced in real time by NOAA/NESDIS. The parameters listed above are available in the Historic Data Archive.

Results of evaluation of the satellite estimates of surface insolation against observations at four SURFRAD sites, for four months in 1998, are presented for:

• May 1998
• August 1998
• October 1998
• December 1998

The results for December illustrate known problems of cloud screening over snow. For all other snow free cases, results are similar to the examples given here.

Future plans: After a period of evaluation, this additional information will be provided retroactively from the beginning of the GCIP experiment (also to be placed in "Historic Data") and in real time (to be placed in "Current Data").