Application of A Global-To-Beam Irradiance Model to the Satellite-Based NASA GEWEX SRB Data and Validation of the Results against the Ground-Based BSRN Data

The NASA/GEWEX SRB (Surface Radiation Budget) project has produced a 24.5-year continuous global record of shortwave and longwave radiation flux dataset at TOA and the Earth's surface from satellite measurements. The time span of the data is from July 1983 to December 2007, and the spatial resolution is 1 degree latitude by 1 degree longitude. SRB products are available on 3-hourly, 3-hourly-monthly, daily and monthly time scales. The inputs to the models include: 1.) Cloud parameters derived from pixel-level DX product of the International Satellite Cloud Climatology Project (ISCCP); 2.) Temperature and moisture profiles of the atmosphere generated with the Goddard Earth Observing System model Version 4.0.3 (GEOS-4.0.3) from a 4-D data assimilation product of the Data Assimilation Office at NASA Goddard Space Flight Center; 3.) Atmospheric column ozone record constructed from the Total Ozone Mapping Spectrometer (TOMS) aboard Nimbus-7 (July 1983 - November 1994), from the Operational Vertical Sounder aboard the Television Infrared Observation Satellite (TIROS, TOVS) (December 1994 - October 1995), from Ozone Monitoring Instrument (OMI), and from Stratospheric Monitoring Ozone Blended Analysis (SMOBA) products; 4.) Surface albedos based on monthly climatological clear-sky albedos at the top of the atmosphere (TOA) which in turn were derived from the NASA Clouds and the Earth's Radiant Energy System (CERES) data during 2000-2005; 5.) Surface emissivities from a map developed at NASA Langley Research Center. The SRB global irradiances have been extensively validated against the ground-based BSRN (Baseline Surface Radiation Network), GEBA (Global Energy Balance Archive), and WRDC (World Radiation Data Centre) data, and generally good agreement is achieved. In this paper, we apply the DirIndex model, a modified version of the DirInt model, to the SRB 3-hourly global irradiances and derive the 3-hourly beam, or direct normal, irradiances. Daily and monthly mean direct normal and diffuse irradiances are derived. The input variables include, among others, surface pressure, precipitable water, geopotential height of the surface, 10-meter temperature, and specific humidity from GEOS, and AOD at 700 nm derived from the MATCH (Model for Atmospheric Transport and CHemistry) data. The DirIndex model is modified to accommodate the ranges of the input variables wider than specified in the original DirIndex model. The results are then validated against their BSRN counterparts. Compared with an earlier empirical model for monthly means, the results from the modified DirIndex model shows appreciable improvement.