Validation of the IPCC AR4 Monthly Mean Surface Downward Shortwave and Longwave Radiative Fluxes against the BSRN Data

The Intergovernmental Panel on Climate Change (IPCC) has played a significant role in evaluation and assessment of the global climate system. In addition to observed data, IPCC has also used model data for the purpose. An important part of the model data is the shortwave and longwave radiative fluxes at TOA and the Earth's surface. The quality of these data sets directly influence the reliability of IPCC's assessment of the climate. The NASA Global Energy and Water Cycle Experiment (GEWEX) Radiative Flux Assessment (RFA) project aims to produce reliable radiation datasets through intercomparisons of different datasets as well as comparisons with the ground-based measurements. The Baseline Surface Radiation Network (BSRN) has so far produced about 4800 site-months of surface radiation data from 43 surface stations over the time span from 1992 up to the present, and these datasets have been considered the best-quality available ground-based measurements. The BSRN radiation data are made at 1-, 2-, 3-, or 5-minute intervals and practically make a continuous record of the radiative processes. Sophisticated quality-control procedure is first applied to filter out any data points suspected to be bad. Then proper algorithm and criteria are designed to process the data to produce 3-hourly, daily and monthly means. In this presentation, we focus on the IPCC AR4 surface downward shortwave and longwave monthly mean fluxes from January 1992 to December 1999 and compare them with their BSRN counterparts. The time span is based on the coincidental temporal coverage of the IPCC AR4 data and the BSRN data. The comparisons found that for the shortwave surface downward monthly mean fluxes on the basis of 642 site-months, the bias and RMS for the "average" version are -16.38 and 25.25 watts per square meter, respectively, and for the "median" version are 0.30 and 19.46 watts per square meter, respectively; for the longwave surface downward monthly mean fluxes on the basis of 1397 site-months, the bias and RMS for the "average" version are -41.49 and 44.46 watts per square meter, respectively, and -9.49 and 17.07 watts per square meter, respectively.