The Effect of Snow Cover and Cloud type on the Surface Radiation Budget at SURFRAD Network Stations

Since 1995, a research-quality surface radiation budget observing network (SURFRAD) has been operating over the continental United States. It was originally established to support GEWEX/GCIP, satellite retrieval validation, and weather and hydrological modeling. Its uses have since expanded to support UV research, weather and climate research, and studies of the effects of aerosols on the surface radiation balance. The first four stations were located in the Mississippi drainage basin in support of GCIP. In 1998 two stations were added in Pennsylvania and Nevada. Primary measurements at SURFRAD stations are the downwelling and upwelling components of broadband solar and thermal infrared irradiance. To support research, measurements are also made of basic meteorological parameters, and spectral bands of special interest. These include air temperature, relative humidity, and wind, aerosol optical depth, UVB irradiance, and photosynthetically active radiation. Two stations now have atmospheric energy flux and soil heat flux instrumentation, making them full surface energy balance monitoring sites. Network operation involves a rigorous regimen of frequent calibration, quality assurance, data quality control, and near-real time data dissemination. Quality controlled, daily-processed data files from each station are usually available via the internet within a day of real time. The daily processing is mostly automated for efficiency and to avoid operator error.

In 1990, the Committee on Earth and the Environmental Sciences reported that the understanding of the effects of clouds in climate and hydrologic systems was the highest priority of the U. S. Global Change Research Program. In recognition of this, hemispheric sky imagers were added at SURFRAD stations in 1999. Measurements of cloud fraction and cloud opacity, in conjunction with surface radiation budget measurements and atmospheric fluxes at some sites make SURFRAD data ideal for studies of the effects of clouds on the surface radiation budget, and for validation of the surface physics formulations of weather, hydrology, and climate models. Data from SURFRAD have been used to validate surface irradiance estimates from NASA’s EOS satellites, satellite-based retrievals of surface erythemal UV radiation, the national UV index, real-time NESDIS products, and NCEP’s operational models. SURFRAD data have also been used for carbon sequestration studies, as validation for radiative transfer codes, for basic research and instruction at universities, and many other applications.

Stations of the SURFRAD network are located in diverse climate regions of the U.S. This is important because it is likely that changing climate patterns will be manifested as extraordinary changes in regional climate characteristics. With five years of high quality surface radiation budget measurements, preliminary assessments of the surface radiation climatologies at the stations are feasible. For example, it may be possible to quantitatively infer regional climatological effects that result from anomalous weather patterns, such as those brought about by El Nino and La Nina, both of which fortuitously coincided with the SURFRAD deployment. Surface radiation climatologies for each station, as well as quantitative insights derived from these analyses will be presented. Novel software that can extract cloud effect information from solar radiation measurements alone has been adapted and successfully applied to SURFRAD data. These results will be compiled over the same intervals as the climatological averages and will be used to corroborate inferences from the climatological analyses.