THE SPECTRAL RADIANCE EXPERIMENT (SPECTER) - PROJECT DESCRIPTION AND SAMPLE RESULTS

The fundamental climatic role of radiative processes has spurred the d evelopment of increasingly sophisticated models of radiative transfer in the earth-atmosphere system. Since the basic physics of radiative t ransfer is rather well known, this was thought to be an exercise in re finement. Therefore, it came as a great surprise when large difference s (30-70 W m(-2)) were found among longwave infrared fluxes predicted by over 30 radiation models for identical atmospheres during the inter comparison of radiation codes used in climate models (ICRCCM) exercise in the mid-1980s. No amount of further calculation could explain thes e and other intermodel differences; thus, it became clear that what wa s needed was a set of accurate atmospheric spectral radiation data mea sured simultaneously with the important radiative properties of the at mosphere like temperature and humidity. To obtain this dataset, the IC RCCM participants charged the authors to develop an experimental field program. So, the authors developed a program concept for the Spectral Radiance Experiment (SPECTRE), organized a team of scientists with ex pertise in atmospheric field spectroscopy, remote sensing, and radiati ve transfer, and secured funding from the Department of Energy and the National Aeronautics and Space Administration. The goal of SPECTRE wa s to establish a reference standard against which to compare models an d also to drastically reduce the uncertainties in humidity, aerosol, e tc., which radiation modelers had invoked in the past to excuse disagr eements with observations. To avoid the high cost and sampling problem s associated with aircraft, SPECTRE was designed to be a surface-based program. The field portion of SPECTRE took place 13 November to 7 Dec ember 1991, in Coffeyville, Kansas, in conjunction with the FIRE Cirru s II field program, and most of the data have been calibrated to a usa ble form and will soon appear on a CD-ROM. This paper provides an over view of the data obtained; it also outlines the plans to use this data to further advance the ICRCCM goal of testing the verisimilitude of r adiation parameterizations used in climate models.