THE ATMOSPHERIC RADIATION - MEASUREMENT (ARM) PROGRAM - PROGRAMMATIC BACKGROUND AND DESIGN OF THE CLOUD AND RADIATION TEST-BED

The Atmospheric Radiation Measurement (ARM) Program, supported by the U.S. Department of Energy, is a major new program of atmospheric measu rement and modeling. The program is intended to improve the understand ing of processes that affect atmospheric radiation and the description of these processes in climate models. An accurate description of atmo spheric radiation and its interaction with clouds and cloud processes is necessary to improve the performance of and confidence in models us ed to study and predict climate change. The ARM Program will employ fi ve (this paper was prepared prior to a decision to limit the number of primary measurement sites to three) highly instrumented primary measu rement sites for up to 10 years at land and ocean locations, from the Tropics to the Arctic, and will conduct observations for shorter perio ds at additional sites and in specialized campaigns. Quantities to be measured at these sites include longwave and shortwave radiation, the spatial and temporal distribution of clouds, water vapor, temperature, and other radiation-influencing quantities. There will be further obs ervations of meteorological variables that influence these quantities, including wind velocity, precipitation rate, surface moisture, temper ature, and fluxes of sensible and latent heat. These data will be used for the prospective testing of models of varying complexity, ranging from detailed process models to the highly parameterized description o f these processes for use in general circulation models of the earth's atmosphere. This article reviews the scientific background of the ARM Program, describes the design of the program, and presents its status and plans.