Analyses of Kwajalein Experiment (KWAJEX) and Southern African Regional Science Initiative (SAFARI-2000) Data

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This award supports analysis of data collected by the Cloud and Aerosol Research Group (CARG) of the University of Washington, using its Convair-580 research aircraft, in two field projects: the Kwajalein Experiment (KWAJEX) in the Marshall Islands in 1999, and the Southern African Regional Science Initiative (SAFARI 2000) in Southern Africa in the late summer of 2000. In these experiments, the airplane was equipped for measuring cloud microphysical characteristics, the concentrations of trace gases, and the sizes, shapes, composition, and optical properties of aerosol particles. KWAJEX was focused primarily on investigating cloud and precipitation processes in tropical convective clouds. Studies under way include (1) investigating the unexpected observation that drops appear to shatter at relatively warm temperatures (warmer than -10C) and produce large numbers of ice splinters as a source of secondary ice nuclei; (2) analyzing the evidence for very rapid rain production by the collision and coalescence of liquid cloud droplets; (3) investigating the origin and properties of the extremely narrow cloud filaments (tens of meters across) in which the rain initially forms. The SAFARI observations were designed to document the chemical and physical properties of the pall of polluted air over the Atlantic Ocean off the coast of Southern Africa. The data are well suited for evaluating the effects of the smoke from biomass burning on atmospheric chemistry and on the transfer of solar and terrestrial radiation. A goal is to determine the climatic impact of the smoke through both its direct effect on the atmospheric radiative balance and its indirect effect, caused by changes in the microstructure and hence the optical characteristics of clouds that ingest the smoke. Special attention is being given to the unique data from SAFARI on atmospheric trace gases. The rates of emission for many species were measured, and will be used as inputs for chemical transport models for comparison with the downwind aircraft measurements. A goal is to understand the evolution of anthropogenic emissions (aerosols and gases), including their interaction with clouds, well enough to predict their effect on the radiative balance.