Microphysics and Optics in Trade Wind Cumulus Clouds

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This study will be part of the Rain in Cumulus over the Ocean (RICO) experiment, a collaborative study of trade-wind Cumuli and of rain formation in warm clouds that will be conducted in the winter of 2004-2005. This investigator will have primary responsibility for two airborne instruments, a Particle Volume Monitor (PVM) to measure the liquid water content of clouds and a new integrating nephelometer that measures the surface area of the cloud droplet population. The RICO studies of precipitation formation and of mechanisms that broaden the cloud droplet size distribution will benefit from accurate measurement of the liquid water content, and the integrating nephelometer will provide a benchmark for other instruments that measure the cloud droplet size distribution. Because the PVM can measure the liquid water content at very high rate (up to 1000 Hz), its measurements will provide an important opportunity to identify the degree to which cloud parcels are diluted by entrainment of environmental air, a process that has an important effect on rain formation. This and other studies in RICO are expected to lead to a better understanding of how rain forms in clouds that do not reach the freezing level and a better characterization of precipitation and other processes that occur in shallow trade-wind clouds. Because such clouds cover large areas of the Earth and are now poorly understood, this study in association with others in RICO has the potential to lead to better representations of precipitation and radiative transfer in climate models.