Experimental and Numerical Investigations of Spectral Broadening and the Onset of Precipitation in Warm Rain In Cumulus over the Ocean (RICO) Cumuli

Stratton Park Engineering Co., Inc., Boulder CO

Investigators

Abstract

The "Rain in Cumulus over the Oceans" experiment will be a multi-investigator study of warm rain formation and the nature of trade wind Cumulus clouds. One hypothesis being investigated in that experiment is that turbulent air motions in clouds increase the collision rates among cloud droplets and so accelerate the formation of rain. These investigators will participate in that study by contributing measurements of the spatial inhomogeneities in droplet locations in the clouds. Using those measurements, they will evaluate the possibility that such inhomogeneities lead to faster rain formation than would be present without turbulence. Unique instruments will include a new "2D-S" (Two-Dimensional Stereo) imaging probe, an updated version of a cloud particle imager that can provide information on the spatial distribution of hydrometeors with fine resolution, and an instrument that measures the location of each droplet encountered with high resolution. These instruments promise to provide reliable measurements of quantities previously difficult to measure from aircraft, including the drizzle size range and the clustering of droplets. If they are shown to be reliable, they have the potential to contribute to many future studies of microphysical processes in clouds. The 2D-S probe in particular could make a major contribution to research objectives of all RICO investigators if it provides good documentation of the 30-200 micrometer droplet size range because this is of crucial importance to the project objectives and is poorly measured by standard instruments. The instrumentation development and testing that will occur as part of this project may benefit future measurement programs as well. Analysis efforts in subsequent years will include collaboration with modelers to represent microphysical processes in clouds in ways that are consistent with the observed characteristics.