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PRECIPITATION MEASUREMENT MISSIONS

Precipitation Microphysics

Raindrop Shapes

TRMM’s Precipitation Radar (PR) is the first space-borne radar to observe rain droplet characteristics as they travel through the atmosphere. These measurements yield invaluable information on the intensity and distribution of the rain, the type of rain, the height of the storm and the altitude at which falling snow melts into rain. Estimates of the heat released into the atmosphere at different heights based on these measurements will improve models of global atmospheric circulation.

Diagram of raindrop sizes
Equilibrium drop shapes for
drop diameters of 1-6mm.

GPM’s Dual-frequency Precipitation Radar (DPR) adds a second frequency to its radar instrument, which provides more accurate precipitation information and improves our ability to look at raindrop characteristics including structure, intensity and convective processes throughout the atmospheric column. Information on the distribution and size of precipitation particles, together with microwave radiometer information, improves the accuracy of rain and snowfall estimates. DPR measurements will offer insights into the microphysical processes of precipitation, including evaporation, collision/coalescence and aggregation among others, and will help to distinguish between regions of rain, snow and sleet. It will also provide bulk precipitation properties such as intensity, water fluxes and columnar water content. GPM’s advanced instruments will significantly improve our ability to detect light rain and falling snow and will help us investigate potential links between rainfall and human impacts on the environment such as pollution and urban environments.