9.3 A VOCALS perspective on precipitation closure

Thursday, 1 July 2010: 8:30 AM
Cascade Ballroom (DoubleTree by Hilton Portland)
Paquita Zuidema, Univ. of Miami/RSMAS, Miami, FL; and D. Leon and J. R. Snider

Precipitation is known to increase with liquid water path (LWP) and decrease with cloud droplet number concentration (Nd) as a result of the collision-coalescence process. The exact sensitivity is less well-known. Rainrate sensitivities to LWPaNd-b  report values for "a" and "b" that range between 1.5-2.0 and 0.6-1.75 respectively, with more uncertainty in the role played by the cloud droplet number than by cloud liquid water amount. Intuitively, one would expect microphysical process rates that are independent of location, with improved instrumentation and methodologies ultimately providing consensus. One objective for VOCALS is to provide additional observational closure on precipitation sensitivities, capable of serving as a robust model metric. A unique aspect of the VOCALS-REx was the inclusion of three cloud remote sensors on the NCAR C-130: the Wyoming Cloud Radar and Lidar and an 183 GHz millimeter radiometer, providing complementary observations on the cloud boundaries, the cloud liquid water path, and on the precipitation vertical structure. In combination with in situ measurements on the cloud microphysical and aerosol environment at flight altitude, a rainrate parameterization can be constructed that is based on a relatively large, well-sampled dataset. This will be shown and discussed, along with sensitivities to, e.g., mesoscale cellular structure, averaging scale, and vertical velocity. These, in addition, may help explain differences between similar surface- and space-based assessments.
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