Cloud and Dynamical Processes of Precipitating Warm Cumuli During RICO

The WKA will carry an array of cloud, atmospheric state, wind, radiation, and flux probes, in addition to the WCR. The WCR is a 95 GHz Doppler radar, providing high-resolution reflectivity and velocity data in vertical and horizontal sections along the flight track. The ability to place airborne in situ observations in the context of radar- derived echo and vertical velocity information at ~30 m resolution constitutes a powerful tool for cloud and precipitation studies. The PIs have extensive experience in using this combination of observing systems. The proposed work will explore the linkages between the kinematic evolution of warm marine cumulus and precipitation development, as well as between the cloud microphysical and the dynamical processes that sustain precipitating cumulus clusters. The objectives are twofold, but interconnected. The first objective is to use the WCR transects, together with the in situ thermodynamic and cloud data, and situational data from S-POL, to diagnose features of the cloud structure that bear most importantly on the initial formation of precipitation. Substantial evidence exists that the development of precipitation in warm cumulus is strongly influenced by processes of scales smaller than that of the cumulus or even its updraft, making the high- resolution radar and in situ data we plan to gather specially appropriate for this objective. The second objective relates to the mesoscale dynamics of precipitating warm cumuli. What processes control cell regeneration in cumulus clusters, whose lifetime far exceeds that of the cells? How do evaporative cooling and entrainment contribute to the formation of a cold pool, and how does that cold pool interact with ambient shear? Or is the primary mechanism by which cold pools organize tropical convection primarily thermo- dynamic, driven by convectively-induced surface fluxes? The dynamical interpretation will be based on multi-scale observations: the temporal and mainly horizontal S-POL perspective, plus ambient soundings, set a context for the WCR-based description of the fine-scale vertical cloud and kinematic structure of cumulus clusters, and WCR data in turn are a context for the WKA-measured variations in the thermodynamic, kinematic and water fields. The objectives of this proposal are fully consistent with overall RICO goals. The flight plans proposed have been incorporated into those presented in the Facility Request for the WKA. Those flight plans have been devised to make efficient use of flight hours for our objectives and for those of collaborators. The broader impacts of the proposed work include the further development of methods of cloud studies with instrumented aircraft and aircraft-mounted cloud radar and the collection of millimeter radar data in preparation for NASA's launching of a similar radar (CloudSat). Shallow, precipitating cumuli are ubiquitous over tropical oceans, yet models of the global atmospheric circulation (GCMs), which are used for climate prediction, generally assume that these clouds do not precipitate. A better understanding of the microphysical to mesoscale processes governing these clouds will yield a more accurate parameterization of their effects in GCMs and in numerical weather prediction models. The research will also advance understanding of fundamental cloud physics, aerosol/cloud interaction and precipitation measurement issues. The proposed research will also support the training of graduate students in the special techniques of these studies, and will engender collaboration among a wide range of scientists. 1 This proposal is written as a joint effort between the University of Wyoming and NOAA ARL. The NOAA ARL budget will be covered under a proposal submitted to NOAA's Office of Global Programs under the NOAA Climate and Global Change Program. The two proposals are identical and their objectives represent a close synergy between the two groups.