Department of Atmospheric Sciences, University of Illinois Urbana-Champaign
October 3, 2007
3:00 pm: Conversation and Cookies in Room 109 ASB
3:30 pm: Seminar in Room 144 Loomis Lab
Despite steady advances in understanding the internal workings of supercell thunderstorms, as well as the external environmental conditions favorable for their development, the key elements differentiating tornadic from non-tornadic supercell storms remain elusive. Recent observation-based research suggests only subtle differences in rear flank downdraft (RFD) thermodynamic character may be all that delineates tornadic behavior, though unfortunately direct observations of cold pool characteristics are rarely available for warning operations. Further, the dominant physical and dynamic processes which modulate RFD characteristics are attributed to a broad spectrum of mechanisms within the literature. In this work, a method is developed to take advantage of dual polarization radar which provides volumetric data on time scales reasonable for capturing some aspects of microphysical evolution. An ensemble Kalman filter based assimilation system coupled with a two-moment microphysical scheme enables ingestion of polarimetric observations and subsequent retrieval of detailed physical state estimates of storms and the near storm environment. This offers a new window into severe storms by fusing polarimetric radar observations, detailed microphysics and storm kinematics. Subsequently, aspects such as a severe storm’s rear flank downdraft kinematic and thermodynamic evolution can be assessed to evaluate the sensitivity of a storm’s cold pool characteristics to microphysical evolution. Spatial and temporal evolution of key polarimetric field variables will be presented for a violent tornadic supercell storm that swept through the Oklahoma City metropolitan area on 8 May 2003, along with preliminary results to reconstruct the evolution of these features via the developed polarimetric assimilation system. Implications from this work toward enhancing predictability of severe storm hazards from polarimetric assimilation systems will also be addressed.
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