Studies of Orographic Precipitation Processes

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The fundamental scientific problem to be addressed in this research is to use polarization radar signatures to understand the microphysical evolution of mountain cloud systems, and improve methodologies for interpreting polarization radar signatures in a wide variety of cloud systems. The specific objectives are to use polarization radar measurements from the Mesoscale Alpine Programme (MAP) and the Improvement of Microphysical Parameterization through Observational Verification Experiment (IMPROVE II) in conjunction with aircraft microphysical data to address two key unresolved scientific questions: 1) How does topography affect microphysical processes and precipitation development within cloud systems as they approach and ascend major topographic barriers and finer scale topographic features? 2) What is the role of warm rain microphysics on precipitation processes in mountain cloud systems? Fundamental to achieving these scientific objectives is the quantitative interpretation of particle types from polarization measurements in orographic cloud systems. The intellectual merit of the research has its basis in the new understanding it will provide concerning the role of mountains in enhancing precipitation. The research also will explore novel ways to interpret measurements from polarization radars. While past studies of orographic cloud systems have been restricted to targets of opportunity when aircraft data or vertically pointing remote sensors were available, this study will take advantage of four dimensional polarization radar coverage, allowing examination in much finer detail of the relationship of microphysical processes to evolving cloud structures both upstream and over the mountain ranges. The results will also have application to non orographic systems where the transitions in microphysical processes with distance are not as abrupt. The broader impacts of the proposed research are significant. The proposed research has direct relevance to the effective management of water resources in mountainous regions, since polarization radars will be used in the future in the United States and internationally, to measure precipitation. The research will contribute directly toward understanding precipitation processes over the European Alps and the Oregon Cascades. In both these regions, water resources are closely tied to orographic precipitation. Forecast model developers will use the results of this research to evaluate precipitation parameterizations and improve the prediction of precipitation in mountainous regions. This is important since accurate prediction of precipitation can reduce the economic impacts of frequent heavy precipitation events that often produce catastrophic floods. The research will also lead to a better interpretation of polarization radar data, which will be important both in the United States and in other countries as polarization radars become operational and products become available to forecasters and the public.