Precipitation Mechanisms over Complex Terrain

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The three major types of precipitating cloud systems in the atmosphere are deep convection, frontal systems, and tropical cyclones. This project examines how each is affected by the presence of mountains. The research will analyze existing datasets including those of several past National Science Foundation funded field campaigns.Intellectual Merit:Heavy precipitation and flooding in regions of complex terrain can be understood and anticipated by identifying key ingredients. This research identifies such ingredients associated with each of the three principal storm types. The ingredients for deep convection will be examined and identified by comparing behavior of heavy rain-producing convection over the Himalayas, Andes, Central Mountains of Taiwan, and the Sierra Madre Occidental of Mexico. These different venues provide a variety of synoptic and orographic settings so that the important ingredients for intense rainfall and flooding will be identified through comparison of the storms in these different regions. The parental synoptic conditions range from baroclinic waves dipping equatorward over Asia, to monsoonal conditions, to equatorial waves, and diurnal forcings. The ingredients for enhancement of precipitation when fronts cross mountain ranges will be examined for the coastal mountains of British Columbia to test the hypothesis that shear and thermally-induced turbulence enhance windward side precipitation. The ingredients associated with the passage of tropical cyclones over mountains will be studied by examining Hurricane Karl (2005) and Tropical Storm Dolly (2014) as they entered and crossed the Sierra Madre Oriental of Mexico. The roles of terrain-locked gravity waves and triggering of convection over the mountains will be examined as ingredients for modifying and prolonging the precipitation in the eyewalls and rainbands of tropical cyclones. Through studying these types of enhancement of precipitation by the major atmospheric precipitation systems as they pass over mountains and identifying key ingredients, this project will contribute to a more general understanding of the effects of mountains on precipitating clouds.Broader Impacts:This work will have the broader impact of laying groundwork for improved forecasting of heavy precipitation in regions of the earth most prone to flooding and disastrous societal impacts. Further, by better understanding how mountains affect storms, future studies may better anticipate how the patterns of occurrence of natural disasters might be altered in a changing climate. In addition, this project will optimize the use of past field campaign datasets and will contribute to training women and minorities for atmospheric sciences research.