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Sensitivity of Orographic Precipitation to Changing Ambient Conditions and Terrain Geometries: An Idealized Modeling Perspective

Abstract This paper utilizes the fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) mesoscale model (MM5) in a two-dimensional (2D) configuration at 4-km horizontal grid spacing in order to better understand the relationship between orographic precipitation and the height and width of a barrier, as well as the ambient flow, uniform moist static stability, and freezing level. The focus is on how these parameters affect the orographic precipitation by changing the circulation and microphysical structures over the barrier. As the low-level flow becomes blocked for moist nondimensional mountain heights greater than 3.0, there is a rapid upstream shift in the precipitation maximum and a reduction in precipitation over the upper windward slope. For the terrain geometries used in this study (500 to 3500 m high and 25- to 50-km half-width), the maximum precipitation is a strong function of barrier slope for relatively weak upstream flow (U = 10 m s−1). For moderate ...