Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 4 5 2004 10.5194/acpd-4-5625-2004 http://www.atmos-chem-phys-discuss.net/4/5625/2004/ http://www.atmos-chem-phys-discuss.net/4/5625/2004/acpd-4-5625-2004.html http://www.atmos-chem-phys-discuss.net/4/5625/2004/acpd-4-5625-2004.pdf 5625 5653 2004-09-22 Simulating orographic rainfall with a limited-area, non-hydrostatic atmospheric model under idealized forcing A. Pathirana pathirana@hq.unu.edu S. Herath T. Yamada Environment and Sustainable Development Programme, United Nations University, Tokyo, Japan Department of Civil Engineering, Chuo University, Tokyo, Japan A modified version of an operational 3-D, non-hydrostatic, limited-area atmospheric model (MM5) was used to perform high-resolution, idealized simulations of the interaction of a infinitely long single ridge with large-scale, steady, lateral wind field. The effect of different mountain ridge dimensions, wind speeds and patterns and moisture profiles on the quantity and distribution of orographic rainfall was investigated. The simulations demonstrated a number of commonly observed mountain flow features like formation of cap clouds, foehn wall, convective break-out associated with mountain topography, interaction of downslope winds with sea breeze, and different stages of cumulus development. Changing topographical and atmospheric parameters had clear effects on amount and pattern of accumulated rainfall. Those differences are explained by the different flow patterns observed in the model output.