Tuesday, 18 August 2009: 4:30 PM
The Canyons (Sheraton Salt Lake City Hotel)
Precipitation in Alpine regions is often a result of synoptic-mesoscale interaction of weather systems with the mountain topography. Data analysis from many orographic field experiments lead to the conclusion that orographic precipitation is primarily governed by three major components: 1) moisture flux towards the mountains, 2) mesoscale orographically-induced lift regulated by the shape and steepness of the mountain, atmospheric static stability, as well as direction and speed of the low-level jet, and 3) precipitation efficiency related to small scale turbulence, wind shear instabilities, and microphysical processes. The objective of the study is to investigate the dependency of duration, location, and intensity of heavy precipitation on upstream conditions such as static stability, low-level and upper-level jets, and converging airflow related to down-valley flow. In a first step the results from the Mesoscale Alpine Programme conducted in the European Alps 1999 focusing on processes enhancing orographic precipitation are analyzed for their long-term representativeness using operational soundings and radar observations from the three operational radars in Switzerland. For heavy precipitation events we investigate the upstream environmental conditions related to strength and direction of impinging flow relative to mountain topography, atmospheric stability, and moisture flux transport by a climatologic and statistical approach over a ten-year period. These findings are then related to analyses of multi-scale interactions of environmental conditions on the location and intensity of precipitation in Taiwan using measurements during the Taiwan Mesoscale Rainfall Experiment (TiMREX).
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