Monday, 17 August 2009
Arches/Deer Valley (Sheraton Salt Lake City Hotel)
This study uses ten years of data from the University of Utah Tropical Rainfall Measuring Mission (TRMM) Precipitation Feature Database to examine the diurnal cycle of rainfall over the complex terrain of the southwestern United States during the North American Monsoon in July and August. A region in Arizona and New Mexico is chosen in part because there are data available from the 10-cm operational WSR-88D radars operated by the National Weather Service, but also because there are strong similarities between this region and the Sierra Madre Occidental of Mexico studied intensively during the North American Monsoon Experiment (NAME) field program in 2004. Satellite- and surface-based rainfall estimates are complimentary. Surface-based observations are used to examine specific events, while TRMM data are used to create a climatology of thunderstorm events in the region. On most days the diurnal cycle is dominated by frequent small storms, which start before noon on the highest terrain and propagate to lower elevations during the afternoon. Occasionally (but importantly) these storms merge and continue into the low deserts in the form of a large mesoscale convective system (MCS). These larger systems produce a much greater percentage of the region's rainfall than the smaller storms earlier in the day despite their frequency. Specific case studies are used to demonstrate the development and structure of these large precipitation events and the environment in which they form, as well as the impact these events can have on the region.
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