2.3 Convection-permitting simulations of the diurnal cycle of warm-season precipitation in the lee of the Rocky mountains

Monday, 17 August 2009: 10:45 AM
The Canyons (Sheraton Salt Lake City Hotel)
S. B. Trier, NCAR, Boulder, CO; and C. A. Davis and D. A. Ahijevych

This work examines the role of terrain-induced wind systems on the diurnal cycle of summertime convection that develops in the lee of the Rocky Mountains. The lifecycle of deep convection is simulated using a large-domain convection-permitting version of the Weather Research and Forecast Model (WRF) that is initialized using monthly averaged conditions (July 2001) representative of an active monsoon period. The model is integrated for 10 days, however during this period the lateral boundaries of the model contain only diurnal variations. This experimental design mitigates effects of transient disturbances (e.g., mobile surface fronts, midlevel shortwaves) on precipitation. Results indicate that many salient features of the midsummer precipitation pattern found in climatological studies (e.g., Carbone et al. 2002, Tuttle and Davis 2006) are reproduced using this simple framework in which terrain-induced diurnal flows under the control of a quasi stationary longwave pattern dominate. These precipitation features include the afternoon precipitation maximum over the Rocky Mountain Cordillera followed by zonally propagating nocturnal convection confined to a narrow latitudinal corridor farther east over the central Great Plains of the United States. In this presentation we discuss the role of diurnally varying flow systems (including the mountain-plains solenoid and the nocturnal low-level jet of the central U.S.) on both the overall diurnal cycle of preciptation and on the water budget within the central U.S. where the heaviest rain occurs.
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