Upscale Effects of Deep Convection during the North American Monsoon

The ability of deep monsoon convection to influence the larger-scale circulation over North America is investigated for a six day long case study during the 2006 North American monsoon season.   Results from Rossby wave ray tracing and numerical simulations using the Advanced Research Weather Research and Forecasting model indicate that North American monsoon convection provides a source region for stationary Rossby waves.  Two wave trains are seen in the numerical model simulations, with behaviors that agree well with expectations from theory and ray tracing.  The shorter and faster moving wave train moves eastward from the source region in Mexico and reaches the western Atlantic within four days.  The longer and slower moving wave train travels northeastward and reaches the coastal New England region within six days.  An upstream tail of anticyclonic vorticity extends westward from the source region into the central Pacific Ocean.

The monsoon convection appears to help cut off the low-level anticyclonic flow by developing low-level southerly flow in the Gulf of Mexico and northerly flow in the eastern Pacific, as suggested in earlier global model studies.  However, the stationary Rossby wave trains further alter the location and intensity of deep convection in locations remote from the monsoon.  Implications of these results for operational forecasting and regional climate will be discussed. 


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Thursday, July 11, 2013 - 3:30pm