Upscale
Effects of Deep Convection during the North American Monsoon
David
Stensrud
Penn State
July 21st Noon in room 2155
Abstract:
The ability of deep monsoon convection to
influence the larger-scale circulation over North America is
investigated for a 6-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 4
days.
The longer and slower moving wave train travels northeastward and
reaches the coastal New England region within 6 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.