Forcing of the Asian and North American Monsoon Anticyclones by Regional Diabatic Heating

The Asian and North American monsoon anticyclones dominate the circulation of the northern hemisphere upper troposphere and lower stratosphere (UTLS) during boreal summer. Transport by the monsoons has a strong effect on the composition of the UTLS, and hence on the Earth's weather and climate. The Asian monsoon anticyclone (AMA) has long been viewed as, to first order, a linear response to the latent heat released by the tropical and subtropical precipitations; but the North American monsoon anticyclone (NAMA) has received less attention. We analyze the mechanisms responsible for the AMA and NAMA by using an idealized dry general circulation model (GCM) with specified zonally-asymmetric diabatic heat sources. The model uses simplified Held-Suarez physical parameterizations that produce realistic equinoctial and solstitial zonal-mean circulations through Newtonian relaxation and Raleigh damping. Results will focus on the individual and combined contributions of diabatic heating in the eastern and western hemispheres to the AMA and NAMA respectively. Hypotheses for the origin of the NAMA, such as downstream effects of the AMA or an independent response to latent heating in the Western Hemisphere, will be examined through numerical experiments.