Transport and Stirring by the Asian Monsoon Anticyclone

During boreal summer the Asian monsoon anticyclone (AMA) dominates the atmospheric circulation of the northern hemisphere upper troposphere and lower stratosphere (UTLS). The convection that drives the AMA also transports water and pollutants from the lower troposphere to the UTLS. This air can be exported from within the AMA to the global tropical upper troposphere and the northern hemisphere lower stratosphere by large-scale stirring. Here we analyze the mechanisms responsible for stirring air into and out of the AMA by using air parcel trajectories computed with wind fields that have been filtered to remove selected space and time scales. We focus on the role of Rossby waves propagating along the subtropical jet on the northern flank of the AMA, and on the importance of fluctuations in the size and strength of the AMA circulation itself due to variations in convective heating.