On the Linkage between Asian Summer Monsoon and Tropopause Folds

Tropopause folds are important dynamical processes of troposphere-stratosphere coupling and are characterized by deformation of the tropopause and intrusion of stratospheric air into the troposphere. Previous studies on tropopause folds mostly focused on the extratropical folds and much less on the summer folds. Recent studies examined the global climatology of tropopause folds using observations, found a “hot spot” of summertime fold activity over the eastern Mediterranean and the Middle East and suggested a linkage with the Asian summer monsoon. 

In this study, we aim to better understand the linkage between the Asian summer monsoon and tropopause folds using a set of idealized aquaplanet model experiments with prescribed sea surface temperatures (SSTs). A monsoon-like large-scale atmospheric circulation is induced when a zonally-asymmetric SST anomaly is added in the Northern Hemisphere subtropics. We find that tropopause folds are well simulated in aquaplanet model experiments and their location and frequency are similar to that in observations. In addition, during the occurrence of tropopause folds, increase of precipitation is always seen downstream. We will discuss about the underlying mechanism and possible implications with a changing monsoon strength.