On the Linkage Between the Asian Summer Monsoon and Tropopause Folds

This study uses a set of idealized aquaplanet model experiments to investigate the linkage between the Asian summer monsoon circulation and tropopause fold activity. It is found that folds tend to occur on the northwestern side of the upper-level anticyclone associated with the monsoon circulation and are generated due to intensified monsoon circulation and resulting intensified subsidence. In addition, the impact of tropopause folds on extreme rainfall events is also examined. It is found that while the likelihood of extreme rainfall is largely decreased at and upstream of the occurrence of folds, the likelihood is significantly increased downstream. This pattern of suppression of extreme rainfall upstream and promotion downstream also persists for about 1–2 days, which likely suggests a positive feedback between extreme rainfall downstream and tropopause folds. Finally, changes in tropopause folds with monsoon intensity are also discussed.