Breaks in the Asian Monsoon: The Influence of Southern Hemisphere Weather Systems

Abstract

Atmospheric model results suggest that chaotic weather systems in the Southern Hemisphere midlatitudes can trigger ?breaks? in the Indian monsoon rainfall. Indeed, the mechanism may be able to trigger a more general break of the entire Asian monsoon. The mechanism proposed involves the injection of dry, high negative potential vorticity air from the Southern Hemisphere midlatitudes into the low-level monsoon inflow. Observations from the 1994 monsoon season tend to support this mechanism and, if true, it may imply some predictive skill for shorter-range forecasting. However, the mechanism proposed may also imply that an accurate seasonal forecast of monsoon rainfall is an impossible objective, with important consequences for the agricultural economies of the region. Results are presented from both an idealized model and a full general circulation model.