A Numerical Study of The Northward Propogation of Intraseasonal Disturbances in Summer Monsoon

Observational studies have shown clear evidence of northward propogation of disturbances in both South-Asian and Western-Pacific summer monsoons at intraseasonal time sscales. These northward propogating intraseasonal disturbances can produce large fluctuations in summer monsoon rainfall. Therefore, to understand the physical processes that cause these intraseasonal signals is of great importance to improve accurate prediction of summer monsoon rainfall. Previous studies have proposed several mechanisms that may play significant roles in initiating and regulating the northward propogating disturbances at intraseasonal time scales, including the land surface hydrological effects to the north, the large-scale local air-sea interaction. In this study, we will present some of our latest coupled modeling results to demonstrate the potential roles of cloud-radiation forcing and its impact on air-sea interaction in summer monsoon at intraseasonal time scales. The atmospheric model used in this study is a zonally symmetric 2D high-resolution primitive equation model with explicit cloud microphysics and an interactive cloud-radiation scheme. This atmospheric model is coupled with a simple ocean mixed layer model which can capture the major ocean dynamical and thermodynamical processes reasonably well. Numerical experiments with/without the ocean-atmosphere coupling or the cloud-radiation forcing are conducted to isolate the role of different physical processes. Details of the results and our major findings will be presented at the conference.