This paper analyzes the evolution of the South Asian High (SAH) during and after the development of tropical cyclone Neoguri over the South China Sea (SCS) in mid-April 2008, the formation of tropical storm Nargis over the Bay of Bengal (BOB) in late April, and the Asian summer monsoon onset, as well as their interrelationships. Numerical sensitivity experiments are conducted to explore the underlying mechanism responsible for these seasonal transitions in 2008. It is demonstrated that strong latent heating related with tropical cyclone activities over the SCS can enhance the development of the SAH aloft and generate zonal asymmetric potential vorticity (PV) forcing, with positive vorticity advection to its east and negative advection to its west. Following the decay of the tropical cyclone, this asymmetric forcing leads to instability development of the SAH, presenting as a slowly westward-propagating Rossby wave accompanied by a westward shift of the high PV advection. A strong upper tropospheric divergence on the southwest of the SAH also shifts westward, while positive PV eddies are shed from the high PV advection and eventually arrives in the southern BOB. Such synoptic patterns provide favorable pumping conditions for local cyclonic vorticity to develop. The latent heating release from the cyclogenesis further intensifies the upper-layer divergence, and the lower and upper circulations become phase locked, leading to the explosive development of the tropical cyclone over the southern BOB. Consequently, a tropical storm is generated and the BOB summer monsoon commences.
[Wu, Guoxiong; Ren, Suling; Bao, Qing; Liu, Boqi; Liu, Yimin] Chinese Acad Sci, Inst Atmospher Phys, State Key Lab Atmospher Sci & Geophys Fluid Dynam, Beijing 100029, Peoples R China; [Ren, Suling; Xu, Jianmin] China Meteorol Adm, Natl Satellite Meteorol Ctr, Beijing 100081, Peoples R China; [Ren, Suling] Chinese Acad Sci, Grad Univ, Beijing 100049, Peoples R China; [Wang, Dongxiao] Chinese Acad Sci, South China Sea Inst Oceanol, State Key Lab Trop Oceanog, Guangzhou 510301, Guangdong, Peoples R China; [Liu, Boqi] Nanjing Univ Informat Sci & Technol, Key Lab Meteorol Disaster, Minist Educ KLME, Nanjing 210044, Jiangsu, Peoples R China.Impact of tropical cyclone development on the instability of South Asian High and the summer monsoon onset over Bay of Bengal,CLIMATE DYNAMICS,2013,41(41892):2603-2616
