Causality Analysis of More Tropical Cyclones Affecting Guangxi in 2013
Based on NOAA OLR, NCEP/NCAR height and wind monthly reanalysis data and CMA tropical cyclone data during 1951-2013, the causes of more tropical cyclones (TCs) that affected Guangxi in 2013 are analyzed. The results show that the West Pacific subtropical high (WPSH) was exceptionally stronger than in other years and its west ridge point abnormally stretched westward and northward from June to September 2013, which is favorable for more TCs to affect Guangxi. At the same time, the condensation latent heat released by rainfall on the south side of WPSH may be in favor of the northward extension of WSPH. Besides, the Somali crossequatorial flow was stronger than normal, and joined in a southeast air flow on the southwest side of north Pacific anticyclone over South China Sea and Philippines, forming a monsoon trough, which is very conducive to the generation of more TCs in 2013. The results also show that there were much more activities and eastward (westward) propagation of lowfrequency convections over India Ocean and west Pacific Ocean, lower SST in the eastern equatorial Pacific, stronger Hadley and Walker circulations and a westward deviation of the ascending branch of Walker circulation, and all of these factors could lead to the occurrence of more TCs in 2013.