The Impact Of Indian Ocean Basin Warming And Enso On Tropical Cyclone Activities Over The Western North Pacific

Base on the tropical cyclone (TC) data from Joint Typhoon Warning Center, the monthly mean reanalysis Sea Surface Temperature (SST) data from Hadley Centre Sea Ice and SST data set (HadlSST), monthly mean reanalysis data of wind and geopotential height fields from National Centers for Environmental Prediction and National Center for Atmospheric Research (NCEP/NCAR), precipitation data from Global Precipitation Climatology Project (GPCP), monthly mean reanalysis data of Outgoing Longwave Radiation(OLR) from National Oceanic and Atmospheric Administration (NOAA), and ECHAM4general circulation model. The relations between warming of Indian ocean basin and TC in Western North Pacific (WNP) from1950-2010were investigated and compared with the relations between ENSO and TC in WNP by meteorological statistical methods that such as Season-reliant Empirical Orthogonal Function (S-EOF), etc. The main conclusions are as follows:The abnormal warming of Indian ocean basin is well related with the frequency of weak TC in WNP. The warming of Indian ocean basin happens with the abnormal anticyclone in WNP which suppresses convection and lead to decrease of rainfall and TC. Meanwhile, the frequency of landing weak TC in HaiNan, Eastern China decreased and vise versa. In addition, Both the abnormal cold or abnormal warm of Indian ocean basin, the frequency of weak TCs formation increases remarkably in the western quadrant(0°～30°N,105°E～140°E),and decreases in the eastern quadrant (0°～30°N,140°E～180°E),but the frequency of weak TCs formation in the Southwest quadrant is most in the western quadrant.Different from the impact of Indian Ocean on weak TC, ENSO mainly cause the frequency of strong TC in WNP. In developing year of El Nino, monsoon tough goes deeply and moves eastward which cause the TC born eastward. As the TC has a long live over the ocean, the frequency of intense TC increase. On the occurrence frequency, more intense TCs land Taiwan and Southern Japan. In developing year of La Nina, the monsoon tough is low cause TC born westward lead to decrease of frequency of intense TC. Few intense TCs land Taiwan and Southern Japan. It is also found that the relationship between ENSO and the frequency of intense TCs has a decadal variation. Correlation coefficient of ENSO index and intense TC frequency is0.575and0.725during1950-1969and1990-2009, while it is only0.021during1970-1989.The numerical experiment results show that:during July to September, The abnormal warming of Indian ocean basin, which lead to increase of rainfall, and the maximum value of precipitation positive anomalies were mainly located in the eastern equatorial Indian Ocean, An closed zonal circulation circle stretch across the North Indian Ocean and WNP, with abnormal subsidence locates near the Philippine islands, which suppresses convection and reduce precipitation,which is helpful to develop and maintain the anomalous anticyclone of WNP, consistent with its result of data analysis.