’n‹…˜f¯‰ÈŠwêU@’n‹…‰ÈŠwçt‡•”“Á•Êu‰‰‰ï “úŽž: •½¬‚Q‚T”N‚P‚OŒŽ‚P‚W“úi‹àj‚P‚OF‚O‚O@`@‚P‚QF‚O‚O êŠF‹ž“s‘åŠw —ŠwŒ¤‹†‰È‚P†ŠÙ‚TŠK‚T‚U‚R†Žº u‰‰‘è–¼F What controls the inter annual variability of tropical cyclone activity over the western North Pacific? u‰‰ŽÒF Professor Dr. Yuqing Wang (International Pacific Research Center/Department of Meteorology School of Ocean and Earth Science and Technology University of Hawaii at Manoa, USA) u‰‰—vŽ|F In this talk, factors and physical mechanisms that dominantly controlthe inter annual variability of tropical cyclone (TC) genesis frequency over the western North Pacific (WNP) in the last three decades (since 1981) will be discussed. The modulation of the WNP TC genesis frequency by two major factors, namely the sea surface temperature anomaly (SSTA) over the eastern Indian Ocean and the anomaly in SST gradient (SSTG) between the Southwest Pacific and the western Pacific warm pool, will be shown based on both reanalysis data and regional climate model experiments. The results show that the interannual variability of the WNP TC genesis frequency is largely controlled by the two factors since 1981 through their significant impacts on the summer circulation over the major TC genesis region over the WNP. The relationship between the WNP TC genesis frequency and the two factors shows a large decadal variation with an interdecadal shift in the later 1970fs. This interdecadal shift is shown to be mainly controlled by two effects: the continuous warming with an area-expansion of the Indian Ocean and the change of SSTA patterns over the central and eastern equatorial Pacific. The involved mechanisms are investigated using both regional and global atmospheric models. –â‚¢‡‚킹æF —¢‘º—Y•F