Influence of Indian Ocean Dipole on Tropical Cyclone Activity over Western North Pacific in Boreal Autumn

Abstract

In this study, we investigated the influence of the Indian Ocean Dipole (IOD) on the interannual variability of tropical cyclone (TC) activity over the western North Pacific (WNP) during autumn (September–November) from 1961–2015. We found the number of TCs making landfall in China to be significantly negatively correlated with the IOD index, which can be attributed to shifts in the location of TC formation together with the abnormal steering flow at 500 hPa. During negative IOD autumns, TC genesis regions move obviously westward due to the westward retreat of the WNP monsoon trough. The TC activity is remarkably enhanced near South China coastal areas, which is due to a contiguous 500-hPa subtropical ridge. In contrast, during positive IOD autumns, TC genesis positions obviously shift eastward and more TCs tend to exhibit recurvature around 130°E or a westward path south of 15°N led by an equatorward movement of the 500-hPa subtropical ridge with a break near 125°E. In our examination of large-scale circulation, we found a pair of equator-symmetric anticyclones in the lower troposphere resulting from variations in the large-scale Walker circulation induced by the anomalous sea surface temperature (SST) associated with a positive IOD. The resulting Philippines anti-cyclonic anomalies are closely related to the variability of the monsoon trough over the WNP region. Furthermore, the variations in the steering flow can be explained by the suppressed (enhanced) convective activities around the Philippines and the weakened (strengthened) local meridional circulation over East Asia in positive (negative) IOD years.