Impacts of SST anomalies in the Indian-Pacific basin on Northwest Pacific tropical cyclone activities during three super El Niño years

Abstract

This study investigated the impact of sea surface temperature (SST) in several important areas of the Indian-Pacific basin on tropical cyclone (TC) activity over the western North Pacific (WNP) during the developing years of three super El Nino events (1982, 1997, and 2015) based on observations and numerical simulations. During the super El Nino years, TC intensity was enhanced considerably, TC days increased, TC tracks mostly recurved along the coasts, and fewer TCs made landfall in China. These characteristics are similar to the strong ENSO-TC relationship but further above the climatological means than in strong El Nino years. It indicates that super El Nino events play a dominant role in the intensities and tracks of WNP TCs. However, there were clear differences in both numbers and positions of TC genesis among the different super El Nino years. These features could be attributed to the collective impact of SST anomalies (SSTAs) in the tropical central-eastern Pacific and East Indian Ocean (EIO) and the SST gradient (SSTG) between the southwestern Pacific and the western Pacific warm pool. During 2015, the EIO SSTA was extremely warm and the anomalous anticyclone in the western WNP was enhanced, resulting in fewer TCs than normal. In 1982, the EIO SSTA and spring SSTG showed negative anomalies, followed by an increased anomalous cyclone in the western WNP and equatorial vertical wind shear. This intensified the conversion of eddy kinetic energy from large-scale flows, favorable for the westward shift of TC genesis. Consequently, anomalous TC activities during the super El Nino years resulted mainly from combined SSTA impacts of different key areas over the Indian-Pacific basin.