Interdecadal variability of tropical cyclone genesis frequency in western North Pacific and South Pacific ocean basins

Abstract

Variability of tropical cyclone (TC) genesis frequency in the western North Pacific and South Pacific ocean basins in the interdecadal scale is studied. It is demonstrated that the TC genesis frequency in these ocean basins experienced an abrupt decrease near the end of the 20th century. The decreased occurrence of TC genesis in the two recent decades is mainly located in the low-latitude regions at the eastern side of the two ocean basins. It is also shown that a significant part of the decreased TC genesis occurred during October to December, i.e. the post-peak season in the western North Pacific ocean basin and the pre-peak season in the South Pacific ocean basin. The interdecadal trend of variation in the TC genesis frequency in these adjacent two ocean basins seems to be mainly due to a common mechanism, i.e. the variation in the atmospheric vorticity. In contrast to the decrease in the total TC genesis, the intense typhoon occurrence frequency experienced an interdecadal increase during the same period. This trend for intense typhoons is particularly clear in the western North Pacific ocean basin. The zonal distribution of the increased number in the intense typhoon occurrence shows a similar pattern to the increased value of the sea surface temperature. It is then suggested that the variation in the intense typhoon occurrence frequency in the western North Pacific ocean basin is related to a change in the La Niña-like sea surface warming pattern.