An interdecadal change in the interannual variability of boreal summer tropical cyclone genesis frequency over the western North Pacific around the early 1990s

Abstract

This study presents an interdecadal change in the interannual variability of the tropical cyclone (TC) genesis frequency (TCGF) over the western North Pacific (WNP) around the early 1990s, which is characterized by decreasing in the periodicity and standard deviation of the total TC number (TCN) and shifting in genesis location of the TC over the WNP. This interdecadal change is largely associated with the changes in the impacts of the individual and combined modes of the sea surface temperature anomalies (SSTAs) in tropical Indo-Pacific Ocean (TIPO). Results indicate that prior to the early 1990s, the interannual variability of the WNP TCGF is closely influenced by the La Niña-like SSTAs in the tropical Pacific Ocean (TPO), which leads to a zonally dipole structure in the WNP TCGF by triggering an anomalous anticyclone over the southeastern WNP and an anomalous cyclone over the northwestern WNP. Since the early 1990s, the interannual variability of the WNP TCGF is attributed to the impacts of the Indian Ocean Basin mode (IOBM) SSTAs in the tropical Indian Ocean (TIO) and the El Niño Modoki-like SSTAs in the TPO, which may work individually and jointly by inducing an anomalous cyclone over the WNP through a Rossby wave-type and a Kelvin wave-type response, respectively. In addition, the IOBM SSTAs in the TIO play a leading role in the impacts on the interannual variability of the WNP TCGF during the recent period. These results also indicate an interdecadal change in the relationship between the TCGF over the WNP and the Indo-Pacific SSTAs, which may provide a good implication for seasonal prediction of the TC activity over the WNP.