Different impacts of two kinds of Pacific Ocean warming on tropical cyclone frequency over the western North Pacific

The present study examines the relationship of ENSO Modoki and canonical ENSO, respectively, with the tropical cyclone (TC) frequency over the western North Pacific (WNP) for the period 1960-2008. The TC frequency is significantly positively correlated with ENSO Modoki index. The Nio-3 index has a markedly negative (positive) correlation with the TC frequency in the northern (southeastern) portion of the WNP. In response to heating source related to El Nio Modoki, a large-scale cyclonic anomaly forms over the WNP. In contrast, during the canonical El Nio years, zonally-elongated heating source and sink exhibit a meridional dipole pattern, which induces an anticyclonic anomaly in the subtropics and a cyclonic anomaly near the equatorial central Pacific. Numerical experiments under the realistic mean state and heating profiles validate that the anomalous circulation responses to heating play essential roles in different modulations of two kinds of Pacific Ocean warming on the TC frequency. Copyright 2010 by the American Geophysical Union.