Relationship between Pacific Ocean warming and tropical cyclone activity over the western North Pacific

摘要

El Nino has distinctive oceanic and atmospheric signatures that have different influences on tropical cyclone (TC) activity over the western North Pacific (WNP). This study compares TC activity over the WNP basin among strong Central-Pacific (CP), mixed CP, and strong Eastern-Pacific (EP) El Nino. Results suggest that TC activity with strong intensity and long lifespan occurred more frequently during strong (i.e. strong EP and strong CP) El Nino years than during mixed-CP El Nino years. This is attributed primarily to a combined modulation of the amplitude and duration of warm sea-surface temperature anomalies (SSTAs) over the tropical Pacific, and variations in large-scale environmental conditions; i.e. eddy kinetic energy, omega, relative humidity, and vertical wind shear (VWS). During CP (i.e. strong CP and mixed CP) El Nino events, enhanced TC genesis is observed over a large part of the WNP. During strong-CP El Nino events, more TCs are generated east of 140 degrees E in the southwestern WNP, whereas more TCs are generated west of 140 degrees E during mixed-CP El Nino events. This is due to a reduced magnitude of VWS and a westward shift in warm SSTAs over the central equatorial Pacific. When an anomalous anticyclonic circulation over the Indo-China Peninsula is combined with a westward extension of the western North Pacific subtropical high, TCs heading northward are associated with strong mean winds during strong El Nino events, resulting primarily from enhanced eddy kinetic energy, omega, and relative humidity, and weak VWS. Overall, TC activity during the three types of El Nino shows distinct generation locations, evolution patterns, and intensities, and the evolving spatial patterns of SSTA play an important role in modulating TC activity.