Contribution of East Indian Ocean SSTA to Western North Pacific tropical cyclone activity under El Niño/La Niña conditions

Abstract

ABSTRACTThis study investigates, under El Niño/La Niña conditions, the effects of sea surface temperature anomaly (SSTA) in the East Indian Ocean (EIO) on tropical cyclone (TC) genesis over the western North Pacific (WNP), and a possible mechanism is proposed. It is found that the EIO SSTA exerts a secondary modulation to cyclogenesis relative to the El Niño‐Southern Oscillation (ENSO), and the negative correlation between the EIO SSTA and WNP TC frequency is significantly weakened by the ENSO events. Under El Niño (La Niña) conditions, no matter what phases of EIO SSTA, TC genesis generally shows similar features with low (high) frequency in the western‐central WNP (15°–25°N, 120°–150°E) and high (low) frequency in the southeastern WNP (5°–15°N, 150°–170°E). In particular, the effects of warm EIO SSTA on the WNP TC activity represent an asymmetry between El Niño and La Niña. That is, the warm EIO SSTA and El Niño share combined effects to decrease TC genesis over the western‐central WNP. By contrast, under La Niña conditions, the influence of warm EIO SSTA on TC activity over the western‐central WNP is partially drown out by La Niña. Meanwhile, weaker monsoon trough with intense anomaly of easterly jointly induced by the two factors suppresses TC genesis over the southeastern WNP.