Mode of Precipitation Variability Generated by Coupling of ENSO With Seasonal Cycle in the Tropical Pacific

Abstract

Tropical precipitation anomalies show very different patterns over the central-eastern equatorial Pacific between the developing and decay phases of extreme El Niño despite similar patterns of sea surface temperature (SST) anomalies. Using observational data and atmospheric simulations for 1979–2018, we identified a meridional dipole mode of tropical precipitation variability, called the Pacific precipitation dipole mode (PPDM), which is critical for seasonally varying rainfall patterns related to extreme El Niño. We examined the mechanism of PPDM using a numerical model and found that the seasonal shift of the warm SST band in the eastern equatorial Pacific, when coupled with extreme SST anomalies, causes phase reversal of the PPDM. The PPDM can be regarded as a different manifestation of the El Niño/Southern Oscillation combination mode, as revealed by the surface wind anomalies, which also explains the distinct impact of extreme El Niño events over East Asia.