MJO-induced Warm Pool Eastward Extension Prior to the Onset of El Niño: An Observational study

Abstract

The Madden-Julian Oscillation (MJO) and El Niño Southern Oscillation (ENSO) are the two most important phenomena in the Tropics that affect global weather and climate on intraseasonal to interannual timescales. Although they occur on different timescales, the MJO-induced SST changes over the western Pacific have spatial scales similar to those of SST anomalies prior and/or during the onset of El Niño. To investigate the MJO-induced SST changes and their contribution to the warm pool eastward extension (WPEE) prior to the onset of El Ni˜no, we use 20 years of Tropical Rainfall Measuring Mission (TRMM) Multi-satellite Precipitation Analysis (TMPA), Cross Calibrated Multi-Platform (CCMP) surface winds, and Optimum Interpolated Sea Surface Temperature (OISST) to quantify the time and spatial scales of MJO rain and wind, and the MJO-induced WPEE. The MJO events in the western equatorial Pacific (east of 130°E, 10°S – 10°N) are identified based on the Large-scale Precipitation Tracking (LPT). The intensity of the MJO is measured by total rain volume and zonal surface winds averaged throughout its lifetime. It is found that the majority of the MJOs (65%) induce a WPEE up to 3000 km that can last beyond 15 days. The MJO events prior to the onset of El Niño are generally stronger in convection and winds, and produce significant WPEE beyond the annual cycle. Consecutive MJO events produce much larger WPEE prior to El Niño, which has been observed in every El Niño event from 1998-2019.