Western Pacific Oceanic Heat Content: A Better Predictor of La Niña Than of El Niño

Abstract

The western equatorial Pacific oceanic heat content (warm water volume in the west or WWVw) is the best El Niño–Southern Oscillation (ENSO) predictor beyond 1-year lead. Using observations and selected Coupled Model Intercomparison Project Phase 5 simulations, we show that a discharged WWVw in boreal fall is a better predictor of La Niña than a recharged WWVw for El Niño 13 months later, both in terms of occurrence and amplitude. These results are robust when considering the heat content across the entire equatorial Pacific (WWV) at shorter lead times, including all Coupled Model Intercomparison Project Phase 5 models or excluding Niño-Niña and Niña-Niño phase transitions. Suggested mechanisms for this asymmetry include (1) the negatively skewed WWVw distribution with stronger discharges related to stronger wind stress anomalies during El Niño and (2) the stronger positive Bjerknes feedback loop during El Niño. The possible role of stronger subseasonal wind variations during El Niño is also discussed.