Impacts of freshwater flux anomaly on the development of El Niño/Southern Oscillation

– Takahito Kataoka, JAMSTEC –

Résumé :

During El Niño, positive sea surface temperature (SST) anomalies in the central-eastern tropical Pacific are accompanied by positive precipitation anomalies. In this study, we investigate the roles of freshwater flux anomaly in the development of El Niño/Southern Oscillation (ENSO) using a state-of-the-art climate model. In addition to the control experiment (CTRL), where the atmosphere and ocean are fully coupled everywhere, two sensitivity experiments are conducted: the freshwater flux associated with either precipitation or evaporation over the tropical Pacific Ocean is replaced with the 3-hourly climatology from CTRL. It is found that precipitation anomaly significantly enhances ENSO variability by up to about 20%, while evaporation anomaly does not. Positive precipitation anomaly during El Niño shoals the mixed layer, which thickens the barrier layer and thus, reduces the vertical temperature gradient. In addition, vertical mixing is weakened due to stabilization. These reduce the cooling by the vertical mixing, resulting in warmer SSTs. In addition, I would like to briefly highlight my work on seasonal-to-decadal climate predictions and mechanism studies for other tropical climate variability, if time allows.