Biological and Environmental Research - Earth and Environmental System Sciences
Earth and Environmental System Modeling
15 June 2020

ENSO Regime Changes Responsible for Decadal Phase Relationship Variations Between ENSO Sea Surface Temperature and Warm Water Volume

Science

ENSO events can be predicted up to three seasons in advance due to the slow equatorial heat content recharge/discharge in the upper ocean. The warm water volume (WWV), describing upper Pacific Ocean heat content, usually leads the ENSO SST evolution by a quarter of the ENSO period and acts as a useful predictor for ENSO SST. However, this WWV-ENSO SST phase-lag relationship has experienced a significant shift around 2000 with the lead time being shortened from approximately two to three to approximately one season. Here we attribute the decadal change of the WWV-ENSO SST phase-lag relation to decadal ENSO regime shifts.

Impact

We show that the ocean memory associated with heat content recharge-discharge still co-occurs with the ENSO evolution during these decades and that WWV still acts as an ENSO precursor but with significantly reduced lead time. The WWV-ENSO SSTA relationship is crucially dependent on ENSO regimes associated with EP and CP types. However, current dynamical and statistical ENSO forecast models have difficulties in simulating two distinct ENSO types, thus potentially explaining decreases in forecast skill in decades that were characterized by frequent occurrences of CP ENSO events.

Summary

The relationship between WWV and Niño3.4 SST varies on decadal timescales, corresponding to the occurrence frequency of central Pacific ENSO. Both eastern and central Pacific ENSO events show recharge/discharge signatures but with different WWV/Niño3.4 phase-lag relationships. This difference can be explained by the existence of two different ENSO types characterized by distinct intrinsic periodicities. 

Contact
Fei-Fei Jin
University of Hawaii - Manoa
Publications
Zhang, W, S Li, F Jin, R Xie, C Liu, M Stuecker, and A Xue.  2019.  "ENSO Regime Changes Responsible for Decadal Phase Relationship Variations Between ENSO Sea Surface Temperature and Warm Water Volume."  Geophysical Research Letters 46(13): 7546-7553.  https://doi.org/10.1029/2019gl082943.