Understanding Lead Times of Warm Water Volumes to ENSO Sea Surface Temperature Anomalies.

The equatorial Pacific warm water volume (WWV) and western equatorial Pacific WWV (WWVw) are two important long‐lead time El Niño‐Southern Oscillation (ENSO) event precursors. Here, we utilize the recharge‐discharge oscillator framework to obtain the analytical solution of WWV and WWVw lead times to ENSO sea surface temperatures (SSTs). Both WWV and WWVw lead times show a strong dependence on the inherent ENSO periodicity, whereas WWV lead time is further modulated by the air‐sea coupling strength and ENSO SST spatial pattern. The derived solution is able to explain observed decadal variations in lead times of WWV to SST in terms of variations in ENSO periodicity and air‐sea coupling strength. Plain Language Summary: Predicting El Niño‐Southern Oscillation (ENSO) events in advance has profound socio‐economic benefits because of ENSO's impacts on global weather and climate. The basin‐wide equatorial Pacific heat content (also known as warm water volume, WWV) and western Pacific WWV (WWVw) are well‐known predictors of ENSO events several seasons ahead. In this study, we present an analytical expression of WWV and WWVw lead times to ENSO sea surface temperature (SST) anomalies. The analytical solution can explain the observed decadal changes in WWV lead times. We demonstrate that the recent shortened WWV lead time observed after the year 2000 can be largely explained by a decrease in the inherent ENSO periodicity, and second by an increase in the air‐sea coupling strength. The latter is associated with an ENSO SST spatial pattern change with more frequent occurrences of Central Pacific El Niño events in recent decades. Key Points: Theoretical lead times of basin‐wide warm water volume (WWV) and western Pacific WWV (WWVw) to El Niño‐Southern Oscillation (ENSO) events are validatedWWV lead time depends on both ENSO periodicity and the ENSO spatial pattern, whereas WWVw lead time depends solely on ENSO periodicityObserved decadal variations of WWV lead times result from variations in ENSO periodicity and air‐sea coupling strength [ABSTRACT FROM AUTHOR]