On the Interdecadal Variation of the Warm Water Volume in the Tropical Pacific Around 1999/2000

Abstract

AbstractA profound change in the variations of warm water volume (WWV) of the tropical Pacific occurred around 1999/2000, coincided with the interdecadal shift of the El Niño–Southern Oscillation (ENSO) properties to a higher frequency and smaller amplitude regime. The persistence of WWV is decreased for all calendar months since 2000, associated with a decrease in its variance and an increase in its frequency. Moreover, the WWV‐sea surface temperature relationship associated with the ENSO cycle is weakened during 2000–2019, implying that the recharge/discharge process is less efficient in driving the phase transition of an ENSO cycle and ENSO became less periodical compared with that during 1979–1999. Corresponding to the weaker precursory connection of WWV to ENSO, the geographical origin of precedent thermocline anomalies has shown a northwestward migration since 2000. This is consistent with the suppression of the equatorial air‐sea feedback and the systematical northwestward shift of the atmosphere‐ocean coupling center in the tropical Pacific. Changed annual cycle and enhanced zonal contrast of sea surface temperature in the equatorial Pacific may be connected with the interdecadal variations of the ENSO and WWV features.