Is Preconditioning Effect On Strong Positive Indian Ocean Dipole by a Preceding Central Pacific El Niño Deterministic?

Abstract

AbstractThe 2018 Central Pacific (CP) El Niño preceded the 2019 strong positive Indian Ocean Dipole (pIOD). The robustness of a CP El Niño preconditioning a strong pIOD has not been investigated. Here, we show that March‐April‐May (MAM) easterly anomalies over the equatorial eastern Indian Ocean (EIO) induced by a preceding CP El Niño drive a thermocline shallowing conducive to an early equatorial EIO cooling. However, the same winds also generate off‐equatorial downwelling Rossby waves in the southern EIO, which reflect as downwelling Kelvin waves, able to weaken the initial anomalies. Furthermore, zonal winds in June‐July‐August (JJA) can either be beneficial or unfavorable for the developing pIOD. Only when the equatorial easterlies, EIO cooling, and thermocline shallowing are sufficiently amplified by JJA does a strong pIOD occur. Despite this, a multi‐century model simulation suggests that development of majority of strong pIOD events is facilitated by a preceding CP El Niño.