Shift in MONSOON–SST teleconnections in the tropical Indian Ocean and ENSEMBLES climate models' fidelity in its simulation

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Abstract

ABSTRACT The climate shift in 1976–1977 sets a clear distinction in the teleconnection between Indian summer monsoon rainfall ( ISMR ) and sea surface temperatures ( SST ) in the tropical oceans, particularly in the tropical Indian Ocean ( TIO ). Before the climate shift (Pre‐77), the observed correlation between ISMR and SST was positive in the eastern equatorial Indian Ocean ( EIO ) and negative correlation prevailed in the western equatorial Indian Ocean ( WIO ), whereas after the climate shift (Post‐77), the correlation pattern has reversed (i.e. positive correlation in WIO and negative correlation in EIO ). The major reason for this shift is the consistent warming of SSTs throughout the tropics and frequent occurrence of IOD events. Further, it is noticed that during the earlier decades, the Indian Ocean was responding to the atmospheric forcing, particularly along the axis of strong cross equatorial flow, whereas in the recent decades, Indian Ocean dynamics are playing a crucial role in determining the SST in major parts of the Indian Ocean particularly in the EIO . Seasonal re‐forecasts from six state‐of‐the‐art global coupled atmosphere–ocean climate models which participated in ENSEMBLES faithfully capture the pre‐77 dipole structure of correlations. But the post‐77 correlation pattern is not simulated by any of the six models considered in this study. Two possible reasons are pointed out for the models' inability to capture the reversal of teleconnection: (1) in the coupled models, unchanged mean state of the winds inhibits ISMR to be governed by coupled dynamics in the TIO ; (2) the strong, local SST –rainfall relationship in models even in post‐77 period limits the influence of the teleconnections on the ISMR .

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