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  • Annamalai, H., K. Hamilton, and K. R. Sperber, South Asian summer monsoon and its relationship with ENSO in the IPCC AR4 simulations. J. Climate. Submitted.

The ability of global coupled models to capture the ENSO-monsoon association is examined in the climate of the 20th century (20c3m) integrations submitted to the IPCC Fourth Assessment Report (AR4). For a proper representation of ENSO-monsoon relationship, we propose that a realistic simulation of the time-mean monsoon precipitation and evolution of sea surface temperature and diabatic heating anomalies in the equatorial Pacific during ENSO are essential.

Of the 18 models examined here, only six are found to have realistic representation of monsoon precipitation climatology in the 20c3m integrations, and in the 2xC02 runs, all of them predict an increase (in the range 5-25%) in monsoon precipitation over the Indian sub-continent, as well as an increase in its variability (5-10%).

For each of these six models correlation statistics between all-India rainfall (AIR) index and SST over the tropical Indo-Pacific regions for each realization are calculated and then an ensemble mean pattern is computed. Only four models exhibit a robust ENSO-monsoon teleconnection pattern similar to observations, a feature that remains intact and stronger under the climate change scenario. As regards to the timing of the teleconnection, three models represent the observed spring predictability barrier, namely the transition from positive to negative correlations prior to the monsoon onset. Furthermore, only one of these three model captures the observed phase lag with the strongest anticorrelation of SST peaking 2-3 months after the summer monsoon. In the 20c3m and the 2xCO2 runs (1pctto2x) (1) the overall range and time scales of variation of the monsoon-ENSO relationship remain similar, and (2) there is little consistency in the phase among the individual realizations. Item (1) indicates that there is no evidence for a weakening in the ENSO-monsoon connection due to global warming, and item (2) suggests a lack of predictability of the decadal modulation of the monsoon-ENSO relationship. Further examination reveals that models that capture the ENSO-monsoon teleconnection have fidelity in correctly simulating the timing and location of SST and diabatic heating anomalies during El Nino events, lending credence to our hypothesis. The implication of these results on the monsoon prediction are discussed.

Last Updated: 2006-02-27

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