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Keywords:

  • moisture source;
  • interannual variability;
  • southern Indian Ocean;
  • sea surface temperature;
  • ENSO

Abstract

In boreal summer, the southern Indian Ocean (SIO) features more evaporation than precipitation and thus it is a moisture source region for the Asian summer monsoon rainfall. In the present study, the interannual variability of moisture source over the SIO is analysed for boreal summer during 1979-2008. The impacts of local sea surface temperature (SST) and the El Niño-Southern Oscillation (ENSO) on the moisture source are compared and the possible mechanisms for the SST influence on the moisture source are investigated. The leading mode of the interannual variation of apparent moisture sink (<Q2>) over the SIO displays an obvious out-of-phase relationship over the western-central SIO and the region to the northwest-north of Australia. The interannual variations of < Q2> over the above two regions have significant positive correlation with local SST. An increase in local SST enhances convection and ascent, leading to more precipitation. Over the western-central SIO, surface winds weaken corresponding to higher SST in the western-central SIO and lower SST to the northwest-north of Australia, leading to less oceanic evaporation. Thus, the variation of the moisture source over the western-central SIO is contributed by both precipitation and evaporation. However, the variation of the moisture source to the northwest-north of Australia is contributed mainly by precipitation. ENSO amplifies anomalous moisture source induced by local SST anomalies. ENSO and local SST work cooperatively to influence the moisture source over the SIO. Copyright © 2012 Royal Meteorological Society