The 30-50-day intraseasonal oscillation of sst and precipitation in the South Tropical Indian Ocean

Abstract

The Sea Surface Temperature (SST) in the South Tropical Indian Ocean (STIO) displays significant intraseasonal oscillation (ISO) in two regions. A striking 30-50-day ISO found over the east of thermocline ridge (Region A, 80-90° E, 6-12° S), as identified by the Empirical Mode Decomposition (EMD) method, is distinguished from the SST signature over the thermocline ridge (Region B, 52.5-65° E, 6-13° S). The 30-50-day ISO of SST in the Region A is active in March-May (MAM) and suppressed in September-November (SON). Meanwhile, a 30-50-day ISO of precipitation correlates with the SST over the Region A. SST leads precipitation by 10 days, implying a pronounced ocean-atmosphere interaction at the intraseasonal timescale, especially the oceanic feedback to the atmosphere during Madden-Julian Oscillation (MJO) events. Analysis on mechanism of the ISO manifests heat fluxes are critical to the development of the intraseasonal SST variability. The local thermocline in Region A, as the shallowest in MAM and the thickest in SON, is likely to modulate the strength of ISO and contribute to its sustainability. It suggests that thermocline plays a more important role in Region A than in Region B, leading to the difference between the two regions.