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.
Highlights
The southern tropical Indian Ocean (STIO) features remarkable intraseasonal sea surface temperature (SST) variability as a result of ocean–atmosphere interaction between Sea Surface Temperature (SST) and strong atmospheric intraseasonal oscillations (ISOs) [1,2,3,4]
Over Region B, atmospheric processes interact with the thermocline ridge, and the cold water beneath the shallow mixed layer can lead to large SST anomalies
Athe local minimum in climatology exists a shallow thermocline, which is associated with windin climatology exists over a shallow thermocline, which is associated with the wind-induced upwelling minimum in climatology existsThis over a shallow thermocline, which is associated with the windinduced upwelling in the South Tropical Indian Ocean (STIO)
Summary
The southern tropical Indian Ocean (STIO) features remarkable intraseasonal sea surface temperature (SST) variability as a result of ocean–atmosphere interaction between SST and strong atmospheric intraseasonal oscillations (ISOs) [1,2,3,4]. Meehl [29] showed SST anomalies contribute to the remarkable biennial oscillation of the monsoon precipitation He further analyzed the mechanism on maintaining the coupled ocean–atmosphere interaction [30,31]. Chen et al [34] noted the local air–sea coupling is especially important during the March–May (MAM) for precipitation prediction Both empirical and modeling studies have advanced in investigating the impact of SST on atmospheric ISOs at intraseasonal timescales. These studies showed that precipitation lags SST anomalies about 5–15 days [10,19,21,25,35].
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