Sea Surface Temperature (SST) Variability in the Indian Ocean

Among the tropical oceans, the Indian Ocean is the smallest and the warmest. The tropical Indian Ocean forms the major part of the largest warm pool (SST > 28 °C) among the global oceans. Tropical Indian Ocean SST plays a significant role in shaping climate as well as its variability on both regional (Chowdary et al. 2015) and global scales (Schott et al. 2009), and it is hence important to know the characteristics of Indian Ocean SST on spatial and temporal scales. Indian Ocean exhibits climate variability in several timescales, ranging from diurnal to interannual, and is strongly coupled to the seasonal cycle (Schott et al. 2009). The Indian Ocean also exhibits long-term trends in temperatures at both the surface (Roxy et al. 2014) and the subsurface (Lee et al. 2015), with an impact on the local monsoon Hadley circulation (Roxy et al. 2015), interannual variability (Chakravorty et al. 2014a) and the intraseasonal variability (Sabeerali et al. 2014).

The tropical ocean-atmosphere system exhibits marked variability in the intraseasonal timescales (Lau and Waliser 2012). Central to the intraseasonal variability is the Madden-Julian Oscillation (MJO), which was first discovered as an atmospheric phenomenon (Madden and Julian 1971, 1972, 1994) over the equatorial oceans. Subsequent experiments like the MONEX (see Murakami 1979) and BOBMEX revealed strong intraseasonal signals in the Bay of Bengal as well (Krishnamurti et al. 1988; Bhat et al. 2001). This intraseasonal variability in SST is closely associated with the atmospheric variability at similar scales (10-20 days and 30-90 days) and acts as a coupled phenomenon (Sengupta et al. 2001; Vecchi and Harrison 2002; Roxy and Tanimoto 2007; Vialard et al. 2012; Roxy et al.

2012). On the other hand, the intraseasonal SST variability in the Arabian Sea is forced by the oceanic processes (Vialard et al. 2012). A recent field campaign called the Dynamics of MJO/Cooperative Indian Ocean Experiment on Intraseasonal Variability in Year 2011 (DYNAMO/CINDY2011) traces the initiation of the MJO events to local ocean atmospheric processes over the Indian Ocean (Li et al. 2015). Several model studies addressed the intraseasonal SST variability associated with MJO and the associated processes (e.g. Jayakumar et al. 2011).

On interannual and decadal timescales, the Indian Ocean SSTs are influenced by two prominent modes of variability, namely El Nino Southern Oscillation (Rasmusson and Carpenter 1982; ENSO) and the Indian Ocean Dipole (IOD; Saji et al. 1999; Webster et al. 1999; Murtugudde et al. 2000).

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