Interannual variability in the barrier layer and forcing mechanism in the eastern equatorial Indian Ocean and Bay of Ben
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Interannual variability in the barrier layer and forcing mechanism in the eastern equatorial Indian Ocean and Bay of Bengal Tian Ma1, Xuhua Cheng1, 2, 3*, Yiquan Qi1, Jiajia Chen1 1 Key Laboratory of Marine Hazards Forecasting, Ministry of Natural Resources, Hohai University, Nanjing 210098,
China 2 College of Oceanography, Hohai University, Nanjing 210098, China 3 Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai 519000, China
Received 31 October 2019; accepted 28 November 2019 © Chinese Society for Oceanography and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract
Interannual variability (IAV) in the barrier layer thickness (BLT) and forcing mechanisms in the eastern equatorial Indian Ocean (EEIO) and Bay of Bengal (BoB) are examined using monthly Argo data sets during 2002–2017. The BLT during November–January (NDJ) in the EEIO shows strong IAV, which is associated with the Indian Ocean dipole mode (IOD), with the IOD leading the BLT by two months. During the negative IOD phase, the westerly wind anomalies driving the downwelling Kelvin waves increase the isothermal layer depth (ILD). Moreover, the variability in the mixed layer depth (MLD) is complex. Affected by the Wyrtki jet, the MLD presents negative anomalies west of 85°E and strong positive anomalies between 85°E and 93°E. Therefore, the BLT shows positive anomalies except between 86°E and 92°E in the EEIO. Additionally, the IAV in the BLT during December– February (DJF) in the BoB is also investigated. In the eastern and northeastern BoB, the IAV in the BLT is remotely forced by equatorial zonal wind stress anomalies associated with the El Niño-Southern Oscillation (ENSO). In the western BoB, the regional surface wind forcing-related ENSO modulates the BLT variations. Key words: barrier layer thickness, interannual variability, eastern equatorial Indian Ocean, Bay of Bengal Citation: Ma Tian, Cheng Xuhua, Qi Yiquan, Chen Jiajia. 2020. Interannual variability in the barrier layer and forcing mechanism in the eastern equatorial Indian Ocean and Bay of Bengal. Acta Oceanologica Sinica, 39(7): 19–31, doi: 10.1007/s13131-020-1575-3
1 Introduction The eastern equatorial Indian Ocean (EEIO) and Bay of Bengal (BoB), as parts of the Indo-Pacific warm pool, play a key role in regulating the global climate by air-sea interaction (Oppo et al., 2009). The sea surface temperature (SST) of these areas is close to or greater than 28°C except during winter, so slight SST variations lead to a strong atmospheric circulation responses, which have a significant impact on the climate and monsoon precipitation in the surrounding areas (Palmer and Mansfield, 1984; Li et al., 2001; Shankar et al., 2007; Jiang and Li, 2011). The BoB is one of the lowest salinity ocean basins in the world due to the large amount of freshwater runoff from hinterland rivers around the BoB and the abundant rainfall during the summer monsoon (Varkey et al., 1996). This injection of fresh water significantly strengthens salinity stratification in the up
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