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Spatiotemporal variation and mechanisms of temperature inversion in the Bay of Bengal and the eastern equatorial Indian Ocean

Abstract

In the northern Bay of Bengal, the existence of intense temperature inversion during winter is a widely accepted phenomenon. However, occurrences of temperature inversion during other seasons and the spatial distribution within and adjacent to the Bay of Bengal are not well understood. In this study, a higher resolution spatiotemporal variation of temperature inversion and its mechanisms are examined with mixed layer heat and salt budget analysis utilizing long-term Argo (2004 to 2020) and RAMA (2007 to 2020) profiles data in the Bay of Bengal and eastern equatorial Indian Ocean (EEIO). Temperature inversion exists (17.5% of the total 39 293 Argo and 51.6% of the 28 894 RAMA profiles) throughout the year in the entire study area. It shows strong seasonal variation, with the highest occurrences in winter and the lowest in spring. Besides winter inversion in the northern Bay of Bengal, two other regions with frequent temperature inversion are identified in this study for the first time: the northeastern part of the Bay of Bengal and the eastern part of the EEIO during summer and autumn. Driving processes of temperature inversion for different subregions are revealed in the current study. Penetration of heat (mean ∼25 W/m2) below the haline-stratified shallow mixed layer leads to a relatively warmer subsurface layer along with the simultaneous cooling tendency in mixed layer, which controls more occurrence of temperature inversion in the northern Bay of Bengal throughout the year. Comparatively lower cooling tendency due to net surface heat loss and higher mixed layer salinity leaves the southern part of the bay less supportive to the formation of temperature inversion than the northern bay. In the EEIO, slightly cooling tendency in the mixed layer along with the subduction of warm-salty Arabian Sea water beneath the cold-fresher Bay of Bengal water, and downwelling of thermocline creates a favorable environment for forming temperature inversion mainly during summer and autumn. Deeper isothermal layer depth, and thicker barrier layer thickness intensify the temperature inversion both in the Bay of Bengal and EEIO.

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Acknowledgements

This research was possible owing to the free availability of the Argo temperature and salinity profile of Argo Global Data Access Experiment Center. The authors would also like to thank the detailed and constructive comments from the two anonymous reviewers that guided the revision of the original manuscript.

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Correspondence to Wensheng Jiang.

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Foundation item: The Marine Scholarship of China, China Scholarship Council (CSC) for International Doctoral Students under contract No. 2017SOA016552; the National Natural Science Foundation of China under contract Nos U2106204 and 41676003.

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Chowdhury, K.M.A., Jiang, W., Liu, G. et al. Spatiotemporal variation and mechanisms of temperature inversion in the Bay of Bengal and the eastern equatorial Indian Ocean. Acta Oceanol. Sin. 41, 23–39 (2022). https://doi.org/10.1007/s13131-021-1873-4

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  • DOI: https://doi.org/10.1007/s13131-021-1873-4

Key words

  • temperature inversion
  • Bay of Bengal
  • Argo and RAMA data
  • intrusion of the Arabian Sea water
  • eastern equatorial Indian Ocean
  • penetrative heat below mixed layer depth