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<p>Temperature inversions (TI) in the northern Bay of Bengal (BoB) have considerable influence on the upper ocean thermal structure and air-sea interaction. In this study, we systematically investigate the seasonal and interannual variability of TI and associated forcing mechanisms using long-term (1958–2023) ORAS5 reanalysis dataset. The wintertime TIs display significantly large interannual variability compared to other seasons and are closely associated with the inversion layer thickness (InvLT). Composite analysis reveals that the strong TI amplitude (TIA) years are characterized by strong stratification, shallow mixed layer and thick barrier layer, whereas weak TIA years exhibit weaker stratification and a deeper mixed layer. In the strong TIA years, northward offshore surface currents along the east coast of India help to retain fresh water in the northern BoB, enhancing stratification. In contrast, during weak years, southward currents transport freshwater away, weakening the barrier layer and enhancing the mixing. The inversion layer heat budget analysis shows that surface cooling via net surface heat loss and subsurface warming through penetrative shortwave radiation are the main drivers of TI. Although, entrainment cools the base of the inversion layer, the thicker inversion layer, stronger barrier layer potential energy (BLPE), and weaker kinetic energy (KE) in the strong TIA years help retain subsurface warming and sustain strong TI. In contrast, weaker BLPE and thinner inversion layer during weak years allow mixing to disrupt subsurface warming, leading to weak TI. The results underscore the role of ocean state via surface heat flux, penetrative heat flux, and entrainment in shaping TI variability.</p>

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Unrepresented subsurface temperature inversion in the northern Bay of Bengal and associated forcing mechanisms

  • 期刊论文

  • 发表日期：

    2025年9月29日

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  • Saikat Pramanik,
  • Anant Parekh,
  • C. Gnanaseelan,
  • J. S. Chowdary,
  • Rahul U. Pai

摘要

Temperature inversions (TI) in the northern Bay of Bengal (BoB) have considerable influence on the upper ocean thermal structure and air-sea interaction. In this study, we systematically investigate the seasonal and interannual variability of TI and associated forcing mechanisms using long-term (1958–2023) ORAS5 reanalysis dataset. The wintertime TIs display significantly large interannual variability compared to other seasons and are closely associated with the inversion layer thickness (InvLT). Composite analysis reveals that the strong TI amplitude (TIA) years are characterized by strong stratification, shallow mixed layer and thick barrier layer, whereas weak TIA years exhibit weaker stratification and a deeper mixed layer. In the strong TIA years, northward offshore surface currents along the east coast of India help to retain fresh water in the northern BoB, enhancing stratification. In contrast, during weak years, southward currents transport freshwater away, weakening the barrier layer and enhancing the mixing. The inversion layer heat budget analysis shows that surface cooling via net surface heat loss and subsurface warming through penetrative shortwave radiation are the main drivers of TI. Although, entrainment cools the base of the inversion layer, the thicker inversion layer, stronger barrier layer potential energy (BLPE), and weaker kinetic energy (KE) in the strong TIA years help retain subsurface warming and sustain strong TI. In contrast, weaker BLPE and thinner inversion layer during weak years allow mixing to disrupt subsurface warming, leading to weak TI. The results underscore the role of ocean state via surface heat flux, penetrative heat flux, and entrainment in shaping TI variability.