Distribution and driving mechanisms of temperature inversion in the Bay of Bengal: modeling approach

Observational temperature and salinity datasets are almost absent along the coastal regions, northern tip of the Bay of Bengal, and adjacent Andaman Sea, and thus, model study can give more insights in this region. However, very few model studies are done on temperature inversion and most of them are confined to the part of this bay. Thus, the main objective is to investigate the mechanism in the formation and intensification of temperature inversion utilizing a high resolution (horizontal resolution 0.07° x 0.07° with 50 vertical layer) Regional Ocean Modeling System (ROMS) in the Bay of Bengal. Monthly distribution of temperature inversion in the study area derived from ROMS model simulation is presented and compared with that of the monthly mean climatology of WOA datasets. To reveal more detailed picture of temperature inversion, daily snapshots of the distribution of temperature inversion are also derived from the model. The basin averaged mixed layer heat- and salt-budget analyses are conducted to quantify the controlling factors of the mixed layer temperature and salinity. Monthly averaged temperature inversion from model simulation exhibits seasonal cycle similar to WOA datasets. Monthly mean temperature inversion from model exhibits that it develops during June, slowly increases till October, and then becomes maximum during November to the subsequent January. Inversion weakens in February and then vanishes in March. Daily averaged distribution of temperature inversion exhibits more occurrence of inversion than monthly averaged in this bay. In the northern Bay of Bengal, mixed later salinity tendency is always negative and thus, favorable in forming temperature inversion. However, model simulation depicts that only freshwater plume induced stratification is not a single driver in forming inversion in the Bay of Bengal. The net surface heat loss dominantly controls the temperature inversion in the northern Bay of Bengal throughout the year. In the southern Bay of Bengal, the mixed layer temperature tendency and mixed layer heat flux have the similar seasonal variation pattern but their tendencies are smaller than the northern Bay of Bengal. Therefore, the haline stratification is necessary condition in forming inversion but cooling tendency in mixed layer is essential for both formation and thickening the temperature inversion layer in the Bay of Bengal almost year-round. The distribution and mechanism of temperature inversion revealed in this study are valuable for understanding the ocean ecosystem of the Bay of Bengal and the influence of climate change.