WHOI PO

Title: Lateralgradients in Salinity stratification driving differences in Diurnal Warm Layerevolution in the Bay of Bengal

Abstract: Diurnal Warm Layers (DWLs) play an important role in coupling theatmosphere and the ocean. However, observations of their lateral variability,especially in freshwater-dominated regions, remain limited. This studyinvestigates lateral variations in DWL evolution over 30 km by deployingtwo unique drifting meteorological buoys with profiling instruments duringa field campaign in the Bay of Bengal. There are differences in backgroundstratification over the profilers, which are driven primarily by a combinationof background mesoscale eddies and rain lenses caused by cold pool events. Suchgradients in background stratification and wind speeds lead to variations inobserved DWL evolution, where lower wind speeds and stratified conditions leadto shallower DWLs. Consequently, there is nearly a 28% difference in net heatcontent gained during the DWL evolution over the top 15 m as a result.Equivalent difference in subsurface turbulent heat fluxes calculated using 1-Dmodeling are O(200 W/m²), and are primarily driven by lateralvariability in stratification. These gradients also disturb the balance in theTKE budget between the production and dissipation terms in the stratified DWLcase, with the shear production term being 3 times higher in the stratifiedcase. In summary, the submesoscale and mesoscale lateral variability insalinity is significant and drives DWL variations, particularly in regions withhigh salinity gradients, such as the Bay. Hence, it needs to be parameterizedfor a better atmosphere-ocean coupling in models.