Differences in heat budgets of the near‐surface Arabian Sea and Bay of Bengal: Implications for the summer monsoon

Abstract

[1] An analysis of the heat budgets of the near-surface Arabian Sea and Bay of Bengal shows significant differences between them during the summer monsoon (JuneSeptember). In the Arabian Sea the winds associated with the summer monsoon are stronger and favor the transfer of heat to deeper layers owing to overturning and turbulent mixing. In contrast, the weaker winds over the bay force a relatively sluggish oceanic circulation that is unable to overturn, forcing a heat budget balance between the surface fluxes and diffusion and the rate of change of heat in the near-surface layer. The weak winds are also unable to overcome the strong near-surface stratification because of a lowsalinity surface layer. This leads to a shallow surface mixed layer that is stable and responds quickly to changes in the atmosphere. An implication is that sea surface temperature (SST) in the bay remains higher than 28°C, thereby supporting large-scale deep convection in the atmosphere during the summer monsoon. The atmospheric heating associated with the convection plays a critical role in sustaining the monsoon winds, and the rainfall associated with it, not only over the bay but also over the Indian subcontinent, maintains a low-salinity surface layer. In the Arabian Sea the strong overturning and mixing lead to lower SST and weak convective activity, which in turn, lead to low rainfall and runoff, resulting in weak stratification that can be overcome easily by the strong monsoon winds. Thus, in both basins, there is a cycle with positive feedback, but the cycles work in opposite directions. This locks monsoon convective activity primarily to the bay.

Cyclone‐induced mixing does not cool SST in the post‐monsoon north Bay of Bengal

“…Although temperature is influenced by processes other than vertical mixing, such as cooling by turbulent heat fluxes and advection, we find that PE tot is not sensitive (changes less than 10%) to the exact choice of pre-storm and post-storm dates. Shenoi et al (2002) use climatological T and S data to calculate the potential energy PE required to uniformly mix the upper 50 m of the tropical Indian …”

Hydrography and Circulation in the Eastern Tropical Indian Ocean during April-May 2011

“…2. Shenoi et al (2002) pointed out that prior to the onset of the summer monsoon, during April-May, as a large amount of heat flows into the north Indian Ocean due to the clear sky and light winds, it becomes the warmest area in the world, with the SST exceeding 30°C over most of the region. Consistent with the previous study, the temperature distribution of the three sections shows that the temperature is very high on the surface, with a warm water core (>28°C) occupying the upper 50 m of the water column located around 81°E near the equator (Fig.…”

The cold tongue in the South China Sea during boreal winter and its interaction with the atmosphere

“…Cooling of the ocean surface is either due to oceanic processes, atmospheric dynamics, or both (Chen et al, 2003). The relative importance of the cooling mechanism is different for different geographical locations and for different seasons (Duing and Leetma, 1980;Rao et al, 1989;Rao and Sivakumar, 2000;Shenoi et al, 2002). The multiyear (2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008) averaged wind fields at 925 hPa during boreal winter (Fig.…”