Oceanographic Variability and Monsoon Dynamics in the Bay of Bengal

The Bay of Bengal exhibits a unique confluence of oceanographic processes that shape South Asia’s monsoon climate and marine ecosystems. Persistent freshwater inputs from major rivers and intense monsoon rainfall create strong salinity stratification and a quasi-permanent barrier layer between the mixed layer and the thermocline. This stratification governs heat storage and vertical mixing, influencing sea surface temperature gradients that in turn modulate the monsoon Hadley circulation and rainfall distribution across the region. Seasonal wind reversals drive the Southwest and Northeast Monsoon Currents and give rise to features such as the Sri Lanka Dome, coastal upwelling cells and eddy-driven nutrient pathways that support primary productivity and fisheries. Intraseasonal variability in salinity and temperature, coupled with lateral advection, affects cyclone genesis and monsoon bursts on timescales of weeks to months. Recent observational and modelling advances are beginning to resolve these multi-scale interactions, offering improved forecasts of monsoon onset, intensity and ocean heat content with broad implications for climate adaptation and resource management.

Research from Nature Portfolio

Recent studies have achieved a full closure of the ocean mixed layer energy budget using exclusively in situ observations from the Bay of Bengal Boundary Layer Experiment. For the first time, horizontal advection and entrainment were measured to contribute significantly to sea surface temperature evolution during the monsoon, revealing that these processes are under-represented in climate models. This work provides a blueprint for extended field campaigns and highlights the necessity of integrating mixed layer dynamics into predictive frameworks to enhance monsoon rainfall forecasts and understand ocean-atmosphere feedbacks in the region.

Oceanographic Variability and Monsoon Dynamics in the Bay of Bengal publication trend

The graph below shows the total number of articles in oceanographic variability and monsoon dynamics in the bay of bengal across all publications each year (not limited to Nature Index journals).

Technical terms

Barrier layer: A salinity-stratified layer between the mixed layer and thermocline that inhibits vertical mixing.

Mixed layer: The ocean’s upper layer characterised by uniform temperature and salinity due to wind and buoyancy forcing.

Entrainment heat flux: Heat transfer into the mixed layer driven by vertical motions at its base.

Horizontal advection: Lateral transport of heat and salinity by ocean currents.

Monsoon Hadley circulation: A large-scale atmospheric circulation pattern that drives monsoon winds and rainfall.

Intraseasonal variability: Fluctuations in ocean and atmospheric properties on timescales of weeks to months.

References

1. A Study of the Mixed Layer Warming Induced by the Barrier Layer in the Northern Bay of Bengal in 2013. Remote Sensing (2024).
2. On the Influence of the Bay of Bengal’s Sea Surface Temperature Gradients on Rainfall of the South Asian Monsoon. Journal of Climate (2023).
3. Features and mechanisms of sea surface salinity intraseasonal variability in the Northern Bay of Bengal. Geoscience Letters (2024).
4. Closing the sea surface mixed layer temperature budget from in situ observations alone: Operation Advection during BoBBLE. Scientific Reports (2020).