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Study Provides New Way of Looking at Energy Exchange at the Air-Sea Boundary Layer

August 8, 2019

Scientists assessed the dynamics of heat and momentum exchange between the ocean and atmosphere to better understand how these factors influence Gulf of Mexico circulation. Specifically, they investigated how these factors constrained the heat dissipation rate (energy transferred to the atmosphere) in non-hurricane conditions during a month-long field experiment studying ocean transport processes. Analysis showed that dissipative heating in low-wind conditions can equal 20%–80% of the heat flux, suggesting that the dissipative heating is not dependent directly upon wind speed. Dissipation rates increased with the steepening of nonbreaking waves, which mechanically enhanced turbulent vertical velocities. Shear or buoyancy (depending on the atmosphere’s vertical structure at any given measurement site) was the dominant mechanism of turbulent kinetic energy (TKE) production and dissipative heating in the atmospheric surface layers sampled. These observations suggest that the traditional formula theorizing that dissipative heating is proportional to wind speed cubed overestimates the magnitude of dissipative heating.

The researchers published their findings in the Journal of the Atmospheric Sciences: Stability and sea state as limiting conditions for TKE dissipation and dissipative heating.

The atmospheric surface layer is directly adjacent to the air–sea interface, where turbulent physical processes can cause momentum transfer to surface waves and currents and, subsequently, a dissipative heat transfer to the atmosphere. This movement of heat influences the development of deep ocean currents, creating flow patterns that affect waters globally. Intensity forecasts for tropical cyclones use dissipative heating parameterizations to incorporate this heat exchange. However, there have been questions raised about the assumptions behind the parameterizations, specifically that all dissipated TKE is transferred as heat and increases the total energy in the atmosphere-ocean system.

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