Boundary layers at a dynamic interface: Air‐sea exchange of heat and mass

• Published in: Journal of geophysical research. Oceans 2017-04, Vol.122 (4), p.2781-2794
• Main Author: Szeri, Andrew J.
• Format: Article
• Language: English
• Subjects: Air; Air-water exchanges; air‐sea exchange; Anthropogenic factors; Boundary layer; Boundary layers; Climate studies; Downwelling; Fluctuations; Fluid flow; Gas exchange; gas transfer; Gases; Geophysics; Heat; Heat exchange; Heat flux; Heat transfer; Infrared cameras; Infrared imagery; Interfaces; Liquid phases; Ocean surface; Ocean-atmosphere interaction; Renewal; Sea surface temperature; Surface temperature; Temperature (air-sea); Thermal boundary layer; Velocity
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1002/2016JC012312

Exchange of mass or heat across a turbulent liquid‐gas interface is a problem of critical interest, especially in air‐sea transfer of natural and anthropogenic gases involved in the study of climate. The goal in this research area is to determine the gas flux from air to sea or vice versa. For sparingly soluble nonreactive gases, this is controlled by liquid phase turbulent velocity fluctuations that act on the thin species concentration boundary layer on the liquid side of the interface. If the fluctuations in surface‐normal velocity w′ and gas concentration c′ are known, then it is possible to determine the turbulent contribution to the gas flux. However, there is no suitable fundamental direct approach in the general case where neither w′ nor c′ can be easily measured. A new approach is presented to deduce key aspects about the near‐surface turbulent motions from measurements that can be taken by an infrared (IR) camera. An equation is derived with inputs being the surface temperature and heat flux, and a solution method developed for the surface‐normal strain experienced over time by boundary layers at the interface. Because the thermal and concentration boundary layers experience the same near‐surface fluid motions, the solution for the surface‐normal strain determines the gas flux or gas transfer velocity. Examples illustrate the approach in the cases of complete surface renewal, partial surface renewal, and insolation. The prospects for use of the approach in flows characterized by sheared interfaces or rapid boundary layer straining are explored. Key Points Up/downwelling ocean surface flows link readily measurable surface temperature and heat flux A new equation is developed that determines near‐surface fluid motions from such data This provides a way to use infrared image data to determine gas flux or gas transfer velocity