Abstract
AbstractThe thermodynamic and emissive properties of the ocean thermal skin layer are crucial contributors to air‐sea heat flux. In order to properly observe ocean surface temperature without disturbing any delicate fluid mechanical processes, thermal infrared imaging is often used. However, wind impacting the ocean surface complicates the extraction of meaningful information from thermal imagery; this is especially true for transient forcing phenomena such as wind gusts. Here, we describe wind gust‐water surface interaction through its impact on skin layer thermal and emissive properties. Two key physical processes are identified: (1) the growth of centimeter‐scale wind waves, which increases interfacial emissivity, and (2) microscale wave breaking and shear, which mix the cool skin layer with warmer millimeter‐depth water and increase the skin temperature. As more observations are made of air‐sea interaction under transient forcing, the full consideration of these processes becomes increasingly important.
Highlights
The ocean thermal boundary, or skin, layer (Ewing & McAlister, 1960; Saunders, 1967; Woodcock, 1941; Woodcock & Stommel, 1947) is critical to the transfer of heat between the ocean and the atmosphere
We present a case study to demonstrate the impact of transient wind forcing on the air‐water interface and the response of the thermal skin layer
We have presented the observation of water surface thermal front passages from two different infrared imaging platforms
Summary
The ocean thermal boundary, or skin, layer (Ewing & McAlister, 1960; Saunders, 1967; Woodcock, 1941; Woodcock & Stommel, 1947) is critical to the transfer of heat between the ocean and the atmosphere. The temperature difference across the skin layer, ΔTskin, is dependent on the net heat flux and the thickness of the aqueous thermal boundary layer, which is related to the wind stress (Saunders, 1967). The quantity ΔTskin is defined as the skin sea surface temperature (SST) minus the subskin SST (Jessup et al, 2009). The skin SST (Tskin) is the radiometric temperature measured across a very small depth of approximately 20 μm. The subskin SST (or Tsubskin) represents the temperature at the base of the thermal skin layer (~1,000 μm; Donlon et al, 2014; Donlon et al, 2007). The ocean has a cool skin layer, with the skin temperature being lower than that of the water immediately below (Katsaros, 1980)
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