The Response of the Water Surface Layer to Internal Turbulence and Surface Forcing

Abstract

We have carried out an experimental study of the turbulence kinetic energy dissipation rate (ϵ), temperature dissipation rate (χ), and turbulent heat flux (THF) within the water surface layer in the presence of non-breaking wave, surface convection, and horizontal heat and eddy fluxes that play a prominent role in the front. We noted that the non-breaking wave dominates ϵ values within the surface layer. While analyzing the vertical ϵ variability, the presence of a wave-affected layer from the water surface to a depth of z≈1.25λw is observed, where λw is the wavelength. ϵ associated with non-breaking waves ranged to 4.9×10−6–7×10−6 m2/s3 for the wavelength range of 0.038 m < λw < 0.098 m categorized as the gravity and gravity-capillary wave regimes. ϵ values increase for longer λw and non-breaking wave ϵ values represent their significant contribution to the ocean energy budget and dynamic of surface layer considering that the non-breaking wave covers the large fraction of ocean surface. We also found that the surface mean square slope (MSS) and wave generated ϵ have the same order of magnitude, i.e., MSS ∼ϵ. Besides, we have documented that the small-scale temperature fluctuation change (i.e., χ) is consistent with the large-scale temperature gradient change (i.e., d<T>/dz). The value of the THF is approximately constant within the surface layer. It represents that the measured THF near the water surface can be considered a surface water THF, challenging to measure directly.

Asymmetric Frontal Response across the Gulf of Mexico Front in Winter 2016

“…Based on the VMP200 data, we estimated the surface vertical turbulent heat flux (THF) defined as: THF ≈ − 1 2 ρc P χ/T z [35,36], where the c p is water specific heat and the T z is temperature gradient. The surface is defined here as a part of the water column where the mean T z and the TD were measured by the VMP200 upcasts and represent depth average from the actual sea surface to depth 0.15 m and 0.5 m for T z and TD, respectively.…”