Estimating the air-sea gas transfer velocity from a statistical reconstruction of ocean turbulence observations

<p>Although the air-sea gas transfer velocity k is usually parameterized with wind speed, the so-called small-eddy model suggests a relationship between k and the ocean surface turbulence in the form of the dissipation rate of turbulent kinetic energy ε. However, available observations of ε from oceanographic cruises are spatially and temporally sparse. In this study, we use a Gaussian Process (GP) model to investigate the relationship between the observed profiles of ε and co-located atmospheric and oceanic fields from the ERA5 reanalysis. The model is then used to construct monthly maps of ε and to estimate the climatological air-sea gas transfer velocity from existing parametrizations. As an independent  validation,  the same model is also trained on EC-Earth3 outputs with the objective of reproducing the temporal and spatial patterns of turbulence kinetic energy as simulated by EC-Earth3. The ability to predict ε is instrumental to achieve better estimates of air-sea gas exchange that take into account multiple sources of upper ocean turbulence beyond wind stress.</p>

Destabilization of a stratified shear layer by ambient turbulence

A small eddy viscosity or mass diffusivity that varies with height has been found to have unexpected effects on the Kelvin–Helmholtz (KH) instability of a stably stratified shear layer near the neutral stability boundary. In particular, varying viscosity can increase the growth rate of the instability in contrast to the effect of uniform viscosity. Here, these results are extended to parameter ranges relevant in many geophysical and engineering contexts. We find that linearization of the viscous terms based on the assumption of weak viscosity/diffusivity is valid for non-dimensional values (inverse Reynolds number) up to ${\sim}10^{-2}$. Decreasing the Richardson number far below its critical value $1/4$ can change, or even reverse, the effects of eddy viscosity and diffusivity. A primary goal is to explain the unexpected destabilization by viscosity. Varying viscosity affects vorticity (and other fluid properties) in a manner identical to advection with an advecting velocity equal to minus the gradient of viscosity. Destabilization occurs when this viscous ‘advection’ reinforces the vorticity distribution of a growing mode.

Magnetostrictive Properties of Epoxy-Bonded Tb0,3Dy0,7Fe1,9 Composites

Tb0,3Dy0,7Fe1,9 composites attract much attention due to their large magnetostriction, and small eddy current losses. In this work intelligent polymer matrix composite materials consisting of Tb0,3Dy0,7Fe1,9 particles was obtained by mixing epoxy resin and Tb0,3Dy0,7Fe1,9 powder with grains from 38 to 106 μm. The relationships among the manufacturing technology of these materials, their microstructure, as well as their magnetostriction were evaluated. Resulting composites can extend the possibilities of application the magnetostrictive materials simultaneously reduce the cost of Tb0,3Dy0,7Fe1,9.