Shear instabilities in Internal Solitary Waves under high and low-wind regimes

Wind and Internal Solitary Waves (ISWs) are well-known to mix the ocean's surface and inner stratification, but their combined effects appear to have not yet been investigated. A large ensemble of ISWs measured off the Portuguese Coast reveals that wind and ISWs may combine to increase turbulence and mixing beyond the linear combination of their individual contributions. It is found that low bulk Richardson numbers ($Ri<\frac{1}{4}$) and temperature inversions increase respectively by nearly four-fold and an order of magnitude, when comparing ISWs propagating under high and low-wind regimes. Furthermore, depth ranges where $Ri<\frac{1}{4}$ associated with ISWs propagating with high winds are observed to extend at least between unperturbed thermocline and intermediate depths. Understanding how turbulence and mixing from ISWs and wind combine may have important implications ranging from parametrizations in ocean models to our understanding of biogeochemical processes modulated by diapycnal mixing.