Diapycnal diffusivities in Kelvin Helmholtz engendered turbulent mixing:
the diffusive convection regime in the Arctic Ocean
Abstract
Recent progress in the direct measurement of turbulent dissipation in
the Arctic Ocean has highlighted the need for an improved
parametrization of the turbulent diapycnal diffusivities of heat and
salt that is suitable for application in the turbulent environment
characteristic of this polar region. In support of this goal we describe
herein a series of direct numerical simulations of the turbulence
generated in the process of growth and breaking of Kelvin-Helmholtz
billows. These simulations provide the data sets needed to serve as
basis for a study of the stratified turbulent mixing processes that are
expected to obtain in the Arctic Ocean environment. The mixing
properties of the turbulence are studied using a previously formulated
procedure in which the temperature and salinity fields are sorted
separately in order to enable the separation of irreversible Arctic
mixing from reversible stirring processes and thus the definition of
turbulent diffusivities for both heat and salt that depend solely upon
irreversible mixing. These analyses allow us to demonstrate that the
irreversible diapycnal diffusivities for heat and salt are both solely
dependent on the buoyancy Reynolds number in the Arctic Ocean
environment. These are found to be in close agreement with the
functional forms inferred for these turbulent diffusivities in the
previous work of Bouffard & Boegman (2013). Based on a detailed
comparison of our simulation data with this previous empirical work, we
propose an algorithm that can be used for inferring the diapycnal
diffusivities from turbulent dissipation measurements in the Arctic
Ocean.