Complexity of Mesoscale Eddy Diffusivity in the Ocean

Abstract

Mesoscale eddies, loosely defined as ocean currents on the spatial scales of tens to hundreds of kilometers, are ubiquitous in the World Ocean (Chelton et al., 2007). Relentless stirring of water by these eddies leads to large-scale transport and redistribution of many dynamically and climatically important oceanic properties ("tracers"), including heat, salinity, and anthropogenic carbon (McWilliams, 2008). As a result, mesoscale eddies play a key role in determining the current and future states of the World Ocean and the Earth Climate, as manifested by strong sensitivity of ocean and climate simulations to the magnitude and distribution of eddy transports (Gnanadesikan et al., 2013;McWilliams, 2008;Wiebe & Weaver, 1999). At the same time, vast majority of ocean components in modern climate models either completely miss the eddies or only partially resolve them (Adcroft et al., 2019;Delworth et al., 2012;Williams et al., 2015). The eddy-induced transports in these models need to be additionally expressed ("parameterized") in terms of known large-scale properties. This task requires a thorough study of eddy transport properties and their significance for tracer distributions. Below, we report on several new and important properties of the eddy transport using the framework of turbulent eddy diffusion, which is defined next.

On non-uniqueness of the mesoscale eddy diffusivity

“…It is worth noting that the non-uniqueness of -tensors is not limited to the idealised QG model but is also found in a more comprehensive general circulation model (GCM) of the entire Atlantic Ocean (Kamenkovich et al. 2021).…”