Single super-vortex as a proxy for ocean surface flow fields

Imre M Jánosi,Gábor Tóth,Jason A C Gallas,Miklós Vincze

doi:10.5194/os-15-941-2019

Abstract

Abstract. Empirical flow field data evaluation in a well-studied ocean region along the US west coast revealed a surprisingly strong relationship between the surface integrals of kinetic energy and enstrophy (squared vorticity). This relationship defines a single isolated Gaussian super-vortex, whose fitted size parameter is related to the mean eddy size, and the square of the fitted height parameter is proportional to the sum of the square of all individual eddy amplitudes obtained by standard vortex census. This finding allows very effective coarse-grained eddy statistics with minimal computational efforts. As an illustrative example, the westward drift velocity of eddies is determined from a simple cross-correlation analysis of kinetic energy integrals.

Highlights

Mesoscale eddies (MEs) are energetic, swirling, timedependent circulatory flows on a characteristic scale of around 100 km, which are observed almost everywhere in satellite altimetry data of global sea surface height (Chelton et al, 2007, 2011)
We find clear maxima at nonzero time lags indicating that total kinetic energy and enstrophy are mostly advected in the offshore region; production or loss is almost negligible
We proposed a simple description of geostrophic ocean surface flow fields by exploiting the following results

Summary

Introduction

Mesoscale eddies (MEs) are energetic, swirling, timedependent circulatory flows on a characteristic scale of around 100 km (see Fig. 1), which are observed almost everywhere in satellite altimetry data of global sea surface height (Chelton et al, 2007, 2011). The total volume transport by drifting eddies is comparable in magnitude to that of the large-scale wind-driven and thermohaline circulations (Zhang et al, 2014); MEs play a crucial role in global material and heat transport and mixing of oceans. In spite of their importance, it is far from trivial to identify and characterize MEs from remote sensing data. We demonstrate here that a single Gaussian super-vortex properly describes the empirical energy/enstrophy ratio over an extended region; the height and radius of such super-vortex are strongly related to the mean values over the same area obtained by classical vortex census

Shielded Gaussian vortices

Data analysis

Eddy census

Findings

Conclusions