29 Apr 2022
29 Apr 2022
Status: this preprint is open for discussion.

Global coarse grained mesoscale eddy statistics based on integrated kinetic energy and enstrophy correlations

Imre M. Jánosi1,2, Holger Kantz1, Jason A. C. Gallas1,3, and Miklós Vincze4,5 Imre M. Jánosi et al.
  • 1Max Planck Institute for the Physics of Complex Systems, Nöthnitzer Str. 38, 01187 Dresden, Germany
  • 2University of Public Service, Faculty of Water Sciences, Department of Water and Environmental Policy, Ludovika tér 2, H-1083 Budapest, Hungary
  • 3Instituto de Altos Estudos da Paraíba, Rua Silvino Lopes 419-2502, 58039-190 João Pessoa, Brazil
  • 4von Kármán Laboratory for Environmental Flows, Eötvös Loránd University, Pázmány Péter s. 1/A, H-1117 Budapest, Hungary
  • 5MTA-ELTE Theoretical Physics Research Group, Pázmány Péter s. 1/A, H-1117 Budapest, Hungary

Abstract. Recently, Jánosi et al. introduced the concept of a “super vortex proxy” based on an observation of strong correlations between integrated kinetic energy and integrated enstrophy over a large enough surface area. When mesoscale vortices are assumed to exhibit a Gaussian shape, the two spatial integrals have particularly simple functional forms, and a ratio of them defines an effective radius of a “proxy vortex”. In the original work, the idea was tested over a restricted area in the Californian Current System. Here we extend the analysis to global scale by means of 25 years of AVISO altimetry data covering the (ice free) global ocean. The results are compared with a global vortex data base containing over 64 million of mesoscale eddies. We demonstrate that the proxy vortex representation of surface flow fields also works globally and provides a quick and reliable way to obtain coarse grained vortex statistics. Estimated mean eddy sizes (effective radii) are extracted in very good agreement with the data from the vortex census. Recorded eddy amplitudes are directly used to infer the part of kinetic energy transported by the mesoscale vortices. The ratio of total and eddy kinetic energies is somewhat higher than found in previous studies. The characteristic westward drift velocities are evaluated by a time lagged cross-correlation analysis of the kinetic energy fields. While zonal mean drift speeds are in good agreement with vortex trajectory evaluation in the latitude bands 30° S–5° S and 5° N–30° N, discrepancies are exhibited mostly at higher latitudes on both hemispheres. A plausible reason of somewhat different drift velocities obtained by eddy tracking and cross-correlation analysis is the fact that the drift of mesoscale eddies is only one component of the surface flow fields. Rossby wave activities, coherent currents, and other propagating features on the ocean surface apparently contribute to the zonal transport of kinetic energy.

Imre M. Jánosi et al.

Status: open (until 24 Jun 2022)

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Imre M. Jánosi et al.

Imre M. Jánosi et al.


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Short summary
Surface flow fields of the global oceans are dominated by so called mesoscale (50–300 km) eddies. They drift usually westward with a speed of a few km/day, transport mass, temperature, chlorophyll, debris, etc. Several methods are developed to identify and track eddies based on satellite measurements, some of them is computationally very demanding. Here we extend to global scale a recently proposed simple procedure which gives a quick coarse-grained statistics of mesoscale vortex properties.