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

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

doi:10.5194/os-15-941-2019

Cited by 2 publications

(8 citation statements)

References 39 publications

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“…The color coding in Fig. 2 indicates stronger correlations for larger tile sizes, which is in full agreement with the result in Jánosi et al (2019). Somewhat surprising is the fact that strong correlations between I EKE (t) and I Z (t) appear in several ocean basins at the smallest tile size of 1.25 • × 1.25 • , mostly at the eastern boundaries of the basins (south to Australia and around the Agulhas, Antarctic Circumpolar, Gulf, and Kuroshio Current).…”

Section: Correlations Between I Eke (T) and I Z (T) Vortex Radiisupporting

confidence: 87%

“…In this work we extend a previous analysis by Jánosi et al (2019) to the global scale based on the observation that integrated EKE and integrated enstrophy over a large enough area are strongly correlated in time. A coarse-grained approach can reveal useful information such as mean eddy size or the fraction of vortex energy in total EKE, similarly to a recent study by Rai et al (2021) wherein oceanic eddy killing by wind was analyzed.…”

Section: Introductionmentioning

confidence: 80%

“…( 2) in cylindrical coordinates, as usual. We do not repeat all the details described in Jánosi et al (2019); we just recall the most important observations. For an isolated Gaussian vortex, the total eddy kinetic energy and enstrophy are finite over an infinite domain of integration (written in 2D polar coordinates):…”

Section: Gaussian Mesoscale Eddiesmentioning

confidence: 99%

“…The plausible explanation is that a single velocity vector per grid cell (assumed to be a characteristic value over the cell) cannot resolve finer structures, and therefore the kinetic energy and enstrophy change almost independently in time. We analyzed this question in detail in Jánosi et al (2019). On the global scale, an analogously detailed analysis would be too computationally expensive to perform.…”

Section: Analysis Of Correlationsmentioning

confidence: 99%

“…Then we demonstrate the presence of strong correlations between integrated kinetic energy and enstrophy, and we obtain effective "proxy vortex" radii globally. (In Jánosi et al, 2019, the term "super vortex" was coined to characterize the surface flow field by a single Gaussian vortex; here we rather use proxy vortex to avoid overstatement.) Note that we restrict our analysis to 2D surface flow fields, and vertical vortex structures are not considered.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2022

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Abstract. Recently, Jánosi et al. (2019) introduced the concept of a “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 database containing over 64 million 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 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 30–5∘ S and 5–30∘ N, discrepancies are exhibited mostly at higher latitudes on both hemispheres. A plausible reason for 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.

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Section: Correlations Between I Eke (T) and I Z (T) Vortex Radiisupporting

confidence: 87%

Section: Introductionmentioning

confidence: 80%

Section: Gaussian Mesoscale Eddiesmentioning

confidence: 99%

Section: Analysis Of Correlationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

et al. 2022

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

Jánosi

Kantz

Gallas

et al. 2022

Preprint

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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.

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

Cited by 2 publications

References 39 publications

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

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

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

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