Methods to describe barotropic vortices by global fields and vortex characteristics

Research output: Contribution to journalArticle

Abstract

Results from an experimental study of vortices in a rotating shear layer are presented. The data are in the form of maps of the instantaneous horizontal velocity field obtained by a particle tracking technique. Two fundamentally different methods to analyse time series of these velocity fields are presented and compared. One technique is the empirical orthogonal function (EOF) analysis, and the other method describes the flow field in terms of a few individual localised vortices. The flows discussed here are time-dependent two-vortex flows, which could either be described as a global mode 2 or as a collection of four unequal vortices. The results show that, while EOF analysis is a very powerful tool to detect fairly regular travelling modes or stationary features, it cannot detect local dynamics. The vortex identification technique is very good at detecting local structures and events but cannot put them into the context of a global flow structure. The comparison of the techniques shows indications that the time-dependence found in the system for low mode numbers could arise from an interaction of the large scale, global-mode flow with a local mechanism of vortex generation and shedding at a solid boundary.

Original languageEnglish
Pages (from-to)189-200
Number of pages12
JournalNonlinear Processes in Geophysics
Volume9
Issue number3-4
Publication statusPublished - 2002

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vortex
vortex flow
flow structure
flow field
experimental study
method
time series
empirical orthogonal function analysis

Cite this

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title = "Methods to describe barotropic vortices by global fields and vortex characteristics",
abstract = "Results from an experimental study of vortices in a rotating shear layer are presented. The data are in the form of maps of the instantaneous horizontal velocity field obtained by a particle tracking technique. Two fundamentally different methods to analyse time series of these velocity fields are presented and compared. One technique is the empirical orthogonal function (EOF) analysis, and the other method describes the flow field in terms of a few individual localised vortices. The flows discussed here are time-dependent two-vortex flows, which could either be described as a global mode 2 or as a collection of four unequal vortices. The results show that, while EOF analysis is a very powerful tool to detect fairly regular travelling modes or stationary features, it cannot detect local dynamics. The vortex identification technique is very good at detecting local structures and events but cannot put them into the context of a global flow structure. The comparison of the techniques shows indications that the time-dependence found in the system for low mode numbers could arise from an interaction of the large scale, global-mode flow with a local mechanism of vortex generation and shedding at a solid boundary.",
author = "Wolf-Gerrit Fruh",
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pages = "189--200",
journal = "Nonlinear Processes in Geophysics",
issn = "1023-5809",
publisher = "European Geosciences Union",
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Methods to describe barotropic vortices by global fields and vortex characteristics. / Fruh, Wolf-Gerrit.

In: Nonlinear Processes in Geophysics, Vol. 9, No. 3-4, 2002, p. 189-200.

Research output: Contribution to journalArticle

TY - JOUR

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AU - Fruh, Wolf-Gerrit

PY - 2002

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AB - Results from an experimental study of vortices in a rotating shear layer are presented. The data are in the form of maps of the instantaneous horizontal velocity field obtained by a particle tracking technique. Two fundamentally different methods to analyse time series of these velocity fields are presented and compared. One technique is the empirical orthogonal function (EOF) analysis, and the other method describes the flow field in terms of a few individual localised vortices. The flows discussed here are time-dependent two-vortex flows, which could either be described as a global mode 2 or as a collection of four unequal vortices. The results show that, while EOF analysis is a very powerful tool to detect fairly regular travelling modes or stationary features, it cannot detect local dynamics. The vortex identification technique is very good at detecting local structures and events but cannot put them into the context of a global flow structure. The comparison of the techniques shows indications that the time-dependence found in the system for low mode numbers could arise from an interaction of the large scale, global-mode flow with a local mechanism of vortex generation and shedding at a solid boundary.

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