O mecanismo de autopropulsão de vórtices oceânicos: uma revisão

Abstract

ABSTRACT. Oceanic eddies are effective carriers of momentum, mass, heat, of chemical and biological characteristics associated generally with their place of origin.These features exercise influence on global circulation, in the distribution of large-scale water masses and in the biology of the oceans. This influence does not only involve the transfer of energy and properties associated with the place of origin of the eddy but also their strong performance in mixing processes. The motion of eddies across the oceans are primarily driven by three factors: the self-propulsion which is intrinsic to the feature and moves it towards the west; the advection by others currents and the influence of eddies nearby. This work focuses on the first point, where the self-propulsion of isolated eddies is widely reviewed and discussed. The expression that allows the approximate calculation of the translation speed of isolated vortices is deduced. The basic equations (shallow water, the Bernoulli function and integrated meridional momentum) required for this development are presented and discussed as well as the meridional forces that act on these features in motion, where the mathematical formalism associated with each of them is also reviewed. This review shows that all isolated vortices are self-propelled towards the west, regardless of the hemisphere considered. It also shows that three meridional forces act on the eddies in motion: (1) the β force, due to the difference of the Coriolis parameter between the northern and southern hemispheres of the eddy, (2) the Coriolis force and the (3) ambient force, due to the action of the external fluid on the isolated eddy. Several analyses can be made with respect to these forces and this review also presents, as an example, a comparison of the β forces acting in anticyclonic and cyclonic eddies, with the same characteristics, moving in the southern hemisphere. It is concluded that the β force in the former is greater than the force in the latter. This study also comments aspects related with the balance of forces on particles rotating inside the eddy, where the gradient, geostrophic, quasi-geostrophic and cyclostrophic balances are discussed.Keywords: isolated oceanic eddies, drift of oceanic eddies, self-propulsion, beta (β) force, ambient force. RESUMO.Vórtices oceânicos são efetivos transportadores de momentum, massa, calor, de características químicas e biológicas associadas, em geral, com o seu local de origem. Estas feições exercem influência na circulação global, na distribuição de larga escala de massas d'água e na biologia dos oceanos. Esta influência não envolve somente transferência de energia e de propriedades associadas com o local de origem do vórtice, mas também a sua acentuada atuação em processos de mistura. O movimento dos vórtices pelos oceanosé influenciado basicamente por três fatores: a autopropulsão intrínsecaà feição, que a impulsiona no sentido oeste; a advecção por correntes externas e a influência de vórtices próximos. Para um melhor entendimento da importân...

Sobre a Variabilidade Espacial E Temporal Da Energia Cinética Turbulenta (Eke) Na Confluência Brasil-Malvinas

“…As principais formas de dissipação da EKE nessa região estão relacionadas à interação de vórtices com a batimetria e com a borda continental (ZHAI et al, 2010;AZEVEDO et al, 2012), sendo a última uma das principais fontes e sumidouros de energia de mesoescala. Zhai et al (2010) se referiram a essas áreas como "cemitérios de vórtices", uma vez que essas feições tendem a atingir as bordas continentais devido à sua autopropulsão para oeste (e.g., NOF, 1981;AZEVEDO & MATA, 2010;AZEVEDO et al, 2012).…”