Vortex merger near a topographic slope in a homogeneous rotating fluid

This work is a contribution to the PHYSINDIEN research program. It was supported by CNRS-RFBR contract PRC 1069/16-55-150001.The effect of a bottom slope on the merger of two identical Rankine vortices is investigated in a two dimensional, quasi-geostrophic, incompressible fluid. When two cyclones initially lie parallel to the slope, and more than two vortex diameters away from the slope, the critical merger distance is unchanged. When the cyclones are closer to the slope, they can merge at larger distances, but they lose more mass into filaments, thus weakening the efficiency of merger. Several effects account for this: the topographic Rossby wave advects the cyclones, reduces their mutual distance and deforms them. This along shelf wave breaks into filaments and into secondary vortices which shear out the initial cyclones. The global motion of fluid towards the shallow domain and the erosion of the two cyclones are confirmed by the evolution of particles seeded both in the cyclone sand near the topographic slope. The addition of tracer to the flow indicates that diffusion is ballistic at early times. For two anticyclones, merger is also facilitated because one vortex is ejected offshore towards the other, via coupling with a topographic cyclone. Again two anticyclones can merge at large distance but they are eroded in the process. Finally, for taller topographies, the critical merger distance is again increased and the topographic influence can scatter or completely erode one of the two initial cyclones. Conclusions are drawn on possible improvements of the model configuration for an application to the ocean.PostprintPeer reviewe

Collision of anticyclonic, lens-like eddies with a meridonial western boundary

The collision of anticyclonic, lens-like eddies with a meridional western boundary is investigated as a function of two independent, nondimensional numbers: ß = ß0 R/f o and e = ¿/f o, where f 0 and ß0 are the Coriolis parameter and its rate of change with latitude, respectively, both evaluated at the reference latitude. R is the eddy's radius, and ¿ is its angular frequency. The numerical experiments show that in all cases there is a southward expulsion of mass proportional to both ß and e. which is estimated during the eddy-boundary interaction. The eddies are invariably deformed with the initial collision, but afterward, they reacquire a new circular shape. There is a meridional translation of the eddy along the boundary which depends exclusively on the initial ratio r = e/ß. If r > 1, the eddy goes southward, but if r <1, the eddy goes northward first and then southward. As the eddy loses mass and reacquires a new circular shape, there is a readjustment of ß and e such that ß decreases because its radius becomes smaller and e increases by energy conservation. This implies that the eddies ultimately migrate southward. A formula, derived for the meridional speed of the center of mass of the eddy is consistent with the numerical results. A physical interpretation shows that after collision a zonal force is exerted on the eddy by the wall which is balanced by a meridional migration. Nonlinearities induce a southward motion, while high ß values could produce northward motion, depending on the mass distribution along the wall

Collision of anticyclonic, lens-like eddies with a meridonial western boundary

The collision of anticyclonic, lens-like eddies with a meridional western boundary is investigated as a function of two independent, nondimensional numbers: ß = ß0 R/f o and e = ¿/f o, where f 0 and ß0 are the Coriolis parameter and its rate of change with latitude, respectively, both evaluated at the reference latitude. R is the eddy's radius, and ¿ is its angular frequency. The numerical experiments show that in all cases there is a southward expulsion of mass proportional to both ß and e. which is estimated during the eddy-boundary interaction. The eddies are invariably deformed with the initial collision, but afterward, they reacquire a new circular shape. There is a meridional translation of the eddy along the boundary which depends exclusively on the initial ratio r = e/ß. If r > 1, the eddy goes southward, but if r <1, the eddy goes northward first and then southward. As the eddy loses mass and reacquires a new circular shape, there is a readjustment of ß and e such that ß decreases because its radius becomes smaller and e increases by energy conservation. This implies that the eddies ultimately migrate southward. A formula, derived for the meridional speed of the center of mass of the eddy is consistent with the numerical results. A physical interpretation shows that after collision a zonal force is exerted on the eddy by the wall which is balanced by a meridional migration. Nonlinearities induce a southward motion, while high ß values could produce northward motion, depending on the mass distribution along the wall

Adhesion by curvature of lipid tubules

Consiglio Nazionale delle Ricerche - Biblioteca Centrale - P.le Aldo Moro, 7 , Rome / CNR - Consiglio Nazionale delle RichercheSIGLEITItal

Drops of nematic liquid crystals floating on a liquid

SIGLEITItal