Interaction between a surface quasi-geostrophic buoyancy anomaly jet and internal vortices

This paper addresses the dynamical coupling of the ocean's surface and the ocean's interior. In particular, we investigate the dynamics of an oceanic surface jet, and its interaction with vortices at depth. The jet is induced by buoyancy (density) anomalies at the surface. We first focus on the jet alone. The linear stability indicates there are two modes of instability: the sinuous and the varicose modes. When a vortex in present below the jet, it interacts with it. The velocity field induced by the vortex perturbs the jet and triggers its destabilisation. The jet also influences the vortex by pushing it under a region of co-operative shear. Strong jets may also partially shear out the vortex. We also investigate the interaction between a surface jet and a vortex dipole in the interior. Again, strong jets may partially shear out the vortex structure. The jet also modifies the trajectory of the dipole. Dipoles travelling towards the jet at shallow incidence angles may be reflected by the jet. Vortices travelling at moderate incidence angles normally cross below the jet. This is related to the displacement of the two vortices of the dipole by the shear induced by the jet. Intense jets may also destabilise early and form streets of billows. These billows can pair with the vortices and separate the dipole.PostprintPeer reviewe

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

Numerical simulation of a variable-density mixing-layer

The development of a baroclinic secondary instability over the primary Kelvin-Helmholtz roll-up of a two-dimensional, variable-density mixing-layer is discussed. A particular attention is paid to the accuracy of the simulations by investigating the conservation of an invariant of the flow. Then, the influence of both the spatial and the temporal resolution on the development of the secondary instability is studied. It is concluded that the variable-density layer exhibits a strongly unstable region where vorticity has been intensified by the local acceleration coupled with the density stratification

Sexual differences in Salmon gonadotropin

International audienceSalmon (Oncorhynchus tschawytscha) GTH's were purified from a mixture of pituitaries of both sexes or from separate male and female glands. Some of their biochemical, immunological and biological properties have been compared. These hormones differed essentially in amino acid composition, especially lysine, histidine and half cystine residues, and by the presence of -amino (or -aminoiso) butyric acid in male and GTH II preparations. The same differences were found between GTH I-II and GTH male-female. Observed biochemical differences were sex-linked; they did not influence immunological and qualitative biological effects, but could determine the affinity of the GTH of each sex or its specific receptors

L'insémination artificielle de la truite Salmo gairdneri Richardson.

L'expérimentation a consisté : 1°) à diluer avant insémination le sperme ou les ovules dans des dilueurs (dNa-K) constitués de quantités variables de KCI et NaCI (Tableau 1) ou 2°) à pratiquer l'insémination directement dans ces mêmes dilueurs. Après insémination et avant transfert en eau douce, les gamètes peuvent être laissés simplement dans le dNa-K (technique de simple dilution). On peut aussi ajouter le dilueur d'insémination standard (dNa : dilueur n° 1, tableau 1) (technique de double dilution). Après dilution les spermatozoïdes restent immobilisés lorsque la concentration en KCl du dilueur dépasse 10 mmol/l. Cette immobilisation est réversible pour des concentrations en KCl comprises entre 10 et 30 mmol/l. Au contraire la fécondabilité des ovules est légèrement diminuée lorsque la concentration en KCl du dilueur atteint 10 mmol/l. Cependant des possibilités d'utilisation de la technique de double dilution lors de l'insémination artificielle de la Truite sont envisageables