The evolution of finite Rossby number hetons

• Main Author: Jean N. Reinaud
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2009
• Subjects: North Atlantic
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.530.9391; http://www.univ-brest.fr/lpo/carton/conf/pdf/JReinaud-abstract.pdf

Vortices, or coherent volumes of anomalous potential vorticity abound in the oceans and participate to the trans-port of many properties such as heat, salinity, and many other tracers. For example, Ebbesmeyer et al. (1986) estimated a population of 1,000 to 10,000 vortices on the surface layers of the North Atlantic alone. A well-known example of such vortices are the cold rings generated by the barotropic-baroclinic destabilisation of the Gulf Stream. These cold rings may pair with deep-water anticyclonic vortices of Saragasso sea water, forming a baroclinic struc-ture called “heton”, Bane et al. (1999). Such dipolar structures are self-propagating (when disaligned in the vertical), hence leave the vicinity of the Gulf Stream. Hetons are also forming nearby the Gulf of Cadiz, see Carton et al. (2002). Recently, Reinaud & Carton (2009) investigated the linear stability and the nonlinear evolution of a family of hetons under the quasi-geostrophic approximation. In this study, the hetons consist of two cylindrical vortices (poles) aligned in the vertical, separated by a vertical gap d. Both the influence of the aspect ratio of the poles of the heton r/hv and the vertical gap d/hv are addressed in this study. r is the horizontal radius of the heton, while hv is the half-height of each pole of the heton. The quasi-geostrophic model takes the Rossby number (Ro) and the Froude number (Fr) to tend to zero (Ro ∼ Fr → 0). As a consequence, there is no dynamical difference between the behaviour of cyclonic and anticyclonic vortices. Further to this research, we investigate the nonlinear evolution of such hetons at small, yet finite Rossby number.