IUGG 2003 Abstract

JSP10 Rotating and Stratified Fluids (IAPSO, IAGA, IAMAS, SEDI) Friday, July 11 AM Location: Site B, Room 21

TIME [ 1210 ] [ JSP10/11A/B21-010 ]

CYCLONE-ANTICYCLONE ASYMMETRY OF GEOPHYSICAL VON KARMAN STREET

Alexandre STEGNER(LMD, IPSL Ecole Normale Superieure, Paris.)

Gaelle PERRET(LMD, IPSL Ecole Normale Superieure, Paris.) Marie FARGE ( LMD, IPSL Ecole Normale Superieure, Paris. ) Thierry PICHON ( UME, ENSTA, Palaiseau, France. )

Unlike the classical bi-dimensional Von-Karman street, geophysical vortex street are affected by the earth rotation and the vertical stratification. We performed laboratory experiments and numerical simulations to study the specific dynamics of Von-Karman street in a rotating shallow-water layer from small (150) to intermediate (1000) Reynolds number. It is shown that ageostrophic effects (finite Rossby number) or large-scale effects (small Burger number) both induce an asymmetric vortex street. These effects occur in an oceanic context especially when the island size becomes larger than the local deformation radius. On one hand, ageostrophic effects lead to elliptical cyclones which could enhance the mixing in the near wake behind the island. On the other hand, large-scale effects, induce a long tail behind the obstacle where no vortices emerge. The vortex shedding occurs far away from the island, leading to an asymmetric vortex street with triangular cyclones.