Nonlinear Geostrophic Adjustment of Density Front
Abstract
This study deals with the non-linear cyclo-geostrophic adjustment of a circular density front in a two-layer stratified fluid. Laboratory experiments and numerical simulations have been performed to investigate the dynamical evolution of a fixed volume of fresh water, initially confined within a cylinder, which is quickly released in a dense rotating fluid. This configuration corresponds to a rapid input of potential energy in a geostrophic fluid layer and reproduce some dynamical processes which occur during oceanic upwelling or stratospheric warming events. The mean adjusted state observed in laboratory is relatively well predicted by standard adjustment theory based on lagrangian conservation of potential vorticity. However, strong three-dimensional motions (plume structures and shocks) in the early stage of adjustment affects the frontal region where the density interface intersects the free surface. During the adjustment, an important part of the initial potential energy is transfered to inertia-gravity waves modes. Theses modes exhibit a non-trivial structure where the kinetic energy fluctuations are concentrated in the frontal region while significant potential energy fluctuations may occur in the central region. For all cases studied, the deviation of the density interface first oscillate at the inertial frequency. Hence, the energy released to the wave modes during the adjustment is mainly concentrated at the inertial frequency. Afterwards, frequency doubling could occur for large amplitude waves.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2001
- Bibcode:
- 2001AGUFMNG42A0404S
- Keywords:
-
- 3220 Nonlinear dynamics;
- 3384 Waves and tides;
- 4528 Fronts and jets