Multi-layer Quasi-geostrophic Model Research Articles

A regional quasigeostrophic circulation model of the western North Atlantic: a model-data comparison

This paper presents the results of a long-term integration of a multilayer quasigeostrophic model of the western North Atlantic. By comparing the model simulation with available observations, the aim of this paper is no investigate the level of realism that can be attained by the circulation issued from such a model and to demonstrate that, even with the simplified quasigeostrophic physics, such a local model can reproduce well the mean and eddy circulations of this region on a long time scale. As a matter of fact, numeours features of the horizontal and vertical pattern of the circulation provided by the model are in good agreement with observations: the path of the mean surface Gulf Stream, its separation at Cape Hatteras, and the effects of its interaction with the New England Seamounts Chain (NESC); the deep western boundary current (DWBC) trajectory, the northern recirculation gyre and the deep Gulf Stream east of the NESC, the anticyclonic circulation near 35°N, 60°W suggested by Hogg et al. (1986); vertical sections of the mean velocity across the Gulf Stream; variability of the position of the Gulf Stream axis; maps of surface and bottom eddy kinetic energy (EKE), and vertical profile of EKE in the Gulf Stream. The main failure of these results is an insufficient level of instability, which explains the weakness of the Charleston bump phenomenon, an insufficient rate of ring generation and a lack of EKE in the DWBC. This point would probably be improved by the use of an increased grid resolution, and perhaps also by a variable wind forcing.

Arnol′d′s second nonlinear stability theorem for general multilayer quasi-geostrophic model

Arnol′d′s second nonlinear stability criterion for motions governed by a general multilayer quasi-geostrophic model is established. The model allows arbitrary density jumps and layer thickness, and at the top and the bottom of the fluid, the boundary condition is either free or rigid. The criterion is obtained by the establishment of the upper bounds of disturbance energy and potential enstrophy in terms of the initial disturbance field.