Tidally Induced Cross-frontal Mean Circulation: A Numerical Study

The linear decomposition of the circulation across a tidal front suggested by an analytical model (Dong et al. 2004) is examined using a two-dimensional numerical model. Three basic experiments are performed for a homogenous ocean, and winter and summer fronts, respectively, in which the cross-frontal circulation can be interpreted within the context of the analytical solution. Through a series of numerical experiments, the sensitivity of the circulation to tidal strength, topography horizontal scale, frontal strength, and vertical eddy viscosity are examined. The effects of assumptions in the analytical model are also examined through comparison between numerical and analytical solutions. The ratio between the tidal excursion distance to the topographical scale is crucial to the Ekman cell in the homogenous ocean. With a greater density gradient, both the Bernoulli and Ekman cells are enhanced. The uniform eddy viscosity and linearization in the analytical model maybe overestimates the bottom flow in the Ekman cell and weakens the Bernoulli cell on the shallower region, respectively. The influence of the internal tide on cross-frontal circulation is discussed.