On the Propagation of Free Topographic Rossby Waves near Continental Margins. Part 2: Numerical Model

Abstract

Ou (1980, Part 1) presented analytical solutions of free topographic Rossby waves propagating in an infinite wedge filled with a uniformly stratified fluid. We present here in Part 2 a numerical model incorporating more realistic topography and bottom friction to simulate the propagation of these waves across continental margins. Although the analytical solutions in a wedge can explain many of the wave properties observed in our numerical model, new features are introduced that have practical importance. It is found that the replacement of the apex by a finite nonreflecting shelf introduces at the shelf break an antinode in the pressure field, causing the kinetic energy to drop rapidly across the shelf break onto the shelf. It is also found that the baroclinic fringe waves excited near the slope/rise junction can cause an amphidromic point to form for shorter waves and reverse the direction of phase propagation above it. This changes the sign of the Reynolds stress locally and might have important implications on the mean flow structure generated by these waves. The baroclinic fringe waves also cause an offshore heat flux over the continental rise as in contrast to the onshore heat flux generated over the slope region due to the rigid upper surface. This heat flux divergence near the slope/rise junction can obviously contribute to a mean sinking motion there, accompanied by upwelling on both sides of it. Friction, however, generates an offshore heat flux near the bottom, and complicates this heat flux distribution. The model predictions are compared with the current and temperature data obtained south of New England during 1976. The comparisons are generally consistent, suggesting that topographic Rossby wave dynamics play an important role for the low-frequency motions over the continental rise and slope.