Internal wave trapping and mixing in a cold water dome

A cross-sectional nonlinear numerical model of a shallow sea basin containing a cold water dome is used to examine the influence of wind frequency and dome characteristics upon internal waves and mixing. At superinertial forcing frequencies, nonlinear effects in the frontal regions of the dome give rise to propagating internal waves which are reflected by the dome's fronts. This reflection gives a standing internal wave trapped within the dome. The spatial variability of the wave is determined by forcing frequency, stratification and dome length. The magnitude of the internal wave and the length of the dome are related to the horizontal distribution of density in the frontal region. At the inertial frequency there is little internal wave propagation, while at subinertial forcing frequencies the internal wave is trapped in the frontal region, and energy cannot radiate away. Consequently, vertical mixing is enhanced in the frontal regions, while in the center of the dome the mixed layer increases due to the vertical diffusion of the wind's momentum to depth as in a single point model. In the case of wind forcing at a superinertial frequency, there is less mixing in the frontal region with internal wave propagation leading to mixing in the center of the dome. These calculations suggest that the breakdown of cold water domes in response to winter wind events may be due to a number of mixing processes depending upon wind frequency.