A Three-Dimensional Model of Density-Driven Circulation in the Irish Sea

Abstract

A semi-implicit version of the Princeton Ocean Model, ECOMsi, was used to simulate the cyclonic gyre that is found in the western Irish Sea during the spring and the summer. Mesoscale, seasonal, density-driven circulations such as this are an important component of the long-term flow in shelf seas, and they pose a challenge to coastal ocean models. Extensive comparisons are made here with observational data to assess model performance. The model successfully reproduced the development of the temperature field, and the associated density-driven currents, throughout seasonal simulations. The results demonstrate conclusively that the gyre is density-driven and reinforce the dynamical importance of strong nearbed horizontal density gradients. Maximum baroclinic currents of 0.14 m s?1 were obtained, and results showed that the regional kinetic energy due to the residual flow was 20%?25% of that due to tidal flow during periods in which density gradients were strongest. The model revealed important interactions between both wind and tide and the density structure; these interactions can direct and modulate density-driven flow.