A Three-Dimensional Baroclinic Model of the Irish Sea: Formation of the Thermal Fronts and Associated Circulation

Abstract

A high-resolution, three-dimensional baroclinic shelf sea model is developed and applied to the determination of the various processes influencing the generation and position of thermal fronts and the associated circulation in the Irish Sea. The model has a horizontal grid resolution of approximately 3.6 km by 3.0 km and can resolve the thermal fronts in the region, in particular in the western Irish Sea, although the grid is not sufficiently fine to resolve small-scale features along these fronts produced by baroclinic instabilities. Using meteorological forcing from Dublin Airport (located close to the center of the region) and tidal forcing, a series of numerical experiments were performed to examine the processes influencing the location and dynamics of thermal fronts and associated circulation in the Irish Sea. The results show a reasonable qualitative agreement with observations of the thermal stratification and the associated circulation in the western Irish Sea. The ability of the model to reproduce the main features of the frontal structures in the region having been established, it is used to examine the interannual variability of the density flow field. Calculations using meteorological forcing from different years show that the western Irish Sea fronts and the associated cyclonic circulation are persistent features, although exact details of the fronts and their times of formation and breakdown show a large interannual variability. Model results also reveal a patch of thermal stratification in the northern part of the eastern Irish Sea, with northward thermal-density-driven currents in this region.