Effects of high winds on the circulation of the using a mixed open boundary condition: the Ría de Muros, Spain

The Ría de Muros is the northernmost of the Rías Baixas, four large coastal embayments on the north-western coast of the Iberian Peninsula. In this work a 3D baroclinic model with an unconventional mixed boundary condition at the ocean boundary is implemented and applied to understand how high winds affect the circulation of the ría. This boundary condition is particularly appropriate for a combined forcing, not least when its non-tidal part is significant. The model also has the capability to deal with the alternately drying and wetting areas of the inner ría. For calibration and validation, field data of current velocity and direction, water level, wind velocity and direction, and river discharge are used. The model is forced by the seven major tidal constituents, wind and river discharge data, and thermohaline conditions at the ocean boundary based on measurements. Simulated time series of water level and current velocity are found to be in close agreement with observations. Upon validation the model is applied to determine the effects of strong winds on the circulation. For this purpose three cases are considered, all with a combined forcing: a no-wind reference case in which the model is driven by the average river discharge and M2 tide, and two wind cases, in which an NNE and a SSW wind (the prevailing directions) of 10 m s−1 is added to the previous forcing. In the no-wind case a relatively weak two-layer circulation exists, with inflow in the bottom layer and outflow in the surface layer (positive estuarine circulation). Among other effects, the NNE wind strengthens significantly this circulation pattern. Instead, the SSW wind turns the two-layer pattern into a three-layer circulation, with inflow in the surface and bottom layers and outflow in the intermediate layer.