Processes impacting on stratification in a region of freshwater influence: application to Liverpool Bay

Wind is shown to have an important influence on water column structure and residual circulation through a straining mechanism in the Liverpool Bay region of freshwater influence. By combining a long-term data set of water column observations collected from a mooring we estimate the horizontal gradients in temperature and salinity that are used to drive a one-dimensional turbulence model. Various combinations of the processes that impact the stratification are investigated, including the wind speed and direction, horizontal buoyancy gradient, and the tidal amplitude. From this we assess the significance of these processes and find that the effect of wind direction is important in determining water column structure. Both observations and a modeling study show that an offshore wind accelerates the development of stratification on the ebb tide and decelerates the destruction of stratification on the flood tide due to a “wind straining” process. The reverse situation occurs for an onshore wind.