Wind straining versus estuarine circulation: exploring the parameter space
Hans Burchard, Leibniz Institute for Baltic Sea Research (IOW), Department for Physical Oceanography and Instrumentation, Rostock, Germany, Xaver Lange, Leibniz Institute for Baltic Sea Research, Physical Oceanography and Instrumentation, Rostock, Germany and Kaveh Purkiani, University of Bremen, MARUM, Bremen, Germany
Abstract:
It is well-known that down-estuary wind straining can increase estuarine circulation whereas up-estuary wind straining can decrease or even revert estuarine circulation. Basic local parameters describing this balance are the Simpson number (scaled horizontal buoyancy gradient) and the non-dimensionalised wind stress. The ratio of the latter and the former gives a local Wedderburn number which gives an estimate of the balance between the wind force and the baroclinic pressure gradient force. We use a stationary analytical solution for the water column based on a parabolic eddy viscosity for a first exploration of this parameter space, before we apply a dynamic water column model (GOTM) to investigate this balance for tidally oscillating flow. Finally, we present results from well-validated three-dimensional model simulations with realistic forcing applied to two different estuaries, (i) a tidally energetic strongly mixed inlet in the Wadden Sea and (ii) a non-tidal strongly stratified estuary in the Baltic Sea. These model results are analysed in terms of the Simpson number, the non-dimensional wind stress and the local Wedderburn number.
