Impact of Evaporation on Estuarine Mixing Estimates

Recent studies linked the quantities of estuarine exchange flows to the volume integrated mixing inside the estuary, where mixing is defined as the destruction of salinity variance. The estimates use the Knudsen relations and the Total Exchange Flow (TEF) analysis framework to quantify the mixing as a function of bulk values which describe the estuarine exchange flow. These studies only included river runoff as a source of freshwater and neglected the freshwater exchange in terms of precipitation and evaporation through the surface. The latter is the necessary process to include to be able to describe inverse estuaries. Therefore, evaporation and precipitation are now included to complete the existing mixing estimates. This inclusion allows to apply the mixing estimates to all kinds of estuaries with different freshwater forcing types. We conduct idealized 2D numerical simulations of an estuary where we are able to diagnose the mixing of the model directly and compare to the results of the complete mixing estimates. We show results of different freshwater forcing types including a combination of evaporation, precipitation and river discharge. All simulations with different forcing obey the same derived estimates for the mixing.