Influence of the ocean surface velocity dependence of the wind stress on the dynamics of the Southern Ocean

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The objective of the proposal is to understand the influence of the surface velocity dependence of the surface wind stress on the dynamics of the Southern Ocean. Extended Summary: The dependence of the surface wind stress on the ocean surface velocity is usually neglected in studies of the ocean on the grounds that the speed of the ocean surface current is often at least one order of magnitude smaller than that of the 10 m wind. However, recent studies have shown that including the ocean surface velocity dependence leads to a dissipative effect that is comparable in magnitude to that associated with the bottom friction in the ocean. The effect of this damping is especially strong on the mesoscale eddy field leading to a reduction of around 20% in the eddy kinetic energy in models that include the ocean surface velocity dependence compared to models that do not. In the Southern Ocean, the dynamics depend crucially on the mesoscale eddy field. In particular, a southward transport associated with the eddies is required to counter the northward Ekman transport in the surface layers due to the circumpolar westerly winds. It is the slight imbalance between these two counteracting effects that drives the meridional overturning circulation (MOC) in the Southern Ocean which, in turn, is of major importance for the global climate system, including the carbon cycle. The objective of the proposal is to understand the impact of including the ocean surface velocity in the parameterisation of the surface wind stress on the dynamics of the Southern Ocean. Since we expect to find a damping of the mesoscale eddy field, there is a need to explore the impact of this damping on the mean flow (e.g. the strength of the Circumpolar Current) and on the MOC. It has also been suggested that variations in the damping play a role in determining the variability of the eddy field in the ocean. Understanding the impact of the damping is therefore important for understanding the response of the Southern Ocean to changes in the overlying wind field and to climate change.