Antarctic Circumpolar Wave dynamics in a simplified ocean- atmosphere coupled model

The Antarctic Circumpolar Wave (ACW) is one of the main pattern of variability in the Ocean-Atmosphere system in the southern Hemisphere extratropics. It involves sea surface temperature (SST), sea level pressure (SLP) and other variables, and consists of a wave train of zonal number 2, travelling around Antarctica at the speed of 6-8 cm s^-1, hence taking around 8 years to complete a circle. A fundamental feature of this observed pattern is that anomalies are eastward propagating and seem to be phase locked: for example SST and SLP are in quadrature (high downstream of warm SST). Nevertheless the atmospheric part of the wave has been questioned by some observational studies. Different analytical and numerical studies have veen proposed, but a convincing theoretical explanation for the ACW is still missing. In this work we study the ACW as simulated by a simple dynamical model, in order to determine the basic physical processes that characterize it. The model used is an atmospheric quasi-geostrophic tridimensional model coupled to an ocean "slab" mixed layer, which includes mean geostrophic advection by the antarctic circumpolar current (ACC). The atmosphere-ocean coupling is obtained via surface sensible heat fluxes. We analyse three configuration of the model, a "passive ocean" one, where the ocean responds to the atmopheric forcing but does not feeds back to the atmosphere; a "passive atmosphere" one, where the stationary reponse of the atmosphere to prescribed SST anomalies; and a fully coupled one. The two forced experiment show separately a positive feedback in the coupled system.The passive ocean experiment shows an ACW-type low frequency variability in the ocean, ie a propagating SST anomaly with 4 years period. SSTa amplitude created were around 0.5^C wich is less than observed anomalies (1.5^oC). This means that the stochastic focing of the atmosphere is sufficient to substain a variability of the SST whose periodicity is set by the mean advection.The passive atmosphere experiment exhibits an equivalent-barotropic response with high pressure and high air surface temperature roughly 60 to 90 degrees downstream of warm SST anomalies. This response seems to follows SST aomalies if they are made eastward propagative. We next study the fully coupled simulation to measure the effect of hte feedback on the SST anomaly propagation, the dependence on surface fluxes intensity is also studied and the relevance to observed climate discussed.