Intensification of an eddying Southern Ocean Meridional Overturning due to the Southern Annular Mode
Résumé
Realistic regional simulations at eddying to eddy-resolving resolutions are used to investigate the role of the Southern Annular Mode (SAM) in the dynamics of the Southern Ocean. A series of sensitivity experiments are run with two synthetic interannual forcings. They correspond, on the one hand, to homogeneously intensified winds, and on the other hand to poleward intensified winds consistent with an increase in the SAM. As expected, eddies are found to mitigate the response of the Antarctic Circumpolar Current (ACC) and Meridional Overturning Circulation (MOC) to poleward intensified winds. However it is not necessarily the case that transient eddies play an increasing role with increasing winds and resolution. It is found that, as winds increase, meridional transports due to transient eddies can decrease while standing eddy transports become more efficient at balancing the wind induced overturning. In one case the role of transient eddies in the MOC reduces to almost zero. This presents new challenges for eddy flux parameterization. In addition, the ocean dynamical response induced by homogeneous wind anomalies present essential differences from those induced by poleward intensified wind anomalies. In particular, poleward intensified wind anomalies are far more efficient in accelerating the ACC than homogeneous wind anomalies. The spatial pattern of wind anomalies is found to be crucial in the Southern Ocean dynamical response to wind changes.
Domaines
Océanographie
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