Standing and Transient Eddies in the response of the Southern Ocean Meridional Overturning to the Southern Annular Mode

• Main Authors: Dufour, Carolina O., Le Sommer, Julien, Zika, Jan D., Gehlen, Marion, Orr, James C., Mathiot, Pierre, Barnier, Bernard
• Other Authors: Laboratoire des Écoulements Géophysiques et Industriels Grenoble (LEGI), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Centre National de la Recherche Scientifique (CNRS), Laboratoire des Sciences du Climat et de l'Environnement Gif-sur-Yvette (LSCE), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Institut d'Astronomie et de Géophysique Georges Lemaître (UCL-ASTR), Université Catholique de Louvain = Catholic University of Louvain (UCL)
• Format: Report
• Language: English
• Published: HAL CCSD 2012
• Subjects: [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography; Antarctic; Southern Ocean; Antarc*
• Online Access: https://hal.science/hal-00592264; https://hal.science/hal-00592264v3/document; https://hal.science/hal-00592264v3/file/manuscript.pdf

To refine understanding of how Southern Ocean responds to recent intensification of the Southern Annular Mode (SAM), a regional ocean model at two eddy-permitting resolutions was forced with two synthetic interannual forcings. The first forcing corresponds to homogeneously intensified winds, while the second concerns their poleward intensification, consistent with positive phases of the SAM. Resulting wind-driven responses differ greatly between the nearly insensitive Antarctic Circumpolar Current (ACC) and the more sensitive Meridional Overturning Circulation (MOC). As expected, eddies mitigate the response of the ACC and MOC to poleward intensified winds. However, transient eddies do not necessarily play an increasing role in meridional transport with increasing winds and resolution. As winds increase, meridional transport from standing eddies becomes more efficient at balancing wind-enhanced overturning. These results question the current paradigms on the role of eddies and present new challenges for eddy flux parameterization. Results also indicate that spatial patterns of wind anomalies are at least as important as the overall change in intensity in influencing the Southern Ocean's dynamic response to wind events. Poleward intensified wind anomalies from the positive trend in the SAM are far more efficient in accelerating the ACC than homogeneous wind anomalies.