Influence of the Southern Annular Mode on the sea ice-ocean system: the role of the thermal and mechanical forcing

[摘要] The global sea ice-ocean model ORCA2-LIM is used to investigate the impactof the thermal and mechanical forcing associated with the Southern Annular Mode(SAM) on the Antarctic sea ice-ocean system. The model isdriven by idealized forcings based on regressions between the wind stress and theair temperature at one hand and the SAM index the other hand. The wind-stress component strongly affects theoverall patterns of the ocean circulation with a northward surface drift, adownwelling at about 45° S and an upwelling in the vicinity of theAntarctic continent when the SAM is positive. On the other hand, the thermalforcing has a negligible effect on the ocean currents. For sea ice, both thewind-stress (mechanical) and the air temperature (thermal) components have asignificant impact. The mechanical part induces a decrease of the sea icethickness close to the continent and a sharp decrease of the mean sea icethickness in the Weddell sector. In general, the sea ice area alsodiminishes, with a maximum decrease in the Weddell Sea. On the contrary, thethermal part tends to increase the ice concentration in all sectors except inthe Weddell Sea, where the ice area shrinks. This thermal effect is thestrongest in autumn and in winter due to the larger temperature differencesassociated with the SAM during these seasons. The sum of the thermal andmechaninal effects gives a dipole response of sea ice to the SAM, with adecrease of the ice area in the Weddell Sea and around the AntarcticPeninsula and an increase in the Ross and Amundsen Seas during high SAMyears. This is in good agreement with the observed response of the ice coverto the SAM.

[学科分类] 海洋学与技术