Impact of Early Winter Antarctic Sea Ice Reduction on Antarctic Stratospheric Polar Vortex

Abstract

The impact of Antarctic sea ice reduction during early austral winter on the austral winter Antarctic stratospheric polar vortex is investigated using reanalysis data set and model simulations. Both reanalysis data set and model simulations show that the reduction of Antarctic sea ice during early austral winter leads to a northward displacement of the tropospheric mid-latitude jet, resembling the negative phase of the Southern Annular Mode. Meanwhile, the reduction of sea ice induces a weaker Antarctic stratospheric polar vortex during winter, which is accompanied by a weaker polar night jet. Further analysis indicates that the Antarctic sea ice reduction could lead to a greater excitation of Rossby waves and significant positive geopotential height anomalies over the Antarctic continent. The zonal wave 1 and 2 components of geopotential height anomalies are in phase with the climatology, corresponding to enhanced upward propagation of wave activity flux in early austral winter. Meanwhile, the reduction of sea ice in early austral winter could result in a more favorable atmospheric environment for the propagation of planetary waves into the stratosphere. These processes ultimately weaken the Antarctic stratospheric polar vortex and the polar night jet in winter. The reduction of sea ice in the Amundsen Sea sector enhances the upward propagation of planetary wave, while the reduction of sea ice in the Indian Ocean sector has the opposite effect.