The Role of the Southern Hemisphere Polar Cell on Antarctic Sea Ice Variability

Abstract

The study explores modes of variability in the Southern Polar Cell and their relationship with known global climate modes and Antarctic sea ice. It is found that Polar Cell is barotropic in nature and 500 hPa geo-potential height (Z 500 ) field can satisfactorily represent variability in the Polar Cell. First, three leading Empirical Orthogonal Function (EOF) modes of Z 500 account for nearly 80% of observed variability in the Polar Cell. Dominant mode (PC1 500 ) comprises of high pressure divergence zone over Antarctica. Second leading mode (PC2 500 ) is low pressure zone covering Amundsen-Bellingshausen Sea (ABS) similar to ABS low feature. A new climate mode called Polar Coastal Index (PCI) is defined, which describes more than 15% and close to 30% variability of circumpolar trough and ABS low, respectively. Out of four modes defined in this study, only PCI and PC2 500 show linear trends and clear seasonality. Interestingly, both modes are affected by modulation of ABS low due to tropical ENSO forcing. SAM signature is present in Polar Cell as PC1 500 shares large variance with it. The largest impact on sea ice comes from PC2 500 followed by PC1 500 in the Antarctic Dipole regions. However, this study suggests contemporary sea ice trends cannot be sustained, and can reverse given that trends in PCI and PC2 500 favour a reversal. These results indicate that ENSO-driven Polar Cell variability plays a crucial role influencing Antarctic sea ice as it interacts with other climate modes and leads the combined impact at the interannual time scale.