Decadal Modulation of the Atlantic Meridional Mode on the West Antarctic Climate during Austral Winter

Abstract

Abstract Based on observations and simplified, comprehensive atmospheric models, we investigate the impact of the tropical Atlantic sea surface temperature (SST) on the West Antarctic temperature and sea ice concentration in austral winter (June–August) on decadal time scales. The tropical gradient SST anomaly (SSTA) associated with the positive phase of the Atlantic meridional mode (AMM) usually leads to cool anomalies over the Antarctic Peninsula (AP) and a dipole-like sea ice distribution, with ice growth in the Amundsen–Bellingshausen Sea and loss in the Ross Sea. When the AMM is in a positive phase, upward motion over the warm region in the North Atlantic and downward motion over the cold region in the South Atlantic strengthen the Southern Hemisphere Hadley cell, resulting in upper-level convergence over the southwestern Atlantic. This convergence induces a Rossby wave, leading to an anticyclone anomaly over the Amundsen–Bellingshausen Sea. Meridional component winds of this anticyclone anomaly are associated with wind-driven sea ice drift, temperature advection, and anomalous turbulence heat fluxes, leading to a dipole-like sea ice distribution and AP cooling. These findings are verified using two types of atmospheric models. Therefore, the AMM plays a vital role in modulating the decadal change in temperature and sea ice distribution in the West Antarctic.