Impacts of CP and EP El Nino Events on the Antarctic Sea Ice in Austral Spring

Abstract

Based on observational data analyses and idealized modeling experiments, we investigated the distinctive impacts of central Pacific (CP) El Nino and eastern Pacific (EP) El Nino on the Antarctic sea ice concentration (SIC) in austral spring (September November). The tropical heat sources associated with EP El Nino and the co-occurring positive phase of the Indian Ocean dipole (IOD) excite two branches of Rossby wave trains that propagate southeastward, causing an anomalous anticyclone over the eastern Ross Amundsen Bellingshausen Seas. Anomalous northerly (southerly) wind to the west (east) of the anomalous anticyclone favors poleward (offshore) movements of sea ice, resulting in a sea ice loss (growth) in the eastern Ross Amundsen Seas (the Bellingshausen Weddell Seas). Meanwhile, the anomalous northerly (southerly) wind also advects warmer and wetter (colder and drier) air into the eastern Ross Amundsen Seas (the Bellingshausen Weddell Seas), causing surface warming (cooling) through the enhanced (reduced) surface heat fluxes and thus contributing to the sea ice melting (growth). CP El Nino, however, forces a Rossby wave train that generates an anomalous anticyclone in the eastern Ross Amundsen Seas, 208 west of that caused by EP El Nino. Consequently, a positive SIC anomaly occurs in the Bellingshausen Sea. A dry version of the Princeton atmospheric general circulation model was applied to verify the roles of anomalous heating in the tropics. The result showed that EP El Nino can remotely induce an anomalous anticyclone and associated dipole temperature pattern in the Antarctic region, whereas CP El Nino generates a similar anticyclone pattern with its location shift westward by 208 in longitudes.