Southern hemisphere circulation anomalies associated with extreme Antarctic peninsula winter temperatures



The Southern Hemisphere reveals markedly different circulation patterns associated with extreme warm and cold Antarctic Peninsula (AP) winter temperatures. Warm winters are associated with negative 500 hPa height anomalies in the Amundsen Sea-Bellingshausen Sea (AS-BS) and positive anomalies in the South Pacific (SP) and Scotia Sea with opposing anomalies existent in cold winters. Furthermore, a switch in the relative strength of the two arms of the New Zealand split jet, the subtropical jet (STJ) and polar front jet (PFJ), occurs with the PFJ (STJ) strengthened and the STJ (PFJ) weakened in warm (cold) years leading to increased cyclonic activity in the AS-BS (SP) and a corresponding decrease in the SP (AS-BS). These hemispheric anomaly patterns bear a strong resemblance to those associated with El Niño-Southern Oscillation (ENSO) events, and their origins can be ascribed to tropical sea surface temperatures (SST) changes. However, the correspondence between warm (cold) ENSO events and cold (warm) winters is not perfect. Potential contributors to this non-linearity include intraseasonal tropical SST variations (not necessarily represented in the usual filtered ENSO indices) and the persistence of local sea ice anomalies west of the Peninsula.