Association between extreme atmospheric anomalies over Antarctic sea ice, Southern Ocean polar cyclones and atmospheric rivers

This study analyses the association of Southern Ocean extratropical cyclones and atmospheric rivers (ARs) with extreme temperature and/or moisture atmospheric anomalies over Antarctic sea ice. The hypothesis we test is whether the circulations associated with cyclones and ARs may routinely lead to the presence of unusually warm, moist airmasses over ice-covered regions. The analysis is conducted over the extended Austral winter seasons (May – September) between May 1979 and September 2012, based on the European Centre for Medium-Range Weather Forecasts Interim reanalysis data. Approximately 27% of intense Southern Ocean cyclones and 20% of ARs occur in the vicinity of extreme temperature anomalies, while 12% of intense cyclones and 46% of ARs occur in the vicinity of extreme moisture anomalies. We summarize our results as follows: (1) extreme atmospheric anomalies over sea ice often occur in the absence of cyclones or ARs; (2) intense cyclones have a stronger association with extreme temperature  anomalies than ARs; (3) approximately half of the ARs are in the vicinity of extreme moisture anomalies, while the latter’s link with cyclones is weak; (4) if an AR is in the vicinity of an extreme temperature anomaly, there will likely be a concurrent extreme moisture anomaly. This points to a strong association between ARs and moisture extremes, and a nuanced link between Southern Ocean polar cyclones and atmospheric anomalies over Antarctic sea ice.