Response of the Antarctic Stratosphere to Two Types of El Nino Events

This study is the first to identify a robust El Nino-Southern Oscillation (ENSO) signal in the Antarctic stratosphere. El Nino events between 1979 and 2009 are classified as either conventional "cold tongue" events (positive SST anomalies in the Nino-3 region) or "warm pool" events (positive SST anomalies in the Nino-4 region). The 40-yr ECMWF Re-Analysis (ERA-40), NCEP, and Modern Era Retrospective-Analysis for Research and Applications (MERRA) meteorological reanalyses are used to show that the Southern Hemisphere stratosphere responds differently to these two types of El Nino events. Consistent with previous studies, cold tongue events do not impact temperatures in the Antarctic stratosphere. During warm pool El Nino events, the poleward extension and increased strength of the South Pacific convergence zone favor an enhancement of planetary wave activity during September-November. On average, these conditions lead to higher polar stratospheric temperatures and a weakening of the Antarctic polar jet in November and December, as compared with neutral ENSO years. The phase of the quasi-biennial oscillation (QBO) modulates the stratospheric response to warm pool El Nino events; the strongest planetary wave driving events are coincident with the easterly phase of the QBO.