Composite Analysis of the Effects of ENSO Events on Antarctica

Previous investigations of the relationship between El Nino-Southern Oscillation (ENSO) and the Antarctic climate have focused on regions that are impacted by both El Nino and La Nina, which favors analysis over the Amundsen and Bellingshausen Seas (ABS). Here, 35 yr (1979-2013) of European Centre for Medium-Range Weather Forecasts interim reanalysis (ERA-Interim) data are analyzed to investigate the relationship between ENSO and Antarctica for each season using a compositing method that includes nine El Nino and nine La Nina periods. Composites of 2-m temperature (T-2m), sea level pressure (SLP), 500-hPa geopotential height, sea surface temperatures (SST), and 300-hPa geopotential height anomalies were calculated separately for El Nino minus neutral and La Nina minus neutral conditions, to provide an analysis of features associated with each phase of ENSO. These anomaly patterns can differ in important ways from El Nino minus La Nina composites, which may be expected from the geographical shift in tropical deep convection and associated pattern of planetary wave propagation into the Southern Hemisphere. The primary new result is the robust signal, during La Nina, of cooling over East Antarctica. This cooling is found from December to August. The link between the southern annular mode (SAM) and this cooling is explored. Both El Nino and La Nina experience the weakest signal during austral autumn. The peak signal for La Nina occurs during austral summer, while El Nino is found to peak during austral spring.