Composite Analysis of the Effects of ENSO Events on Antarctica

Abstract

revious investigations of the relationship between El Niño?Southern Oscillation (ENSO) and the Antarctic climate have focused on regions that are impacted by both El Niño and La Niña, 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 Niño and nine La Niña periods. Composites of 2-m temperature (T2m), sea level pressure (SLP), 500-hPa geopotential height, sea surface temperatures (SST), and 300-hPa geopotential height anomalies were calculated separately for El Niño minus neutral and La Niña 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 Niño minus La Niña 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 Niña, 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 Niño and La Niña experience the weakest signal during austral autumn. The peak signal for La Niña occurs during austral summer, while El Niño is found to peak during austral spring.