Decadal Variability in the Impact of ENSO on the Antarctic Peninsula

David H. Bromwich and Zhichang Guo
Polar Meteorology Group, Byrd Polar Research Center
Ohio State University, Columbus, Ohio

Atmospheric reanalyses from the European Centre for Medium-Range Weather Forecasts (ECMWF) and the National Centers for Environmental Prediction (NCEP) are used to explore the impact of the El Nino-Southern Oscillation (as monitored by the Southern Oscillation Index, SOI) in high southern latitudes, and in particular the Antarctic Peninsula-Drake Passage-southern South America region. Because both reanalyses have shortcomings over and around Antarctica, we look for robust features shown when we perform the same evaluation on both data sets. Further we concentrate on the last two decades for which there are modern satellite observations for the Southern Ocean. We merge ECMWF operational analyses after 1991 with ECMWF reanalysis data (ERA-15) prior to 1991. We compare the spatial distribution of the linear correlation coefficients between the SOI and various fields: mean sea level pressure, near-surface temperature, 500-hPa geopotential height, 200-hPa geopotential height, and 200-hPa zonal wind that monitors the behavior of the polar front jet stream. We use annual running means for evaluation to eliminate the seasonal variability and focus on the interannual time scales characteristic of ENSO. There are large differences between the 1980s and the 1990s with the ENSO-related variability being much more pronounced in the 1990s. During La Nina events in the 1990s there were lower sea level pressures and mid to upper tropospheric geopotential heights in the Drake Passage, with weaker 200-hPa zonal winds affecting the Antarctic Peninsula and stronger 200-hPa zonal winds affecting the southern tip of South America. The physical basis for the decadal variability in the teleconnection between the tropical Pacific Ocean and the Antarctic Peninsula is discussed.