Observed El Nino-Southern Oscillation temperature signal in the stratosphere

Studies of stratospheric temperature variability typically include seasonal, quasi-biennial oscillation, solar, and volcanic effects, but the response to El Nino-Southern Oscillation (ENSO) is less well recognized. Modeling work suggests that ENSO may produce effects on surface climate at high latitudes by interaction with the polar stratosphere, yet until recently, past work has often failed to find a statistically significant ENSO response in polar stratospheric temperature observations. Using zonal mean temperatures from several improved radiosonde data sets beginning in 1958, we show a significant El Nino cooling signal in the tropical stratosphere and warming signal in the Arctic stratosphere in winter. In the tropical stratosphere the difference of more than 1 K between El Nino and La Nina temperatures is similar in magnitude to the tropospheric warming signal. The significant signal, derived from regression analysis, of more than 4 K in the winter Arctic stratosphere is generally largest in the lower stratosphere and extends into the upper troposphere. The signal, with a maximum in late winter, accounts for 14% to 25% of stratospheric temperature variability at 100 mbar in Arctic winter in radiosonde and reanalysis data. Satellite-derived temperatures show significant El Nino cooling in the tropical stratosphere in boreal winter, but the warming signal in the Arctic stratosphere is not statistically significant in that data set.