The Arctic Middle Atmosphere in the Earth System: IPY Observations and Recent Model Results

During both of the recent International Polar Year (IPY) northern hemisphere winters (2007-2008 and 2008-2009) the circulation of the Arctic middle atmosphere was disturbed by major warmings that resulted in record-breaking winter temperatures. In both years the stratospheric vortex was disrupted, being displaced in 2007-2009 and split in 2009-2010. While it is well known that the interannual variability in the wintertime Arctic middle atmosphere is very large, there has been an increase in the frequency of midwinter warmings in recent years, and the variations in the past two winters are widely considered to be exceptional. We present observations of the Arctic middle atmosphere and these stratospheric warmings from lidars and satellites during the IPY. We combine these observations with reanalysis data to study coupling between the Arctic middle atmosphere and both the troposphere and lower latitudes. We discuss the current state of the Arctic middle atmosphere in terms of recent climate model investigations of the response to the middle atmosphere circulation to increases in greenhouse gases.