Gravity wave activity in the Arctic stratosphere and mesosphere during the 2007-2008 and 2008-2009 stratospheric sudden warming events

We report Rayleigh lidar measurements of nightly temperature profiles in the 40-80 km altitude region and 30 min relative density profiles in the 40-50 km altitude region at Chatanika, Alaska (65 degrees N, 147 degrees W) in December, January, February, and March over two winters (2007-2008, 2008-2009). We characterize the gravity wave activity in terms of the measurements of buoyancy period and relative density fluctuations and estimate the gravity wave potential energy density. We compare these measurements with measurements at Kangerlussuaq, Greenland (67 degrees N, 51 degrees W) and Kuhlungsborn, Germany (54 degrees N, 12 degrees E). We use satellite and global meteorological data to analyze the synoptic structure of the stratospheric vortex and the Aleutian anticyclone, the planetary wave activity, and the mean winds. Major stratospheric warmings with displacement of the vortex and splitting of the vortex occurred in 2007-2008 and 2008-2009, respectively. We find a positive correlation between the gravity wave activity in the upper stratosphere and the winds in the stratosphere at all three sites. During January and February 2008, we attribute the lower average potential energy density (1.6 J/kg) at Chatanika (relative to 4.7 J/kg at Kangerlussuaq and 2.6 J/kg at Kuhlungsborn) to the blocking of gravity waves by the lower winds in the Aleutian anticyclone, while the higher value at Kangerlussuaq (where the winds are similar in strength to those at Kuhlungsborn) may reflect stronger sources of gravity waves. During February and March 2009, we attribute the lower average potential energy density (1.1 J/kg) at both Chatanika and Kuhlungsborn to the seasonal decrease of the middle atmosphere winds. In general the gravity wave activity is lowest when the wind is weak at the lowest altitudes. We compare the gravity wave activity and winds in these winters at Chatanika with the winter of 2003-2004, when an extreme warming event occurred resulting in an elevated stratopause and major reduction of gravity wave activity. We find that the 2004 warming had a stronger influence on the gravity wave activity.