Rayleigh lidar observations of reduced gravity wave activity during the formation of an elevated stratopause in 2004 at Chatanika, Alaska (65°N, 147°W)

We report Rayleigh lidar measurements of nightly temperature profiles in the 40-80 km altitude region and 15 min relative density profiles in the 40-50 km altitude region at Poker Flat Research Range, Chatanika, Alaska (65 degrees N, 147 degrees W), in December, January, and February over three winters (2002-2003, 2003-2004, and 2004-2005). We characterize the gravity wave activity in terms of the measurements of buoyancy period and relative density fluctuations and estimate the potential energy density and growth of potential energy density with altitude. We use satellite and reanalysis data to analyze the synoptic structure of the stratospheric vortex and the Aleutian anticyclone, the planetary wave activity, and the mean winds. These three winters have a major stratospheric warming in 2002-2003, an extreme warming event in 2003-2004 resulting in an elevated stratopause, and no warming in 2004-2005. The gravity wave activity shows significant interannual variability, with an average potential energy density of 2.1 J/kg in 2002-2003, 1.1 J/kg in 2003-2004, and 5.7 J/kg in 2004-2005. We find a positive correlation of 0.74 between the gravity wave activity in the upper stratosphere and the winds in the lower stratosphere where the winds are lightest. The reduction in gravity wave activity in 2002-2003 relative to 2004-2005 reflects the influence of the Aleutian anticyclone that is present over Chatanika in 2002-2003 but absent in 2004-2005. The occurrence of lower gravity wave activity in 2003-2004, when the Aleutian anticyclone is present less often than in 2002-2003, supports recent modeling studies that indicate that the elevated stratopause is formed due to a reduction of gravity waves propagating upward into the mesosphere.