Benedikt Ehard
Department of Meteorology, Stockholm University, Sweden

Long-term lidar observations of gravity waves over northern Sweden

Time and place
Wed 2 April 2014, 10.00-10.40
Room C609, Arrhenius Laboratory, 6th floor

(This event has taken place.)


This Master thesis examines observations of gravity waves with the
Esrange lidar (68 N, 21 E). Wintertime measurements during the last
18 years are analyzed with a newly developed method for retrieving
gravity wave parameters between 30 and 65km altitude. The resulting
ca. 1500 h of data form the foundation of the study presented in
this thesis. Spectral analysis shows uniformly distributed spectra of
dominant waves between 2 and 13km vertical wavelength. Evaluating
the seasonal and the inter-annual change in gravity wave activity, high
gravity wave activity is found during November and December. Between
January and March the gravity wave activity is reduced, which
is linked to the presence of the polar vortex. Also a strong correlation
between dissipating gravity waves and the monthly mean stratopause
height is found. comparison of the mean gravity wave activity measured
by the Esrange lidar to earlier published studies reveals that the
mean gravity wave activity in wintertime is higher at Esrange than at
other stations. This is explained by the location downstream of the
Scandinavian mountain ridge. The occurrence frequency of gravity
wave activity shows a bimodal distribution which is linked to two different
processes affecting gravity wave activity at Esrange. Furthermore,
stratopause characteristics measured by the lidar are compared to
those obtained from ECMWF analysis, revealing a significantly colder
stratopause in ECMWF analysis. Additionally preliminary results from
the Gravity Wave Life Cycle campaign are shown. These results depict
gravity waves with distinct vertical wavelengths propagating from the
tropopause into the lower mesosphere.