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- ItemThe atmospheric background situation in northern Scandinavia during January/February 2003 in the context of the MaCWAVE campaign(München : European Geopyhsical Union, 2006) Blum, U.; Baumgarten, G.; Schöch, A.; Kirkwood, S.; Naujokat, B.; Fricke, K.H.The atmosphere background wind field controls the propagation of gravity waves from the troposphere through the stratosphere into the mesosphere. During January 2003 the MaCWAVE campaign took place at Esrange, with the purpose of observing vertically ascending waves induced by orography. Temperature data from the U. Bonn lidar at Esrange (68° N/21° E) and the ALOMAR RMR lidar (69° N/16° E), wind data from Esrange MST radar ESRAD, as well as wind data from the ECMWF T106 model, are used to analyse the atmospheric background situation and its effect on mountain wave propagation during January/February 2003. Critical levels lead to dissipation of vertically ascending waves, thus mountain waves are not observable above those levels. In the first half of January a minor as well as a major stratospheric warming dominated the meteorological background situation. These warmings led to a wind reversal, thus to critical level filtering and consequently prevented gravity waves from propagating to high altitudes. While the troposphere was not transparent for stationary gravity waves most of the time, there was a period of eight days following the major warming with a transparent stratosphere, with conditions allowing gravity waves generated in the lower troposphere to penetrate the stratosphere up to the stratopause and sometimes even into the lower mesosphere. In the middle of February a minor stratospheric warming occurred, which again led to critical levels such that gravity waves were not able to ascend above the middle stratosphere. Due to the unfavourable troposphere and lower stratosphere conditions for gravity wave excitation and propagation, the source of the observed waves in the middle atmosphere is probably different from orography.
- ItemPolar middle atmosphere temperature climatology from Rayleigh lidar measurements at ALOMAR (69° N)(München : European Geopyhsical Union, 2008) Schöch, A.; Baumgarten, G.; Fiedler, J.Rayleigh lidar temperature profiles have been derived in the polar middle atmosphere from 834 measurements with the ALOMAR Rayleigh/Mie/Raman lidar (69.3° N, 16.0° E) in the years 1997–2005. Since our instrument is able to operate under full daylight conditions, the unique data set presented here extends over the entire year and covers the altitude region 30 km–85 km in winter and 30 km–65 km in summer. Comparisons of our lidar data set to reference atmospheres and ECMWF analyses show agreement within a few Kelvin in summer but in winter higher temperatures below 55 km and lower temperatures above by as much as 25 K, due likely to superior resolution of stratospheric warming and associated mesospheric cooling events. We also present a temperature climatology for the entire lower and middle atmosphere at 69° N obtained from a combination of lidar measurements, falling sphere measurements and ECMWF analyses. Day to day temperature variability in the lidar data is found to be largest in winter and smallest in summer.
- ItemSimultaneous lidar observations of temperatures and waves in the polar middle atmosphere on the east and west side of the Scandinavian mountains: A case study on 19/20 January 2003(München : European Geopyhsical Union, 2004) Blum, U.; Fricke, K.H.; Baumgarten, G.; Schöch, A.Atmospheric gravity waves have been the subject of intense research for several decades because of their extensive effects on the atmospheric circulation and the temperature structure. The U. Bonn lidar at the Esrange and the ALOMAR RMR lidar at the Andøya Rocket Range are located in northern Scandinavia 250 km apart on the east and west side of the Scandinavian mountain ridge. During January and February 2003 both lidar systems conducted measurements and retrieved atmospheric temperatures. On 19/20 January 2003 simultaneous measurements for more than 7 h were possible. Although during most of the campaign time the atmosphere was not transparent for the propagation of orographically induced gravity waves, they were nevertheless observed at both lidar stations with considerable amplitudes during these simultaneous measurements. And while the source of the observed waves cannot be determined unambiguously, the observations show many characteristics of orographically excited gravity waves. The wave patterns at ALOMAR show a random distribution with time whereas at the Esrange a persistency in the wave patterns is observable. This persistency can also be found in the distribution of the most powerful vertical wavelengths. The mode values are both at about 5 km vertical wavelength, however the distributions are quite different, narrow at the Esrange with values from λz=2–6 km and broad at ALOMAR, covering λz=1–12 km vertical wavelength. In particular the difference between the observations at ALOMAR and at the Esrange can be understood by different orographic conditions while the propagation conditions were quite similar. At both stations the waves deposit energy in the atmosphere with increasing altitude, which leads to a decrease of the observed gravity wave potential energy density with altitude. The meteorological situation during these measurements was different from common winter situations. The ground winds were mostly northerlies, changed in the upper troposphere and lower stratosphere to westerlies and returned to northerlies in the middle stratosphere.