Mountain wave motions determined by the Esrange MST radar

Abstract

Abstract. A European campaign of ground-based radar, lidar and optical measurements was carried out during the winter of 1996 to study lee waves in the northern part of Scandinavia. The participants operated ozone lidars, backscatter lidars and MST radars at ALOMAR/Andoya and Esrange/Kiruna, and an ALIS imaging system in Kiruna. The Andoya site was generally windward of the Scandinavian mountains, the Kiruna site on the leeward side. The goal of the experiment was to examine the in¯uence of lee waves on the formation of Polar Stratospheric Clouds (PSCs). This paper studies the radar data from MST-radar ESRAD located at Esrange [68. N, 21. E], i.e. in the lee of the mountains. We present three cases where strong lee waves were observed: in one case they propagated upwards to the lower stratosphere and in the other two cases they were trapped or absorbed in the troposphere. We examine the local waves and the direction and strength of the local wind using the radar, the synoptic meteorological situation using weather maps (European Meteorological Bulletin) and the synoptic stratospheric temperatures using ECMWF data. We observed that waves propagate up to the stratosphere during frontal passages. When anticyclonic ridges are present, the propagation to the stratosphere is very weak. This is due to trapping of the waves at or below the tropopause. We also show that the radar data alone can be used to characterise the dierent weather conditions for the three cases studied (through the variation of the height of the tropopause). The synoptic stratospheric temperatures in the three cases were similar, and were above the expected threshold for PSC formation. Lidar and visual observation of PSCs and nacreous clouds, respectively, showed that these were present only in the case when the lee waves propagated up to the lower stratosphere.

Characteristics of tropopause folds over Arctic latitudes

“…From this scenario, one can speculate that these vertical wind oscillations could be either inertio‐gravity waves (IGW) or mountain waves. ESRAD is on the eastern side of the Scandinavian ridge and a strong low‐level westerly wind often triggers mountain lee waves [ Réchou et al , 1999]. On the other hand, there is a sizable number of observations providing evidence that jets and fronts are the important sources of IGW [ Cornish and Larsen , 1989; Thomas et al , 1999, and references therein].…”

Joint radar/lidar observations of possible aerosol layers in the winter mesosphere

“…These are conditions which generally can lead to upward-propagating lee-waves (see e.g. RÃ echou et al, 1999) and there are indeed signs of a wave in the lidar temperature and buoyancy-frequency proÿles between 30 and 50 km altitude (not shown). It seems also that the winds would allow further upward propagation at least up to 80 km altitude.…”

Turbulence associated with mountain waves over Northern Scandinavia – a case study using the ESRAD VHF radar and the WRF mesoscale model

“…This radar is situated on the lee side of the Scandinavian mountain chain at 67.9 • N, 21.1 • E (see Fig. 1), and often sees the signatures of mountain waves (Réchou et al, 1999). Our aim in this study is to determine whether, with the help of a mesoscale atmospheric model, we can understand the conditions leading to the turbulence which is often seen by the radar in association with mountain waves.…”