Detection of mountain waves over Spain and the Balearic Islands in the WV7.3 channel of MSG.
24 May 2022
27 December 2004
The detection of lee clouds associated with mountain waves is an important element of operational meteorology insofar as lee clouds can indicate the presence of areas of turbulence. Usually, lee clouds can be quite easily detected in visible and infrared satellite images, but sometimes, depending on the altitude of the lee clouds, they also appear in water vapour images. The best way to detect them is to animate a sequence of images where the lee clouds tend to be stationary, as if they were attached to the mountain barrier.
A special case of mountain waves are 'trapped' mountain waves, which can propagate much farther downstream (several hundred kilometres) than non-trapped waves. The conditions for trapped waves are a very high vertical stability above the mountain tops that extends over a large area downstream, and an increase of the wind speed with height in this stable layer.
On 28–29 December 2004, an strong cyclone over the Western Mediterranean generated intense winds and turbulence over the Iberian Peninsula and the Balearic Islands. In the Meteosat-8 infrared and water vapour images below, lee clouds associated with mountain waves can be seen over Spain and the Western Mediterranean, extending far downstream from the mountain ranges that generate them. Some thin, high-level lee clouds can also be seen to the lee of the Iberian mountain range over eastern Spain. Furthermore, the WV7.3 channel shows evidence of lee mountain waves generation and related turbulence even in clear areas (e.g. in the area between Spain and the Balearic Islands). Thus, in some cases, WV7.3 images can help to identify areas of clear air turbulence (CAT).
Leewave cloudiness over Spain (Met-6, VIS, rapid scans, 3 April 2003, 08:30–11:50 UTC)
Absolute topography 300 hPa with WV7.3 image (29 Dec 2004, 00:00 UTC. Source: INM)
Absolute topography 700 hPa (28 Dec 2004, 12:00 UTC. Source: Deutscher Wetterdienst)
Radiosounding of Madrid (29 Dec 2004, 00:00 UTC. Source: Univ. of Wyoming)
Other similar cases
Mountain waves over the Alps
High-level orographic cloud pattern occurred in the lee side of the Alps, gradually seen as a pronounced feature in the Convection RGB.
Gravity waves off the Atlas Mountains
Interesting orographic cloud waves formed over the Atlas Mountains, and wider, in mid-December.