Von Kármán vortex streets to the lee of the Canaries

By Xavier Calbet and Jochen Kerkmann (EUMETSAT)

The Meteosat-8 image below shows a nice case of Von Kármán vortex streets to the lee of the Canary Islands. In particular, a nice pair of vortices can be seen to the lee of Gran Canaria (see image interpretation). In the animation (see link below the image), one can see how the vortices form and how they move away from the islands.

A detailed description of Von Kármán vortices is given in the case study from 4 April 2001. Another small Von Kármán vortex can be seen in the upper left part of the image within the large field of stratocumulus clouds. This vortex is coming from Madeira Island, where it was formed some hours before by the same process. The animation that shows the spectacular flow around Madeira Island is given in the 'see also' section.

The case from 8 June 2005 also shows the importance of the horizontal and temporal resolution (1km, 15 minutes) of the Meteosat-8 images (Figure 3). In fact, the stratocumulus clouds over the Atlantic are not stationary but undergo rapid changes. For example, in addition to the Von Kármán vortices one can see how the stratocumulus clouds dissolve from east to west due to: 1) the diurnal heating of the Sun and 2) the advection of dry air at low levels (below the inversion at 925hPa) coming from the African continent.

Other interesting features are the gravity waves (waves that typically form in stratocumulus fields with stable stratification, see also Low-level gravity waves within a layer of Bénard cells) that seem to move in opposite directions: from SW to NE in the lower left part of the image and from NW to SE in the upper part of the image.

Additional content

Radiosounding Tenerife (8 June 2005, 12:00 UTC. Source: Univ. of Wisconsin)
Wind vectors and temperature at 925hPa (8 June 2005, 12:00 UTC. Source: NOAA Air Resources Laboratory)
Wind vectors and temperature at 850hPa (8 June 2005, 12:00 UTC. Source: NOAA Air Resources Laboratory)