This is a good example of Von Kármán vortices that developed to the lee of the island of Madeira.
11 August 2021
06 March 2008
By Andreas Wirth and Jarno Schipper (ZAMG)
The pattern often forms on the lee side of mountainous islands during a situation with stratiform clouds (e.g. stratocumulus sheets) moving around on the east side of a sub-tropical high pressure system.
The circumstances in which these vortices' are formed are characterised by a layered buildup of the troposphere. In the layer from the surface up to 850 hPa there is usually less wind than in the 'free atmosphere'. Because there is almost no mixing between the two layers an inversion can persist for some time. Such inversions often occur in the vicinity of high pressure systems.
The island causing the vortices has to be high enough to penetrate the inversion. In addition, there need to be wind speeds of five to 15 meters per second in the lowest layer. With wind speeds less than this threshold the vortices can not develop. Higher wind speeds do not guarantee that the vortices are maintained.
Once the vortices have formed they follow the guiding airflow and dissolve when they reach an area where the temperature buildup of the troposphere is different. This pattern was first discovered in the atmosphere in 1962 with the help of the American weather satellite TIROS V, until then this feature had not been detectable in the atmosphere.
Metop-A AVHRR image (VIS0.8 channel) (11:06 UTC)
Metop-A AVHRR image (RGB NIR1.6, VIS0.8, VIS0.6) (11:06 UTC)
Aqua MODIS RGB image (bands 01-04-03) (10:15 UTC, source: NASA)
Von Kármán vortex streets to the lee of the Canary Islands (8 June 2005)
Von Kármán vortex streets to the lee of Madeira Island (6 August 2003)
Von Kármán vortex streets to the lee of the Canary Islands (4 April 2001)
Other von Kármán vortex cases
Low cloud vortices off coast of Morocco
On 10 July a low cloud vortex was spotted off the northwest coast of Morocco.
Von Kármán vortex street near Maderia
Downstream to the west of the isle of Madeira, a von Kármán vortex street can be seen.
Kármán vortex street in the mid-Atlantic
The north-east wind is disturbed over the Cape Verde islands setting up a vortex pattern downwind of the islands (tip of arrow).
Von Kármán vortex streets to the lee of Madeira
Von Kármán vortex streets to the lee of Madeira Island.
Von Kármán vortex streets to the lee of the Canaries
Von Kármán vortex streets to the lee of the Canary Islands.
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