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December 22, 2024 - Dust, Von Kármán Vortices, and the Cape Verde Islands
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In mid-December 2024, dust from the Sahara Desert blanketed the Cape Verde Islands, nearly obscuring the volcanic island archipelago from view. At the same time, the whipping wind created whirling patterns of white cloud downwind of the islands, helping to reveal their location.
The Cape Verde Islands lie about 400 miles (650 km) off the coast of Senegal, a country in western Africa. They are often washed by wind-borne dust that pours off of Africa and moves westward. Although dust storms can occur anytime, December and January are known for “la calima”—severe dust events— as strong seasonal winds carry sand and dust away from the Sahara.
The trails of clouds are also often viewed over the Cape Verde Islands, due to the tall height of the volcanic islands. The cloud swirls are called von Kármán vortices, a distinctive pattern that can occur when a fluid passes a tall, isolated object. The fluid splits around the object, creating a swirling eddy downwind.
Von Kármán vortices routinely appear in satellite imagery. They can occur whenever an object interrupts air flow. Cloud vortices are often spotted downwind of isolated islands including not only the Cape Verde Islands, but also the Canary Islands, near Guadalupe Island, off the coast of Chile, and in the Indian Ocean.
Image Facts
Satellite:
Terra
Date Acquired: 12/19/2024
Resolutions:
1km (768.5 KB), 500m (2.2 MB), 250m (3.3 MB)
Bands Used: 1,4,3
Image Credit:
MODIS Land Rapid Response Team, NASA GSFC
In mid-December 2024, dust from the Sahara Desert blanketed the Cape Verde Islands, nearly obscuring the volcanic island archipelago from view. At the same time, the whipping wind created whirling patterns of white cloud downwind of the islands, helping to reveal their location.
The Cape Verde Islands lie about 400 miles (650 km) off the coast of Senegal, a country in western Africa. They are often washed by wind-borne dust that pours off of Africa and moves westward. Although dust storms can occur anytime, December and January are known for “la calima”—severe dust events— as strong seasonal winds carry sand and dust away from the Sahara.
The trails of clouds are also often viewed over the Cape Verde Islands, due to the tall height of the volcanic islands. The cloud swirls are called von Kármán vortices, a distinctive pattern that can occur when a fluid passes a tall, isolated object. The fluid splits around the object, creating a swirling eddy downwind.
Von Kármán vortices routinely appear in satellite imagery. They can occur whenever an object interrupts air flow. Cloud vortices are often spotted downwind of isolated islands including not only the Cape Verde Islands, but also the Canary Islands, near Guadalupe Island, off the coast of Chile, and in the Indian Ocean.
Image Facts
Satellite:
Terra
Date Acquired: 12/19/2024
Resolutions:
1km (768.5 KB), 500m (2.2 MB), 250m (3.3 MB)
Bands Used: 1,4,3
Image Credit:
MODIS Land Rapid Response Team, NASA GSFC
