||Cloud Swirls and Ripples, Guadalupe Island, Baja California |
Guadalupe Island (image left) is a volcanic edifice 35 km long that lies 240 km off the coast of Mexico's Baja California peninsula. Winds on the August day this astronaut photograph was taken were blowing from the north (left), and gave rise to a series of eddies in the atmosphere which appear as circles and swirls in the clouds downwind of the island. Known technically as a Von Karman vortex street, obstacles of any kind can set up such vortices, from islands to craters to chimneys. The size of each swirl can be judged from the length of the island. Under ideal conditions clouds make the swirls visible.
A vortex street will only form under certain conditions of air speed, atmospheric stability and obstacle size. Conditions are ideal for production of vortex streets in the vicinity of Guadalupe Island, which is known to produce them almost every day in June, July and August. The phenomenon is named after Theodore von Karman (1881-1963), a Hungarian-American engineer and fluid mechanics expert.
Also visible at image top right is a series of parallel cloud lines. Known colloquially as "gravity waves," these are ripples at the boundary between layers of slightly different density within the atmosphere.