Kármán Vortex Streets by Cape Verde Islands – March 8th, 201016.0N 24W
The lines of swirls in the clouds trailing to the southwest below the Cape Verde islands are a phenomenon known as Kármán Vortex Streets. This term is used in fluid dynamics for a repeating pattern of swirling vortices caused by the unsteady separation of flow of a fluid over bluff bodies (in this case, the islands of the Cape Verde archipelago).
The range of Re values will vary with the size and shape of the body from which the eddies are being shed, as well as with the kinematic viscosity of the fluid. Over a large Re range (47<107 for circular cylinders) eddies are shed continuously from each side of the body, forming rows of vortices in its wake.
The alternation leads to the core of a vortex in one row being opposite the point midway between two vortex cores in the other row, giving rise to the distinctive pattern shown in the image. Ultimately, the energy of the vortices is consumed by viscosity as they move further down stream and the regular pattern disappears.