These cloud vortices off Saint Helena Island, captured by the MODIS (Moderate Resolution Imaging Spectroradiometer instrument) in NASA’s Terra satellite. It passed over the South Atlantic Ocean on Nov. 15, 2012. Image credit: NASA/GSFC/Jeff Schmaltz/MODIS Land Rapid Response Team
St. Helena Island is a tiny island lying approximately 1,860 kilometers (1,156 miles) west of Africa. Volcanic in origin, it has rugged topography with steep, sharp peaks and deep ravines.
Wind, which can blow unimpeded for hundreds of miles across the ocean, strikes the face of the mountains, and is forced around the unyielding terrain. As it blows around the island, the air spins on the leeward side, much like a flowing river forms eddies on the downriver side of a piling. The spinning wind forms intricate – and mathematically predictable – patterns. When clouds are in the sky, these beautiful patterns become visible from above.