A 2017 satellite photo reveals an unusual cloud “cyclone” along the coast of Spain and Portugal. Researchers remain uncertain about the precise cause of this formation, but ocean eddies and an extreme heat wave likely played significant roles.
A large cloud spiral was spotted perfectly along the west coast of the Iberian Peninsula. Scientists are unsure of the exact cause of this unusually precise shape. (Image credit: NASA Earth Observatory/MODIS)
The photo captures an unusual cloud spiral along the Iberian Peninsula’s west coast. The spiral comprises moist, cloudy sea air swirled with clear, dry land air by a phenomenon known as cyclonic rotation, which also generates tropical storms such as hurricanes and typhoons, according to NASA’s Earth Observatory. In this instance, the rotation was much slower and weaker, preventing the formation of a proper vortex and keeping the clouds from moving inland. The image has been edited to include more infrared light, highlighting the contrast between land and cloud.
Stephen Joseph Munchak, a meteorologist at NASA’s Mesoscale Atmospheric Processes Laboratory, mentioned to NASA’s Earth Observatory that the exact cause of this mid-latitude rotation remains somewhat mysterious. He suggested it could have been triggered by an eddy—a temporary, swirling water current extending deep below the ocean’s surface. An extreme heat wave in Southern Europe in July 2017, which created a significant temperature difference between the cloudy sea air and the dry land air, may have also played a role in forming the spiral. At the time, temperatures in Spain and Portugal exceeded 104 degrees Fahrenheit (40 degrees Celsius).
The clouds in the spiral are marine stratocumulus clouds, common low-lying clouds that usually stay below 6,000 feet (1,830 meters) and can cover up to 6.5% of Earth’s surface at any given time, according to the National Oceanic and Atmospheric Administration (NOAA). These clouds typically appear along the western coasts of continents, where the Coriolis effect brings cold water from the deep sea to the surface, cooling the air above and allowing water vapor to condense into clouds.
The rotating clouds in the image stretched for hundreds of miles and likely persisted for several days without releasing any precipitation, according to NASA’s Earth Observatory. Similar cloud cyclones have been observed off the Iberian coast and the western coast of Morocco, though they are usually less defined than the spiral in this photo.
