Mammatus clouds are an intriguing enigma of atmospheric fluid dynamics cloud physics. They’re most commonly observed beneath anvil-shaped thunderclouds. They are formed when ice crystals fall from the cumulonimbus cloud’s anvil. “The ice crystals sublimate, or change from ice to water vapour as they fall, causing the surrounding air to thermodynamically cool. The cooled air becomes negatively buoyant and begins to sink, producing the punched-out look indicative of the mammatus cloud.
Two new Aurora Borealis images were captured by Suomi NPP's Visible Infrared Imaging Radiometer Suite (VIIRS) Day/Night Band September 9, 2015. The image was produced by the Cooperative Institute for Meteorological Satellite Studies (CIMSS), located at the University of Wisconsin – Madison.
This image, which is 40 degrees across, shows the Milky Way's two dwarf galaxy companions, the Large and Small Magellanic Clouds, as they appeared to ESA's Planck spacecraft (the galaxies are the distinct blobs). Blue corresponds to low microwave emission; orange to higher microwave emission. The microwaves come from dust in star-forming regions. The contours follow the direction of the local magnetic field. Courtesy of Physics Today.