photo #4574303

From way above, the puffy convective top of a Cumulonimbus calvus storm cloud appears to boil up from the turquoise ocean below. This formation, spotted from the International Space Station over Andros Island, The Bahamas, showed a mist of ice crystals forming to one side of the cloud. This was likely the remains of a pileus, a cap of cloud that can develop over the summit of a towering cloud like this as stable air overhead is lifted and cooled by its growth. As the storm develops and the cloud grows taller, it generally pushes up through the delicate pileus cap. The most dramatic and imposing of all the main cloud types, Cumulonimbus is the royalty of the cloud world. This one looks likely to develop into the most mature form, known as Cumulonimbus capillatus, where all the droplets at the top freeze and the cloud’s upper reaches spread out into a broad plume of ice crystals. Though it is hidden from view high above, we can be sure that heavy showers were falling beneath this cloud onto the sand flats of the Joulter Cays, home to many endangered shorebirds and now a national park, and the shores of Andros Island. The eternal transition of water between its various states was here glimpsed from the cupola of the ISS some 250 miles (400 km) above the planet by astronaut Bob Hines on Expedition 67