Polar mesospheric clouds over the Ukraine
Polar mesospheric clouds are wispy and elusive. They form 80 to 100 kilometers (50 to 60 miles) above the ground – far higher in the atmosphere than most ordinary clouds. Astronauts aboard the International Space Station (ISS), flying at 350 kilometers (220 miles) up, are ideally placed to observe them. ISS astronauts shot the two photos on this page on August 1, 2014 as ISS flew over the southern Ukraine.
Polar mesospheric clouds typically appear only near Earth’s poles, but during the past few decades they have appeared as far south as Colorado and Virginia. The clouds also have become brighter and thicker. Scientists think the changes are related to long-term climate change, perhaps from increasing water vapor content in the upper atmosphere.