Oh, the title of the article says they are creeping. Oh well. Mysterious Clouds Creeping Out of the Arctic.
They’re very pretty.
They are “night shining clouds.”
According to wikipedia that means:
Noctilucent clouds, also known as polar mesospheric clouds, are bright cloudlike atmospheric phenomena visible in a deep twilight. The name means roughly “night shining” in Latin. They are most commonly observed in the summer months at latitudes between 50Â° and 70Â° north and south of the equator.
They are the highest clouds in the Earth’s atmosphere, located in the mesosphere at altitudes of around 85 km, and are visible only when illuminated by sunlight from below the horizon while the ground and lower layers of the atmosphere are in the Earth’s shadow; otherwise they are too faint to be seen. Noctilucent clouds are not fully understood meteorological phenomena. Clouds generally are not able to reach such high altitudes, especially under such thin air pressures.