Noctilucent Cloud Season Begins (May 2015)

by Dr. Tony Phillips (

May 23, 2015: NASA’s AIM spacecraft has spotted a luminous patch of electric-blue drifting across the Arctic Circle. The sighting marks the beginning of the 2015 season for noctilucent clouds (NLCs). “The first clouds appeared on May 19th–a bit earlier than usual,” reports Cora Randall, AIM science team member at the University of Colorado. They are located at longitude +90o in this polar image recorded by AIM’s CIPS instrument:

The first northern-hemisphere NLCs of 2015, recorded by AIM/CIPS on May 19th

“It is always good to see the beginning of another season,” says James Russell of Hampton University, principal investigator for the AIM mission. “What surprises will it bring? We will see. The clouds have never disappointed us.”

NLCs are Earth’s highest clouds. Seeded by meteoroids, they float at the edge of space more than 80 km above the planet’s surface. The clouds are very cold and filled with tiny ice crystals. When sunbeams hit those crystals, they glow electric-blue.

Noctilucent clouds first appeared in the 19th century after the eruption of super-volcano Krakatoa. At the time, people thought the clouds were caused by the eruption, but long after Krakatoa’s ash settled, the clouds remained. In those days, NLCs were a polar phenomenon confined mainly to the Arctic. In recent years they have intensified and spread with sightings as far south as Utah and Colorado. This could be a sign of increasing greenhouse gases in Earth’s atmosphere.

Data from AIM have shown that NLCs are like a great “geophysical light bulb.” They turn on every year in late spring, reaching almost full intensity over a period of 5 to 10 days. News flash: The bulb is glowing. Stay tuned for sightings.