.
.
More on the mysteries behind noctilucent clouds. Lots of extra water vapour has turned up this season that can’t easily be explained.

June 19, 2019: The 2019 season for noctilucent clouds (NLCs) has been remarkable, maybe the best ever, with NLCs appearing as far south as Los Angeles CA and Albuquerque NM. What’s going on? Researchers aren’t sure, but Lynn Harvey of the University of Colorado’s Laboratory for Atmospheric and Space Physics has just found an important clue.

“The mesosphere is quite wet,” she says. “Water vapor concentrations are at their highest levels for the past 12 years.”

Noctilucent clouds over Piwnice, Poland, on June 18th. Credit: Piotr Majewski

Noctilucent clouds form when summertime wisps of water vapor rise to the top of the atmosphere. Water molecules stick to specks of meteor smoke, gathering into icy clouds that glow electric blue when they are hit by high altitude sunlight.

When noctilucent clouds began appearing at unusually low latitudes in early June, Harvey took a look at data from NASA’s Microwave…