Another night, another bright display of noctilucent clouds.

Source: Spaceweather.com

“On the evening of June 17th, a large area of our sky was covered by noctilucent clouds, even directly overhead,” reports Marek Nikodem of Szubin, Poland. “Simply mysterious, beautiful, stunning, unpredictable and photogenic–this season is unbelievable.”

Noctilucent clouds over Szubin, Poland, on June 17. Credit: Marek Nikodem

Heiko Ulbricht witnessed the same display from Herzogswalde, Germany. “I have been observing noctilucent clouds for 21 years. Never before have I seen such a stunning mega-outburst! The electric-blue waves extended 50° above the horizon with many rippling structures. I was speechless.”

“What is different this year in the mesosphere?” he wonders.

The most likely answer is “Solar Minimum.” The solar cycle is currently swinging low through one of the deepest minima of the past century. Extreme ultraviolet (EUV) radiation from the sun is at its lowest level in a decade–a deficit that can lead directly to more noctilucent clouds.

Noctilucent clouds over Herzogswalde, Germany on June 17th. Credit: Heiko Ulbricht

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. EUV radiation can destroy those water molecules before they freeze. Less EUV during Solar Minimum could therefore give us more noctilucent clouds.

Coincidentally, the 2019 season for noctilucent clouds began in late May just as the sun entered a period of sustained spotlessness. There hasn’t been a sunspot for the past 30 days–a span that overlaps the recent record-setting displays. Apparently, no sunspots = a lot of electric blue.

David Aragorn

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