Normally, NLCs begin to dim in late July, then fade away completely as August unfolds. It is their seasonal pattern. This year, though, the night-shining clouds are surging as July comes to an end.
Noctilucent clouds form when summertime wisps of water vapour rise to the top of the atmosphere and wrap themselves around specks of meteor smoke.
Mesospheric winds assemble the resulting ice crystals into NLCs.
My very first time lapse video of noctilucent clouds in Simuna, Estonia 26/07/18. The show was absolutely amazing. #shiningclouds #noctilucentclouds #nlcnow #spaceweather #Estonia #astrophotos #nlc pic.twitter.com/sZJcH5p8bU
— Kairo Kiitsak (@KairoKiitsak) July 26, 2018
In 2017 a heatwave in the mesosphere melted those crystals, causing a brief “noctilucent blackout.”
Perhaps the opposite is happening now. A cold spell in the mesosphere could be extending the season.
Another possibility is the solar cycles. Studies have shown that NLCs intensify during solar minimum.
Solar minimum conditions are in effect now, as the sun has been spotless for 31 of the past 32 days.
Further reading — here.
[Featured Photo: Kairo Kiitsak, Estonia]
[Info thanks to: www.spaceweather.com]