The 2019 northern hemisphere noctilucent clouds season is turning out to be the most remarkable ever.
After record strong start of the season at the end of May, NLCs were seen for the first time as low as San Francisco Bay Area, California on June 9 and throughout most of Europe since then.
This already unique season turned up another notch or two last week with an extreme, widespread outbreak of well-known electric-blue clouds on June 21, accompanied by very rare red NLCs.
"At least 80% to 90% of our sky was covered by bright electric-blue waves," reports Jacob Kuiper of Steenwijk, The Netherlands. "It was unbelievable, so bright and vast. For sure, this was the most extreme display I have seen in 35 years of observing NLCs."
This summer, extra moisture in the mesosphere has super-charged noctilucent clouds, allowing them to be sighted as far south as Rome, Italy; Los Angeles, California; and Paris, France, SpaceWeather's Dr. Tony Phillips noted.
Some observers even saw rare red NLCs on June 21. "It happened around midnight," said Marek Nikodem of Szubin, Poland. "The top of the clouds developed a reddish-purple canopy." It didn't last long, but he was able to photograph the amber crown before it faded away."
Phillips said their red color is created due to the lack of ozone, citing a 1970s research which revealed that much of the sunlight hitting noctilucent clouds first passes through Earth's ozone layer. Ozone absorbs red light, while allowing blue to pass - hence the usual color of the clouds. When the sun is hanging very low, however, reddened sunlight refracted through the dense troposphere can paint the tops of NLCs red, overwhelming the usual "ozone blue."
La Tour Eiffel est à nouveau à l'honneur sur cette image rapprochée des nuages noctiluques observés le 21 Juin 2019, jour de la #FeteDeLaMusique2019 et du #Solstice d'été.— Nuages Noctiluques France (@nlc_france) June 23, 2019
Crédit: @ptrenard Bertrand Kulik#NLCfrance #NLC pic.twitter.com/DRB8ouK7qt
My take on the #NLC visible on the night of the #SummerSolstice2019 - my usual vantage point over the motorway near to #Scunthorpe to try and get some traffic trails at the same time as the #noctilucentclouds #weather @JonMitchellITV @StormHour @Official_WXUK @NLCalerts pic.twitter.com/9tiySXmdzb— Paul Simpson (@JP_Simpson) June 22, 2019
Un plan plus large des spectaculaires noctiluque du 21.06.2019. Cela permet de voir l'ampleur, bien qu'il manque la partie au dessus de La Défense ( visible sur mon compte Flickr loicmi )#NLCfrance #NLCS @meteofrance #nlc_france @severeweatherEU #meteoparis pic.twitter.com/Mk92leKikT— Loic M (@Loic_M) June 22, 2019
#timelapse of the epic #noctilucent cloud display on Monday night my favourite #cloud since I was a kid and only the second time I've seen them! 80 km high @CloudAppSoc @ICASLeeds @AtmosScience @bbcweather @NatGeoPhotos @weatherchannel @JimCantore @severeweatherEU pic.twitter.com/b6JeySw3WK— Ben Pickering (@wx_radar) June 21, 2019
We had a little #NLCnow in #Havnsø #Denmark. A beautyful quite night :-) @NLCalerts @ADphotography24 @dartanner @mikesaltsman194 @treetanner @AngelBrise67 @AngryTheInch @chunder10 @TamithaSkov @DRVejret @GoVisitDenmark @tv2vejrcenter pic.twitter.com/zBqcaKZmwJ— Lone Athanasakis (@Lathanafoto) June 23, 2019
The first known observation of NLCs dates back to 1885, two years after the 1883 eruption of Krakatoa.
At first, they were only seen at higher latitudes, but have recently started appearing ever lower in latitudes.
Featured image: NLCs over Szubin, Poland on June 21, 2019. Credit: Marek Nikodem via SpaceWeather.com