From SpaceWeather.com Every summer since the late 19th century, Earth’s polar skies have lit up with gossamer, electric-blue clouds, twisting and rippling in the twilight sky. They’re called noctilucent (“night-shining”) because they can be seen after dark. The origin of the clouds, which hover at the very top of Earth’s atmosphere in close proximity to space itself, is uncertain. They have been linked to causes as varied as meteoroids, climate change, and the icy exhaust of the space shuttle.
News flash: The 2010 noctilucent cloud (NLC) season has just begun in the northern hemisphere. Jesper Grønne photographed a bank of NLCs rippling over Silkeborg, Denmark, on June 1st:
“I made a 3-hour movie of the phenomenon,” says Grønne. “There was a lot of activity.” Lars Zielke of Tvis, Denmark, witnessed the same display. “They were visible due north near the horizon. The clouds were not spectacular compared to others I’ve seen, but it’s a start.”
There is a well-known correlation between noctilucent clouds and the solar cycle.
NLC activity tends to peak during (and just after) years of solar minimum, possibly because low solar activity allows the upper atmosphere to cool, promoting the growth of ice crystals that make up the clouds. With the sun slowly emerging from a century-class minimum, the stage could be set for a good season of NLC watching.
Typically, the first NLCs of spring are wan and pale, followed by better displays as summer unfolds. Browse the galleries from previous years to see what may be in the offing: 2009, 2008, 2007, 2006, 2005, 2004, 2003.
Observing tips: Look west 30 to 60 minutes after sunset when the Sun has dipped 6o to 16o below the horizon. If you see luminous blue-white tendrils spreading across the sky, you may have spotted a noctilucent cloud.
Are they a northern latitude phenomenon or can those of us living 35N see them?
Curious: Why do you say “since the late 19th century”?? Is there evidence that they actually began then, or are there just no reliable records before that time?
possible correlation with the volcano (Eyjafjallajoekull)…??????
Mostly a northern latitude phenomenon. I live at 60N (southern Norway). NLCs are quite common during the summer time here, and I believe they have become more common the last few years.
Here is a NLC display from my garden at night 05 August 2006, looking north-east. Observe the wavy patterns.
http://arnholm.org/astro/atmosphere/nlc/nlc_20060805_100pst.jpg
I have not seen any NLCs so far this summer, but I have not been looking too hard.
Here on the south coast of England we had several good sighting last summer. Not seen any so far this year yet, but here’s hoping! It’s hard to understand how the water gets up so high in the atmosphere.
I used to see these over the Atlantic enroute to London overnight. We were cruising in the upper 30’s, and they were definitely well above us, way higher than the usual cirrus. I wondered if they were up in sunlight and not glowing on their own. That high, they wouldn’t be getting any of the dust filtered light that makes for red sunsets.
OT – the SpaceX Falcon 9 rocket blasts of successfully despite attack by monster insect:
http://news.bbc.co.uk/2/hi/science_and_environment/10209704.stm
I wonder how high those noctos are ? They must really warm up the ground at night being that high and all.
I’m glad we don’t get noctilucents in California; it’s hot enough here anyway without extra heating from high clouds.
Sure do look pretty though.
Very high clouds.
Free.
Very high clouds varying by year due to unknown causes.
Free.
Very high clouds not in very expensive AGW-inspired simplistic modesl of CGM computer simulations of global catastrophy.
Free.
Accuracy of 100 year and 200 year global circulation models?
Worthless.
Its not scientific, but my thoughts on noctilucents is that they are an anticyclonic feature.
During an anticyclone, you can get layers of very stable air of differing densities, and these are capable of ducting HF radio waves (curving them around the Earth). Are these high pressures doing the same to light (just as a curving ‘beam’ of water can curve light)?
From 50 deg north, the Sun would be some 16 degs below the northern horizon at midnight. This would mean that the noctilucent clouds would have to be inordinately high to catch the Sun directly, so the light must be ducted around the curvature of the Earth.
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Tenuc-
One astronomical theory suggests that we are constantly being bombarded by what are essentially snowballs, so quite a lot of water will be made available at such huge altitudes (About 50 miles/ 80Km)
Here’s a website for all Noctilucnet fans!
http://www.kersland.plus.com/
There is some wildly disruptive science that nobody wants to deal with because it so fundamentally threatening to almost every branch of science. The work Louis Frank did thirty years ago at the University of Iowa where he discovered a flux of small comets, http://smallcomets.physics.uiowa.edu/www/faq.htmlx constantly entering the earth’s atmosphere. That is how the water vapor gets up so high to form noctilucent clouds – it comes from the outside. Fascinating stuff – you should go to the web site I linked to or Google “small comets”
“They have been linked to causes as varied as meteoroids, climate change, and the icy exhaust of the space shuttle.”
_______________________
This statement, in the AGW climate era, raises the question “Why haven’t the warmists gone after NASA, and the ESA, and the Russian Space Agency, and the Japanese, etc., with more anger and lust-o?” If anyone is polluting the upper atmosphere and causing problems with the climate, it has to be these guys. (I have a feeling that the Bowing 747 is more responsible though.) But when you think of it, the Rocket Boys & Girls are the biggest polluters of the upper atmosphere, right? Don’t tell Fat Albert I said that, he might put 1+1 together.!
Personally I can’t believe that these are still being called a mystery. The earth passes through H and O ENA streams in the summer months of both the NH and SH. The survival probababilities of ENA’s arriving from the outer edges of the heliosphere @ 1AU are directly correlated to the solar cycle. See the IBEX mission. You don’t even have to read the actual research papers (yawn), they have diagrams of the earths orbit passing though these streams. But instead of explanations of NLCs that could be understood by a fifth grader, people posit ridiculous theories.
Space shuttle exhaust? Really? In the 1890’s?!?
Space snowballs? Who’s throwing them at us? Did they only start entering the atmosphere in the late 18oo’s?
AGW? In the mesosphere? In the 1890’s?
I think I’ll stick with Occam’s Razor. Raw material + time of year + solar cyle. Check the IBEX mission.
The actual number of particles entering the heliosphere should be directly dependent on the density of the stellar cloud through which the solar system is traveling, leading to external variability as well, which could range in scale from days to multiple millenia, and would readily explain NLCs not having been noticed prior to the late 1800’s.
Thank you guys for shedding some insights. I actually observed clouds like this before and only this time I have learned the name of it. I don’t have a background and profession like yours so I just think of that what I have seen is just a wonder of God. But science speaks . . . thanks again.