19-21, February 2013 noctilucent clouds were observed in The UK, Denmark, Norway and The Netherland. Since these clouds are usually only seen in summer, it is suspected they may be the result of dust deposited in the upper atmosphere by the Chelyabinsk/Chebarkul meteor.
First, two pictures from _http://www.dmi.dk/dmi/muligt_meteorstoev_i_solnedgangen
Photo by Tom Axelsen, Copenhagen area, DK
Photo by Henrik Bondo, DK
Below are some of the links to these and similar observations
_http://spaceweather.com/gallery/indiv_upload.php?upload_id=76793&PHPSESSID=t86oearak2sckrq0kk0k91quf0 Taken by Taken by Margaret Hughes on February 19, 2013 @ Askam-in-Furness, Cumbria, England.
_http://spaceweather.com/gallery/indiv_upload.php?upload_id=76819 Same as one of the above pictures.
Taken by Tom Axelsen on February 19, 2013 @ Copenhagen, Denmark
The personal site of Tom Axelsen is: _http://grib-stjernerne.dk/ There is a discussion in Danish on the forum of the astronomical society: _http://www.astro-forum.dk/forum_posts.asp?TID=9938&PID=101708
__http://spaceweather.com/submissions/large_image_popup.php?image_name=Terry-Parker-Noctilucent-Clouds-2-of-5_1361438465.jpg Taken by Terry Parker Feb. 20, 2013 Overhead Birmingham UK
http://overhodetcom.blogspot.no/2013/02/noctilucent-clouds-in-winter.html
Taken by Julius Jahre Sætre on February 20, 2013 @ Vestfold, Norway approximately 60° North and 10° East.
_http://spaceweather.com/gallery/indiv_upload.php?upload_id=76855
Taken by Jan Tromp on February 21, 2013 @ Beverwijk, Netherlands
There is a discussion about the clouds on this site: _http://nlcnet.proboards.com/index.cgi?board=talk&action=display&thread=869
The Norwegian gave a link to an article from NASA. NASA says that meteor dust has been linked to NLCs because 3% of the NLC ice particles are formed around meteor dust. NASA also holds that the growing amount of methane is why, NLCs are seen at lower geographic altitudes. This is possible, but also, since more big meteors are observed, it follows more dust should be up there, hence more clouds.
In any case, NLCs seem to be the new need-to-know-type of cloud if one wishes to know what’s up.
The link to the article is _http://science.nasa.gov/science-news/science-at-nasa/2012/07aug_meteorsmoke/ In the article, there is also a youtube which basically reads out the article and supplements it with pictures and graphic work: _http://www.youtube.com/watch?v=Qzs9ZOsjF-c
Here are a few quotes:
_http://science.nasa.gov/science-news/science-at-nasa/2012/07aug_meteorsmoke/ said:
Specks of meteor smoke act as gathering points where water molecules can assemble themselves into ice crystals. The process is called "nucleation."
Nucleation happens all the time in the lower atmosphere. In ordinary clouds, airborne specks of dust and even living microbes can serve as nucleation sites. Tiny ice crystals, drops of water, and snowflakes grow around these particles, falling to Earth if and when they become heavy enough.
Nucleating agents are especially important in the ethereal realm of NLCs. The clouds form at the edge of space where the air pressure is little more than vacuum. The odds of two water molecules meeting is slim, and of sticking together slimmer still.
Meteor smoke helps beat the odds. According AIM data, ice crystals can grow around meteoritic dust to sizes ranging from 20 to 70 nanometers. For comparison, cirrus clouds in the lower atmosphere where water is abundant contain crystals 10 to 100 times larger.
Meteor smoke explains much about NLCs, but a key mystery remains: Why are the clouds brightening and spreading?
In the 19th century, NLCs were confined to high latitudes—places like Canada and Scandinavia. In recent times, however, they have been spotted as far south as Colorado, Utah and Nebraska. The reason, Russell believes, is climate change. One of the greenhouse gases that has become more abundant in Earth's atmosphere since the 19th century is methane. It comes from landfills, natural gas and petroleum systems, agricultural activities, and coal mining.
It turns out that methane boosts NLCs.
[…]
NLC 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've probably spotted a noctilucent cloud. Although noctilucent clouds appear most often at arctic latitudes, they have been sighted in recent years as far south as Colorado, Utah and Nebraska. NLCs are seasonal, appearing most often in late spring and summer. In the northern hemisphere, the best time to look would be between mid-May and the end of August.
Comment: The 30-60 minute gap very much depends on the time of the year. To be exact one can calculate when the sun is between 6 and 16 degrees below the horizon at a given place and at a given time. An easier way is to switch on the star programme on the computer. I have Stellarium for example. There I can turn off the Earth view and then select the azimuthal grid. Thus, I can see where the Sun is and how far it is below the horizon.
By the way the news form NASA seems to be just a reconfirmation of what was suspected/known: Peter Lancaster Brown wrote in Astronomy in Colour, published by Blanford Press London in 1972 with second revised edition from 1975 that: “Micrometeorites […] There is some evidence to suppose that such particles form the nuclei for the formation of noctilucent clouds - p. 97”