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Post by tomaxe on Feb 22, 2013 12:19:04 GMT
Hi, new member here. I saw the clouds too, from Copenhagen, Denmark. Observed the clouds from 18:05 to approximatly 18:25 CET, when they had turned a dull red. At 18:16 CET I shot some photos with my mobilphone, you can see the photos here spaceweather.com/gallery/indiv_upload.php?upload_id=76819Apparently the clouds had local sunset at 18:20 CET, from my vantage point. From this I have calculated the clouds to be in an altitude of approximatly 60 km. Regards Tom
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Post by Julius on Feb 22, 2013 19:19:42 GMT
Welcome to the forum. For the other readers here Tom was the first to spot and report about these NLC in Denmark. Could you possibly explain how one goes about calculating the height of the clouds? I have been googling all day and every NLC related paper refeers to a formula found in this book: Noctiucent clouds 1989 Michael Gadsden, Wilfried Schröder The pictures where taken within minutes of each other. I was very suprised to continue to see the NC's as the sun peaked above the horizon but they didn't stay for long after that. But yes the clouds are the same in each shot. Thank you for the clarification, much appreciated. Hi, Nice annimations. I'm glad you titled it "nlc LIKE clouds". I'm always a bit wary about such sightings. I saw the very same thing on Sunday evening! They were faint, low down cirrus combined with atmospheric haze they look just like nlc. What was the solar depresion angle? This is the key as it dictates if the right height in the atmosphere is illuminated. It's tricky! Cheers, Bill. This is what I observed after sunset on the 20.02.13. I think that is some cirrus or dust. www.youtube.com/watch?v=H1Hg4RL-7S4But I think what the others and I observed were at a much higher altitude and closely related to NLC.
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Post by ediacara on Feb 24, 2013 4:13:16 GMT
First of all I'd like to thank you all for posting the observations and sharing pics. From Hungary where I live we only had one evening without troposheric clouds, the date was 20th Feb. On this evening 3 of the Hungarian observers were looking for the possible sight of the fireball's remnants above. We only had very faint stripes on our Western sky, but still they were easily visible for the naked eye. There were no cirrus clouds present in our region. The altitude of these stripes were for sure not too high, I mean they were rather somewhere in the lower stratosphere. They became visible at the time of local sunset (actually cca. 10 minutes before it) and were still visible 40 minutes after it. They streched up to 10 degrees alt. on my sky at their best visibility. I think they resemble a bit to the SO2 clouds we could observe after the recent years' big volcanic eruptions of the Northern Hemisphere, after Kasatochi, Sarychev and Nabro. These clouds were all in the stratosphere, transported and rippled by the strong winds there (and maybe ordered by the same gravity wave process which makes the structure of NLCs or airglow). The actual observations you posted here and on SW has a good coincidence with it, but you had been much closer to the location of the greatest mass of the clouds. The fireball began its most intensive burn at the altitude of cca. 30 kms which would also make sense for its remnants being at a similar altitude. Of course this cloud also depletes a bit, so the lower stratosphere is good a place to look for it. (The blast of the fireball happened at a much lower altitude, according to the videos which showed it brightening and somewhat later the sound wave of the blast came). During the burnt of the fireball, still in the stratosphere it must have created enough nucleation seeds for the trail being so spectacular we could see on the pics and videos of it. I have seen some Russian pics of the trail taken in 3 hours after the fireball entered their atmosphere and the pics show a slow dissipation of the visible "cloud" of the trail. On the last pic it looked like a thin layer only. I have received no observation (from Russia) of any bright cloud from the evening after the fireball, neither from the morning after it. (Still have one photographer who might have some info, today I'll contact him) What my 'theory' is: the cloud you observed was not an NLC in any aspect, but rather some stratospheric cloud. Also it is cold enough in the stratosphere at winter to keep the amount of water frozen on the nucleation seeds of the fireball's remnants. The whole process is similar to a volcanic eruption's sulphuric acid cloud also in the stratosphere. We know that those volcanic clouds travel to great distances in a short time, which also shows similarities to "'our" fireball cloud. We must remember to the widespread NLC sightings of the Tunguska event in 1908 happened in the middle of NLC season, when the mesopausa had the proper temperature and when the Tunguska event's meteoroid (which is said to be a comet fragment according to some studies) enetered the atmosphere it added a huge amount of water to it - and of course a huge amount of dust too. In our case now it was not the water amount that mainly counted, I think, but the dust which was created by the fireball's burnt. Stratosphere is also very dry, so the nucleation there needs a good amount of seeds which were brought there by the fireball. The dust helped the water in the stratosphere to form the cloud. The cloud spread quickly and as it contained a beforehand given amount of dust and water ice it thinned, so it disappeared from the daylight sky of Russia. The winds in the stratosphere helped this big but thin cloud to get over western Europe in 4 days - where there were clear sky and so many people could observe it. In Eastern and Central Europe the sky was completely cloudy in those days, so any earlier observation was actually impossible. Sorry for being so long with my words.
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Post by Julius on Feb 24, 2013 10:52:04 GMT
First of all I'd like to thank you all for posting the observations and sharing pics. From Hungary where I live we only had one evening without troposheric clouds, the date was 20th Feb. On this evening 3 of the Hungarian observers were looking for the possible sight of the fireball's remnants above. We only had very faint stripes on our Western sky, but still they were easily visible for the naked eye. There were no cirrus clouds present in our region. The altitude of these stripes were for sure not too high, I mean they were rather somewhere in the lower stratosphere. They became visible at the time of local sunset (actually cca. 10 minutes before it) and were still visible 40 minutes after it. They streched up to 10 degrees alt. on my sky at their best visibility. I think they resemble a bit to the SO2 clouds we could observe after the recent years' big volcanic eruptions of the Northern Hemisphere, after Kasatochi, Sarychev and Nabro. These clouds were all in the stratosphere, transported and rippled by the strong winds there (and maybe ordered by the same gravity wave process which makes the structure of NLCs or airglow). The actual observations you posted here and on SW has a good coincidence with it, but you had been much closer to the location of the greatest mass of the clouds. The fireball began its most intensive burn at the altitude of cca. 30 kms which would also make sense for its remnants being at a similar altitude. Of course this cloud also depletes a bit, so the lower stratosphere is good a place to look for it. (The blast of the fireball happened at a much lower altitude, according to the videos which showed it brightening and somewhat later the sound wave of the blast came). During the burnt of the fireball, still in the stratosphere it must have created enough nucleation seeds for the trail being so spectacular we could see on the pics and videos of it. I have seen some Russian pics of the trail taken in 3 hours after the fireball entered their atmosphere and the pics show a slow dissipation of the visible "cloud" of the trail. On the last pic it looked like a thin layer only. I have received no observation (from Russia) of any bright cloud from the evening after the fireball, neither from the morning after it. (Still have one photographer who might have some info, today I'll contact him) What my 'theory' is: the cloud you observed was not an NLC in any aspect, but rather some stratospheric cloud. Also it is cold enough in the stratosphere at winter to keep the amount of water frozen on the nucleation seeds of the fireball's remnants. The whole process is similar to a volcanic eruption's sulphuric acid cloud also in the stratosphere. We know that those volcanic clouds travel to great distances in a short time, which also shows similarities to "'our" fireball cloud. We must remember to the widespread NLC sightings of the Tunguska event in 1908 happened in the middle of NLC season, when the mesopausa had the proper temperature and when the Tunguska event's meteoroid (which is said to be a comet fragment according to some studies) enetered the atmosphere it added a huge amount of water to it - and of course a huge amount of dust too. In our case now it was not the water amount that mainly counted, I think, but the dust which was created by the fireball's burnt. Stratosphere is also very dry, so the nucleation there needs a good amount of seeds which were brought there by the fireball. The dust helped the water in the stratosphere to form the cloud. The cloud spread quickly and as it contained a beforehand given amount of dust and water ice it thinned, so it disappeared from the daylight sky of Russia. The winds in the stratosphere helped this big but thin cloud to get over western Europe in 4 days - where there were clear sky and so many people could observe it. In Eastern and Central Europe the sky was completely cloudy in those days, so any earlier observation was actually impossible. Sorry for being so long with my words. Thank you very much for your detailed post. I just added some paragraphs to make it easier to read.
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Post by tomaxe on Feb 24, 2013 13:42:05 GMT
... Could you possibly explain how one goes about calculating the height of the clouds? ... I have just oploaded my calculations in a new post on my blog (sorry most of the content on the blog is in danish!) grib-stjernerne.dk/2013/02/24/calculation-of-cloud-height/In the post you will find at short explanation and in the bottom there is link to a pdf-paper with my calculations. As I write in the post. The first calculation I did on the 19th. was quick and dirty by assuming the sun and clouds was due west, which they were not! The new calculation in the pdf-fil, takes this into account, and this results in at slightly higher altitude of the clouds. But with the uncertaities involved I think 60 km is still a good approximation.
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Post by Julius on Feb 24, 2013 15:49:27 GMT
Excellent Tom, thank you very much for the guide to the calculations. I will be back later today with som calculations based on what I observed.
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Post by stratus on Feb 24, 2013 17:37:38 GMT
Hi, on the evening of February 20th and the morning of February 21st, in Riga, Latvia I observed these noctilucent-like clouds. Here is one picture: dabasparadibufoto.files.wordpress.com/2013/01/mg_9825.jpgI can upload more if needed. Image was taken on 21st February, 5:08 am(UTC) Sunrise was at 5:34 am(UTC) Max. height above the horizon was about 25 degrees Clouds completely disappeared 5 - 10 minutes before sunrise. In the evening of Feb 21st the clouds were gone. Hope this information is useful.
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Post by Julius on Feb 24, 2013 19:35:35 GMT
Beautiful picture Ivo and excellent observation thank you for sharing.
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Post by meteoweb on Feb 24, 2013 21:20:22 GMT
Hello! Today (February 24) in the morning and evening in Moscow observed NLC www.astronomy.ru/forum/index.php/topic,2799.msg2316182.html#msg2316182 Connection with the Chelyabinsk meteorite obvious. We will investigate. Egor
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Post by Julius on Feb 24, 2013 21:53:23 GMT
That is awesome Egor, really interesting to see where the clouds will appear next.
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Post by ediacara on Feb 25, 2013 6:38:23 GMT
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Post by ediacara on Feb 25, 2013 7:25:41 GMT
Hi, on the evening of February 20th and the morning of February 21st, in Riga, Latvia I observed these noctilucent-like clouds. Here is one picture: dabasparadibufoto.files.wordpress.com/2013/01/mg_9825.jpgI can upload more if needed. Image was taken on 21st February, 5:08 am(UTC) Sunrise was at 5:34 am(UTC) Max. height above the horizon was about 25 degrees Clouds completely disappeared 5 - 10 minutes before sunrise. In the evening of Feb 21st the clouds were gone. Hope this information is useful. Ivo, thanks a lot for the excellent pic! I have found the CALIPSO satellite's LIDAR image referring your location with a stratospheric signal on 21th morning hours: www-calipso.larc.nasa.gov/data/BROWSE/production/V3-02/2013-02-21/2013-02-21_09-59-22_V3.02_4_6.pngThat yellow square is the stratospheric scattering signal at your latitude, so you might have seen that cloud!
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Post by stratus on Feb 25, 2013 8:31:02 GMT
Ediacara, thank you for the link to LIDAR image.
I will continue to watch evening an morning skies for other unusual clouds. Unfortunately - no clouds in this morning, except some tropospheric cirrus.
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Post by meteoweb on Feb 25, 2013 8:42:06 GMT
Watched this morning. The clouds were very bright, but without any significant structures. Uniform surface with seals. www.astronomy.ru/forum/index.php/topic,2799.msg2316803.html#msg2316803 Skornyayus nature of stratospheric clouds. Egor
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Post by ediacara on Feb 25, 2013 15:10:50 GMT
Egor, what time did you see the clouds today morning and what was the time of sunrise?
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