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Post by menno on Jun 20, 2007 22:52:06 GMT
Hello, Although I live in The Netherlands and have seen NLC before, I wonder to what southern latitude NLCs' can be seen?
A few days' ago they were reported in Vienna and Budapest. I often visit Romania in summer, can they be seen there at 46N ?
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Post by Bill W on Jun 21, 2007 13:47:03 GMT
The short answer is yes they can be seen. For the best chances you'll need to determine what times the solar depression angle is between 6 to 16 degrees and watch during these periods. At lower latitudes the sun dips out of this range around 00 00 hours so in theory you'll have two spells, one before midnight (to the west) and one after (to the east) but it's always worth checking at all times! regards, Bill.
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Post by martinastro on Jun 21, 2007 16:47:17 GMT
I second what Brian said. There has been a suggestion that NLCs are being recorded at lower and lower latitudes during recent years and I was wondering if Tom or anyone else would have any observational evidence to support this? If this is the case then I am assuming this would be a sign of changes in the Mesosphere or global warming? * Brian I like your quote under your avatar! I live by that rule myself.
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Post by tmcewan on Jun 24, 2007 12:57:36 GMT
I second what Brian said. There has been a suggestion that NLCs are being recorded at lower and lower latitudes during recent years and I was wondering if Tom or anyone else would have any observational evidence to support this? If this is the case then I am assuming this would be a sign of changes in the Mesosphere or global warming? If you browse through the archives on nlcnet.co.uk you'll come across several reports of southerly (below 50N) sightings; the ones that spring to mind from last year are Venice, Italy (Lat 44.4) and Alma-Ata , Kazakhstan (43.2). This year we have already had reports from Alma-Ata and from Oregon (Lat 43). The lowest confirmed sighting I know of was from Colorado (Lat 39.53') on 1999, June 22-23. Whether this is a new feature of NLC behaviour, or, something that just hasn't been noticed before is an intriguing question. There's also some evidence to suggest that the NLC seasons are becoming longer - again, is this real, or, the result of more efficient and dedicated observation? These are questions we can all help to answer by continuing to make accurate and detailed NLC observations.
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Post by febo1966 on Jun 24, 2007 18:29:19 GMT
Hello, this morning I have seen NLC from Verghereto (Italy), at a latitude 43.8. It's my lowest latitude observation. Bye
Fabrizio Melandri
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Post by tmcewan on Jun 24, 2007 20:17:06 GMT
Hi Febrizio,
Good to hear that you've observed another NLC in Italy. Could you possibly send a report via the website?
Welcome to the forum and best of luck with the rest of the season...
Tom
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Post by febo1966 on Jun 24, 2007 23:21:43 GMT
Hi Tom, I will send a report in 2-3 days: time to develop film and see the photos; so I can send more accurately data.
Fabrizio
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Post by tmcewan on Jun 25, 2007 8:52:14 GMT
Hi Fabrizio,
Great! Looking forward to it...
Tom
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Post by alcoor on Jun 25, 2007 9:25:40 GMT
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Post by Bill W on Jul 3, 2007 11:18:57 GMT
If this is the case then I am assuming this would be a sign of changes in the Mesosphere or global warming? There are a lot of myths surrounding NLC. An excellent non technical review is "Are NLC truly a miners canary for global change." by Ulf Von Zahn in EOS, Transactions of the American Geophysical Union, Vol 84, number 28, 15 July 2003. As organiser I gave a presentation at the Scottish Astronomers Group special meeting on NLC last August which looked at recent trends and depending on how exactly the numbers are crunched I could show that NLC are actually declining!, a case of lies, d**ned lies and statistics... It is the "brightness" of the NLC which is the most interesting thing (and possibly the most difficult thing to quantify.) This could be in response to more condensation nuclei being present or it could be in response to more available water vapour for condensation (or a combination of both) causing more (and possibly larger) ice crystals to form. Whether these are anthropogenic in source is a tricky question... Regards, Bill.
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Post by martinastro on Jul 4, 2007 15:47:23 GMT
Very interesting Bill. Would love to learn more about this. One question though....do the records of visual NLC observations go back enough to validate whether the displays are increasing or reducing?
Are there any resources I can read to learn more?
Thanks
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Post by markt on Jul 4, 2007 15:55:37 GMT
It is the "brightness" of the NLC which is the most interesting thing (and possibly the most difficult thing to quantify.) There's a wealth of experience in terms of the members on this forum, have people here noticed NLC's being brighter in recent years, or maybe on the longer scale in terms of decades? This years NLC's seem to be brighter to me than the past couple of seasons i've been paying attention to - or am I just imagining it
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Post by martinastro on Jul 4, 2007 17:40:14 GMT
I reckon they have been getting brighter since I began observing NLC however I think 2006 would be a difficult season to beat...at least from what I have seen from here this season however other locations seem to be getting rich displays.
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Post by Bill W on Jul 5, 2007 8:29:46 GMT
Very interesting Bill. Would love to learn more about this. One question though....do the records of visual NLC observations go back enough to validate whether the displays are increasing or reducing? Are there any resources I can read to learn more? Thanks I've put two papers on my website, the EOS review and a more detailed paper. Both of these have extensive references which you can investigate further. There are LOTS of sites which give nothing more than the usual introduction (my own included!). To find out more then the best resource is the internet in terms of sourcing research papers and a university library where you should be able to find them. Regarding the second paper if you look at page three there is a detailed graph of NLC observations. As more and more observations have been reported the numbers of course slope up. This has been reported in some cases of NLC increasing. (I get the feeling that a few years ago this was almost being preached as gospel and hence the EOS article was an attempt to rectify this) They MAY be, but equally this may be due to a much greater awareness and more people seeing and reporting them. Now that lots of observers are getting into the habit of looking for NLC maybe in the future it will be clear what the true situation is. So to answer your question, at the moment, I don't think anybody really knows! cheers, Bill.
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Post by olaf3sky on Jul 5, 2007 19:40:52 GMT
They MAY be, but equally this may be due to a much greater awareness and more people seeing and reporting them. Now that lots of observers are getting into the habit of looking for NLC maybe in the future it will be clear what the true situation is. So to answer your question, at the moment, I don't think anybody really knows! cheers, Bill. Hi Bill, in my opinion this is very important to mention! Regards, Olaf
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