I have had an email from Lon Riesberg of Laboratory for Atmospheric and Space Physics, Boulder, Colorado who operate the CIPS imager on the AIM satellite that is looking for NLCs from above. At present they have not seen any NLC in the data for this year however they have not finished processing the data yet - they hope to have this done and the images on the web site by Monday.
Thanks for that information. I just ran the AIM animation from 2007 and, from what I can see, the first NLC seems to have been recorded on May 25th (Arctic Ocean, north of Spitsbergen) and then on 27th (Arctic Ocean, north of Greenland). Activity on both days looks very weak though and it's a struggle to see it at all! A negative gap follows till June 1st, thereafter the season can be seen growing nicely. It will certainly be interesting watching the 2008 AIM/CIPS results come in.
I had a look at my calculations for the Sun Altitude at the quoted times for the NLC and get an altitude of -18 deg to -15 degrees. This would normally be considered too low for NLCs. This makes it more mysterious.
I don't think we may get much help from AIM - it flew just West of Ireland at about 01:15 so may have been too early to see any NLCs. This time is only an estimate using Heavens Above - if they have altered the orbit predicting backwards using the current TLE's will give the wrong result.
We should get data from ARM tomorrow though bear in mind all the Petals are not taken at the same time - I will have to check the orbital period but I would guess it's about 90 min.
- 6 to -16 degrees is the typical solar height for NLCs, the conditions were sufficent enough for NLC illumination. Has anybody been watching for more?. I haven't had a decent clear night here since during the prime evening and morning windows. Since it will soon be mid May there should/could be more low level diffuse displays visible given the current activity. Be on the look out!
Olaf, thanks for the comments, at least this will generate some interesting discussion. Remember that visual observations are a large part of NLC science, this has always been the case and will continue to do so. Another point to keep in mind is that very experienced visual observers who train their eye on the sky on a nightly bases for years, particularly at the dusk and dawn regions, do not see optical illusions. Optical illusions/errors only occur with new observers. I wasn't going to continue with this thread any further however I feel it is important to make new visitors aware that further NLC (or suspect NLC) observations are encouraged.
In the mean time I think the time could be spent more productively by undertaking further observation of the twilight regions.
The very early sightings of an NLC on May 4/5 by John McConnell and Martin McKenna prompts me to ask what is the all-time record earliest NLC seen from Europe? Mark Zalcik from the CAN-AM network tells me that there was a definite sighting on May 5/6, 1996, 0800-1015 UT, at Anchorage, AK (61.1N), but didn't say who the observer was. Also I should comment that if the solar depression angle of the recent NLC was greater than 16 degrees, this would place the observation as doubtful, would it not? Unless the cloud were considerably higher than normal. I calculate that roughly every degree of solar depression angle will change the shadow height by 4.4 km.
- 6 to -16 degrees is the typical solar height for NLCs.
If we have any computer whizzes here what would be pretty good is a little computer program thingy-me-bob that for a given geographical location and date would generate an evening and morning time when the sun is between 6 and 16 degrees below the horizon. Kind of a 'NLC visibilty calculator' - Just a thought...
*edit* Or as an after thought if there's anything out there that already does this then there's no point in re-inventing the wheel - anybody know anything on this one?
The earliest NLC observation on record as far as I'm aware occured on May 1st 1850 from Armagh Observatory, N. Ireland by the then third director Thomas Romney Robinson who noted 'strange luminous clouds in NW, not auroral'. This predates the observation by Thomas W. Backhouse in 1885, two years after the Krakatoa eruption. Not many people are aware of Robinson's observation. This fact was discovered by Dr. John Butler, astronomer at Armagh Observatory
Thought I would add this observation which was sent to me recently from Austin Taylor...
''I saw your request for other sightings of NLC on 5 May. I saw them on the morning of 6 May from my home in Shetland. It was about 0330 BST. They were quite different to the ones you saw, being much higher in altitude, almost overhead and more fluffy and billowing. They were fairly feint, but quite distinct, and I pondered a while if I could get a worthwhile photo but decided against because I had just come in from a very late folk festival night so was tired and probably would have struggled a little to get a decent photo! Had they been much brighter, or there had been greater contrast with the fairly bright sky I would have tried but the combination of factors and that I was to be at work the next morning dissuaded me. This is the time to look for them in Shetland because it's simply too bright in June and July''...Austin Taylor.
Cheers for that Bill. I had tried to 'Wiki' it but got links that went to nowhere or they were naff.
Cartes Du Ciel downloaded now - surprised me when I ran the the twilight times for my location what the actual times were! Being the sort of chap I am i've just sat and ran them for my forthcoming holidays for the next couple of months too - i'm easily amused
Hi, It is a GREAT pity that your contact in Shetland didn't take that picture! It may well have silenced the less pleasant critics and enlightened us sceptics however...
What the description reminded me of was a possible display I saw from Durness the night before the annular eclipse a few years back. This too was faint and diffuse and overhead. There is a picture on the main NLC website in the gallery bit. To this day I'm not sure if I can convince myself if it was a genuine nlc or faintly illuminated cirrus.
It'll be interesting to see if anything comes from the AIM data. All good stuff! cheers, Bill.
I have just had a look at the AIM CIPS imager daily daisy's and there is no sign of any NLC anywhere on any of them
Bear in mind that as my earlier post the Satellite went over at around 01:20 though I am waiting to download the strip images to check the time.
It's not clear to me what the spacecraft NLC Sun geometry has to be to allow the clouds to be imaged - I assume they have to be in Sunlight though the imager is working in the UV. The Satellite will be in daylight earlier as it is higher.