Just noticed that the AIM results for the first 4 days of June are available. Looking at the daisy images there may have been minor activity on May 31st, with more obvious traces on June 1st. This gradually strengthens through to the 4th. Compared to last year, when the first traces were detected on May 25th, the 2008 season seems to have started late.
Activity is certainly start to increase compared to when you look back a month or so over the data. Bit of luck all those NLCs floating over northern Canada will be forming over northern Europe too before long...
I think you have to treat the AIM NLCs with caution as the AIM satellite has an orbital period of around 90 minutes thus each pair of petals in the daisy are taken around 90 minutes later. As a result the pass over the UK may not be at the time that the NLC are visible from the ground either they may not be there or it may not be illuminated.
You can see the time that AIM was over the UK ( or wherever you are observing from) can be found from the 'Heavens Above' web site at www.heavens-above.com/ having selected your location use 'Select a satellite from the Database' then enter AIM into the Satellite name box - AIM is the only one that comes up. Then pick the 'Passes (all)' option which will show the times of the passes on a particular date.
From the table click on the appropriate date and time and this will show you a map of the pass.
I quite agree with the way they allow us a good overview - the coverage near the poles where the stripes converge is very good.
Looking at Heavens above there seem to be two 'Night' passes and one at mid-day - at least for the UK at present. I presume the Satellite orbit is set to try to maximise the night time passes to get the best results.
Hello, This is one of those issues that can cause a lot of confusion if nomenclature is mis-used. (As a brief aside the AIM website is one of those places where the expression "electric blue" has come from!) Anyway it must be remembered that although the term NLC is used extensively throughout the AIM website what the mission is examining is Polar Mesospheric Clouds. NLC are related to PMC and represent a lower edge to PMC. However caution must be exercised when making and out and out comparison with AIM mission data and visual NLC. The AIM mission which is working at 265nm (top end of the UV-C region) specifically for reflection/scattering from a particular range of particle sizes. It is a good guide but it would be unwise to rely on it for direct comparisons. For example if the AIM satellite isn't showing anything then there are probably no NLC because there are no particles at all to nucleate, grow, fall, grow some more, fall some more, grow big enough to see and then maybe evaporate or get bunched up by gravity waves etc, etc, etc. BUT if the AIM satellite is showing a lot of activity it doesn't necessarily mean that there will be NLC either because of what the satellite is instrumented for. It's only if the growing process etc continues that we'll have particles big enough to reflect/scatter visible light giving us NLC that we can go out and see. There are also orbital geometry and solar illumination issues. This can be seen on the groovy video on the AIM site. There are peak times through July where there doesn't seem to be anything over the UK yet there were good displays. This probably applies to everywhere else as a quick look at the main web site shows NLC on just about every night for July 2007! Even considering the fact that a display lowish on the horizon will still be of the order of 1000km to the observers north it's still a bit short of the AIM data graphic project onto the Earth. I could be wrong...! cheers, Bill.
Hi, Pretty much, I don't know for sure but looking at the pictures it's probably from one, say north bound, node crossing to the next. You've probably seen it too, that NLC can come and go in the time it takes for the sat to orbit. Because of the differences in the physical properties of the PMC and NLC eye's on the ground are still a useful tool (mind you the eye's probably work better if they are in ones head!) cheers, Bill.