Discrepancy between observations at end of May and AIM

[johnm]

There have been a couple of observations of NLC from the Denmark & Northern Germany reported here and on Spaceweather.com.

Looking at the prelimiary AIM observations for both the 31st May & 1st June 2014 on spaceweather.com there is little sign of NLC activity and what there is is around 80 degrees north.

There might be a different view from AIM when the final images are published in a few days but for the moment can anyone explain the discrepancy ?

Good Observing

JohnM

[Bill W]

Hi,

A good point and a good question!

The AIM satellite imaging systems is looking at a very short wavelength. This is specifically designed for imaging Polar Mesospheric Clouds (PMC). Noctilucent clouds are related to PMC.

On the AIM website there is a data sheet which states that PMC and NLC are "one in the same". If you read any of the more scientific journals there are others that disagree with that! Due to formation location and specific timing they may be concurrent but not necessarily exactly the same thing.

Anyway you've discovered for yourself that the satellite is seeing different stuff. There used to be info about the imaging system but I can't find it. I'm sure it is working around 200nm so that it "see's" particles of a particular size. Viz it's seeing the stuff at high latitude but not the stuff at lower latitude.

The other issue is more simple and that is orbital timing. The satellite is only over the region for a relatively short period. Other activity could come and go between orbits. That's where many eye's always helps!

It's a good guide but I wouldn't rely on it to provide definite indication of NLC per se. That's the way I read how the thing works but I could be wrong!

Cheers,
Bill.

[johnm]

Thanks for the reply Bill,

I found a link to a thesis on 'Polar Mesospheric Clouds: A Satellite and Ground-Based Comparison' at link to thesis

This has some comparisons of AIM results with visual observations. I have not read it yet but it looks as though at least parts of it may be relavant from the abstract.

I found another more general PMC site but will put a seperate post on this in a more appropriate place.

I will link both to the NLC pages on my website at link to John Murrell's web site

Regards

[whamburg]

Moin moin,

AIM(CIPS) doesn't "see" all mesopheric clouds. It needs sunlight and a specific angle range between sunlight and the line of view to detect PMC. So it's possible that CIPS can't detect clouds especially for latitudes below 70°. Is the daily flyover in darkness or twilight(not unusual for lower latitudes) the data will be not captured or not proccessed.
For more details read: aim.hamptonu.edu/docs/AIM2013SeniorReviewReferences/Lumpe_et_al_ATP3419.pdf
The "daily daisy" aka CIPS Level 3A Data is available with a three or four day delay. So it can't be used for NLC forecast.

BR,
wolfgang