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Post by mesospheric on Jun 7, 2011 8:12:53 GMT
Latest temperatures for the mesosphere. Dip around 3/6 appears to match widespread NLC reports. Attachments:
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Post by Bill W on Jun 7, 2011 8:29:50 GMT
Hi, Is this data from the MST at Aberystwyth? Cheers, Bill.
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Post by markt on Jun 7, 2011 9:34:09 GMT
Cheers John! We need these temps to stay below that red line!
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Post by mesospheric on Jun 7, 2011 10:52:36 GMT
Bill: No, the data comes in from the University of Bath's 30MHz meteor radar based in Esrange, arctic Sweden. You can also find data, which is, as currently, rather slow to update and occasionally breaks down, from AURA, NASAs atmospheric research satellite, courtesy of Hugh Pumphrey, Edinburgh University here: xweb.geos.ed.ac.uk/~hcp/meso_ts/Markt: we do, although it's only a general idea of when NLC might form. The important point now is that the temperatures geneally lie below that line, whether the 5-day wave is in a warming or cooling phase.
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Post by markt on Jun 7, 2011 17:01:37 GMT
Markt: we do, although it's only a general idea of when NLC might form. The important point now is that the temperatures geneally lie below that line, whether the 5-day wave is in a warming or cooling phase. Interesting John, could you elaborate somemore of the 5 day wave warming / cooling phase please - what's the wave? what causes it etc? Thanks, Mark
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Post by mesospheric on Jun 8, 2011 10:49:43 GMT
Mark,
I'll try! I spent a whole day down in Bath going through a Ph.D.-level introduction to all this at rapid-fire pace!
The planetary waves are now believed to be (which shows you how novel and complex all this is !) natural resonances of the middle atmosphere. There are various periods, including a 2-day, 5-day and 16-day. The 2 day wave induces temperature changes too quickly to modulate NLC displays, but the 5-day wave is the 'Goldilocks' version that changes at just the right rate to bring about changes in NLC. It is a wave number 2 form. I think I recall correctly when I say the 16-day wave has only a small influence on temperatures, so is not readily detectable.
In very simple essence, the waves set-up due to the resonance alternately draw cool and then warmer air, which is how the NLC are modulated; the colder phase of course is postulated to enhance NLC due to lowering of the temperature.
The waves are very large in scale, so measurements taken in Arctic Sweden, although slightly colder than the mesosphere closer to the UK, are much as they would be if we had a radar set here. We showed that there was no time lag between the two locations, so it's a reliable means of providing data for European observers.
The correlation we found on just one season's data (and so we need many more) between cold phases of the wave and NLC enhancement (as indicated by vertical extent/altitude) was 0.47, where 1 is perfect correlation, 0 is none. This is a moderately strong relationship indicating that other factors (UV, local upwelling, etc) are also at work.
Those hexagonal shapes you get around the poles of the gas giant planets are wave number 6 planetary waves.
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Post by Bill W on Jun 8, 2011 11:56:32 GMT
Hi John, What were you reading? I'd like to have a look if its a book or a paper. The problem with correlations, like lies, d**n lies and statistics, is that it doesn't mean causation. I'd have said that 0.47 was middling (BUT I don't know what type of regression analysis was used). If you do a google of correlation and causality there is a really good example on Wiki with a group of data with the same high +0.8 correlation and they definitely don't show the the same thing. The best one is the data plot with a single outlier that takes the correlation from 1 to the 0.8 range, a single data point. It's getting longer and longer since I've even opened a maths book but I'm pretty sure it's to do with the linearity of the relationship. Your absolutley right that more observations are required! The temp plots are great, will you be doing more with Bath? The radar stuff is very interesting. I've been up to EISCAT in the mid 90's and its just fantastic what these radars show. cheers, Bill. PS First posting flagged "D**n" as a sweary, hopefully nobody is offended by the context
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Post by mesospheric on Jun 8, 2011 12:20:42 GMT
Bill,
I don't dispute what you say for a moment. I suspect there'll be a paper from the 2010 and 2011 observations after this season's over, but it depends on time and all the rest.
The 'moderately strong' description was what Prof. Mitchell used to describe the correlation, and so I think you would have to pick that argument up with him. As my post on PWs clearly indicates, I don't profess to be an atmospheric science expert.
For now, I'm content to widen my background understanding of the atmosphere (being a microbiologist by original trade) and make scientifically-reliable observations; I'd very much encourage anyone who has hitherto just observed for fun or photography to do the same.
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Post by Bill W on Jun 8, 2011 13:48:48 GMT
Hi, I have to admit that these natural sciences are always a nightmare to try and get a handle on but it always pay's to be skeptical. I like the quote from the astronomer Dave Jewitt. "Be skeptical of everything otherwise you just buy into the established paradigm"
Anyway that's enough philosophy for the time being, what I want to know is when are we going to get this barbeque summer we were promised last year!
cheers, Bill.
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Post by markt on Jun 9, 2011 19:17:35 GMT
Interesting. Sooooo, one might expect NLC to operate on a cadence of 5/10 days?
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Post by Bill W on Jun 10, 2011 7:52:50 GMT
Mmmmmmaybe....
These waves have been known about for quite some time. A few years back when we had a spell of really good weather me and Tom tried to spy when there would be good displays over these intervals. But there were nights when there were nowt.
It's interesting to look back through the archives on the NLC Observers homepage and count intervals between good displays, sometimes it fits sometimes it doesn't.
Over the years what I've noticed; entirely from personal observations; is that good displays occur at full moon. This is a great example of dodgy statistics! Are the NLC's there because the moon is full (perhaps a tidal effect?) or because the weather is good and I happen to see both the NLC and the moon at the same time? Or even, is the weather good because the moon is full? or is it just summer....?
So here is a challenge.
Keep a special eye on the sky on the night of 15/16 June and 14/15 July (the nights of full moon) and let us see what we see....
Cheers, Bill.
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Post by mesospheric on Jun 11, 2011 7:40:03 GMT
Bill > that rather confirms the imperfect correlation then! There are a number of waves, not just the 5-day. Come to think of it, I think we're going round in circles, as I've already posted on that! The moon relationship is also published data.
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Post by Bill W on Jun 11, 2011 11:17:26 GMT
Exactly and indeed it is, but it's always fun to watch out for such instances.
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Post by markt on Jun 11, 2011 16:50:59 GMT
Great thread Bill and John! Yes, whenever the weather allows I will look out on these dates!
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Post by mesospheric on Jun 13, 2011 7:48:48 GMT
Latest data just in. I need to plot the negative sightings later on - no time right now! Attachments:
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