(meteorobs) CCNet on meteors / NLC

[Bruce McCurdy]

    Thanks to Robert and Rainer for an interesting thread. Here in Edmonton, 
Canada (~54° N., 114° W.) we are exceptionally well-situated to observe the 
noctilucent clouds, in fact the first sighting in these parts of the new NLC 
season was reported last night. I understand there are physical factors 
related to the geography of our region, and the fact we are nowhere near any 
sort of a coastline is some sort of advantage compared to cities near our 
latitude in Europe. (Don't quote me or my imperfect memory.) I typically 
observe 10 or more NLC displays in a summer. Might as well, since there are 
no meteors this time of year ... and no astronomical darkness, for that 
matter.

    NLCs are subtle-but-beautiful ripples and whorls of electric blue, 
bathed in sunlight at an altitude of some 80 km, hugging the horizon 
somewhere below Capella (which for us is comfortably circumpolar). Displays 
develop slowly but are very dynamic at time-lapse photography scales. 
Indeed, NLCs rank more or less equally with aurorae, rainbows, 
sunrises/sets, electrical storms, and (gasp) meteors as my favourite 
atmospheric phenomena. All are timeless, thus never grow "old".

    As to Prof von Zahn's assertions, I posed the question to Mark Zalcik, a 
local expert on NLCs who has been the hub of the NLC Can/Am network for 
about 20 years. Mark stated:

*****
> I somewhat agree with von Zahn.  We've been watching in North America for
close to 20 years and there has not been a noticeable increase in NLC over
that time, though the last couple of years may be the beginning of some kind 
of trend, with 54 active nights in 2003 and 50 last year [compared to an 
average of 35-40].  I have been keeping close track of statistics from our 
sites that observe every hour, every night through the whole season, and 
taking these data into consideration, there has not been much of a trend. 
And now we only have a handful of such sites participating, which doesn't 
help prove anything either way.
*****

    For those of you too far south to experience them firsthand, a fairly 
typical display of NLCs imaged by fellow Edmontonian Kevin Jeske can be seen 
at http://www.nlcnet.co.uk/nlcpix23.html . (Notice too the mild aurora!) And 
go cry in your dark skies that you can't experience these delights for 
yourself.  :)

    Bruce

*****
----- Original Message ----- 
From: "RainerArlt" <rarlt at aip.de>
To: "Global Meteor Observing Forum" <meteorobs at meteorobs.org>
Sent: Wednesday, May 25, 2005 1:54 AM
Subject: Re: (meteorobs) CCNet on meteors


>
>> SCIENTISTS USE METEORS TO INVESTIGATE CLIMATE CHANGE
>> ----------------------------------------------------
>
> Thanks for forwarding this very interesting article.
> One comments though:
>
>> The mesosphere has been called the miner's canary for climate change;
>> meaning that it is very sensitive and the changes there may be larger
>> than in any other part of the atmosphere. Evidence of these changes
>> comes from sightings of noctilucent clouds, very unusual clouds seen
>> only in polar regions and known to be in the mesosphere.
>
> Visually, these clouds are seen between 45 deg and 60 deg
> northern latitude. They are NOT SEEN above 60 deg because
> it does not get dark enough during the summer, and only
> during the summer, the temperature of the mesosphere
> drops to low enough temperatures. Noctilucent clouds can
> be detected at higher latitudes by other means - the
> text was a bit misleading. I don't think we live in a
> polar region, and we see them every summer (Berlin) ;-)
>
> There has been a long discussion about whether the number
> of NLC changes over decades. In a talk on our March meeting
> of the German meteor grous, Prof Ulf von Zahn gave a talk on
> that topic and came to the conclusion that there is no
> statistically profound evidence for a change in NLC
> occurrence rate. I think the period covered was ~30-40 years.
> Prof von Zahn was the director of the Institute of Atmospheric
> Physics (http://www.iap-kborn.de/index_e.htm), Germany. They
> have conducted mesosphere observations by radar and LIDAR
> (laser beam element detection and ranging) for ~10 years now.
>
>
> Rainer
>
>
> -- 
> Rainer Arlt  --  Astrophysikalisches Institut Potsdam -- www.aip.de
> Visual Commission - International Meteor Organization -- www.imo.net
> rarlt at aip.de --  phone: +49-331-7499-354  --  fax: +49-331-7499-526
>
> ---
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