Are Noctilucent Cloulds More Prelevant During Sunspot Minima

[frogesque]

Consider the recent beautifull displays and this photo taken on July 11th. 2005 (Milnathort, Kinross). At the time I was hoping to catch a glimpse of aurora (unusual during summer months because of the shot period of darkness) since an Earth directed coronal mass ejection (CME) was due to arrive.

This is another absolutely stunning display that ended with crepuscular rays showing through the pre dawn sky. (I've forgotten when it was taken but it was a few years ago, if I can find out I'll let you know).

NLCs are fairly common at this lat. during the summer months and whilst I can't deny the rececent displays have been great they aren't that rare.

A few theories exist as to why they seem to be more prelevant at the moment and these range from high level polution from jet and rocket exhaust, sunspot activity (or lack of it) to them being just a normal part of Earth's fascinating variation.

So, What are the leading theories of board members? Are more folk looking therefore we see and hear more reports or are they a portent of impending doom?

Be creative, (but polite as always!)

[LadyPakal]

http://www.newscientist.com/article/dn1723...-this-year.html

'Although the average number of noctilucent clouds has been increasing in recent decades, their abundance also seems to rise and fall with the sun's 11-year cycle of activity. The clouds thrive when the sun is quiet and spews less ultraviolet radiation, which can destroy water needed to form the clouds and can keep temperatures too high for ice particles to form.'

[kar999]

An interesting thread topic Frog, thanks for opening up the discussion.

Your "grass" theory may have some credance, as before taking an interst in Aurora, I would have probably just put late evening Noctilucent clouds down a bright twilight summer sky. I doubt if I would have given them more than a second glance. I'd never have been up at 3am to see the morning ones, unless rolling in from a late night party!

For much the same reason, I'd never knowing seen a Sundog before but I see them all the time now and you know the signs when the conditions are right for them to form and can look out for them.

It's just a shame Aurora are less common at this latitude but it dosnt always need a solar max to give us a display. Some of the biggest CME's have been near minima.

Edited June 20, 2009 by kar999

[frogesque]

LadyP:

That makes sense on one level. However, during years of high sun activity the Earth's upper atmosphere is puffed up (technical term ) considerably higher so it should make for higher NLCs that could be seen further south than than the 'normal' 50 -60 deg lat. band.

Another aspect that might have to be considered is whether they are related in any way to upper atmosphere containing sulphur compounds from volcanic activity (especially those in the Arctic such as Alaska's Kasatochi that erupted in late August 2008 and produced the weird sunsets around that time)

At the moment I still lean towards the 'grass' theory but I really don't know the answer

I'm going away for a few days but I'll try to keep up if t'other 'arf will let me near a 'puter

Edited June 20, 2009 by frogesque

[Phil UK]

Even at 52º latitude where I am, I've seen NLC's for 3 consecutive nights in a row and as said previously , I've seen more in the past three nights or so than I have in the past ten years. I think, and doing some research since this thread was posted, sunspot minima does have a very profound effect as regarding atmospheric activity. In this case the Mesosphere where NLC's sit around 50,000ft above the Earth.

But these have recently been reported from England/Europe, even as low as Virginia in the US. Make the most of if you can guys and gals as by mid July, it's probably all over for another year. :lol:

Phil.