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NASA Snaps Mysterious "Night-Shining" Clouds
coondoggie writes to tell us that NASA has captured some pretty impressive images of the Alluring noctilucent (or "night-shining") clouds. These clouds are made up of ice crystals and dust and are formed at high altitudes near the poles. "Very little is known about how these clouds form over the poles, why they are being seen more frequently and at lower latitudes than ever before, or why they have been growing brighter. AIM will observe two complete cloud seasons over both poles, documenting an entire life cycle of the shiny clouds for the first time. 'It is clear that these clouds are changing, a sign that a part of our atmosphere is changing and we do not understand how, why or what it means,' stated AIM principal investigator James Russell III of Hampton University, Hampton, Va. 'These observations suggest a connection with global change in the lower atmosphere and could represent an early warning that our Earth environment is being changed.'"
http://www.spaceweather.com/nlcs/gallery2007_page9.htm has a Noctilucent Cloud gallery. I haven't seen them yet myself, but it'll be interesting to see if AIM manages to find an explanation for them. It's an intriguing mystery!
Murphey's fighting Occam, and we're in the stands.
One theory trying to explain these clouds is the X-ray activity of the sun. The sun is a highly variable star when it comes to X-rays. During its 11-year cycle, the X-ray flux emitted by the sun varies by a factor of 15, with ferocious bursts. We are at a solar minimum, so we see few sun spots and the X-ray activity is also lower on average.
I found an article that is short and readable explaining the link between solar cycles and X-rays: http://solar.physics.montana.edu/nuggets/2000/000407/000407.html. Note that the X-ray activity can vary hugely from the current solar minimum to, say, the 2000-2001 solar max.
The problem is that we don't have that much data on it yet. We need to accumulate several cycles worth of observations before we can answer these questions:
* When does the sun emit X-rays? Is it linked to sun spots?
* What do solar X-rays do to the upper atmosphere?
The X-rays are absorbed by the ionosphere (fortunately for life forms), and this energy transfer is not well known. During each solar minimum, less X-rays arrive in the upper atmosphere, which therefore should cool down. Is it the reason why we see these noctilucent clouds? If so, they should start disappearing in a couple of years, when sun spots return.
This is a very interesting keyhole on a yet unknown mechanism. I hope we'll see updates on the subject.
Fantasy: http://ferrisfantasy.blogspot.com/
I've seen these several times over the North Atlantic in the summer.
If you're not paying attention, your first impression is that they look like cirrus clouds viewed from the ground, only much more beautiful.
It's when you remember that you're already 30+ thousand feet up, and that these look like cirrus do when you're on the ground, that you realize how high they are. (That's plain English for 'mesosphere.')
Like satellites, you can see them when your sky is dark but they are catching sunlight due to their altitude.
Right up there with northern lights as a visual treat.
Never shake hands with a man you meet in a fertility clinic.