This story about noctilucent clouds on NASA’s Science website made me think about a few things.
What I wonder is this: could noctilucent clouds be a proxy for cosmic ray interactions? While there are a lot of high energy galactic cosmic rays (GCR’s), there are GCR”s that are coming in at low energies as well. The lower the energy, the higher in the atmosphere would be their primary target area. The lower the energy, the more the earth’s magnetic field is deflecting them, redirecting then towards the magnetic poles like the protons of the solar wind (which have much lower energies).
Noctilucent clouds are not yet well understood, and given the size of the NLC ice crystals, cosmic ray interaction could be a possible trigger for their formation. As many of you know, cosmic rays leave tiny nucleation tracks, in the atmosphere. much like they do when entering a cloud chamber in a nuclear physics lab. I built one once as high school student and watched cosmic rays and other background radiation zip through.
Tracking particles and cosmic rays in a cloud chamber
As occurs in a supercooled cloud chamber (dry ice is involved) it would seem to me that cosmic ray interaction with very rarefied supercooled water vapor could be occurring in the 60-90 km altitude range. While the mechasism of a cloud chamber relies on supersaturation to leave a visbile trail, an interaction that forms a small ice crystal in the nanometer range may not need supersaturation. And, given that NLC’s form mostly at high latitudes, as aurora borealis does, there may be an interactive component of some sorts with earth’s magnetic field.
I’m also thinking NLC’s may very well be the equivalent of “dark matter in the universe” for our atmospheric interface with space and incoming solar radiation. As mentioned in the article “There is a substantial population of invisible noctilucent clouds, a population of much smaller ice crystals (< 30 nm) that don’t scatter much sunlight.” They may be small, but may have an albedo effect of some sort that is undiscovered. This is all just conjecture on my part, but I thought it would make for interesting discussion. If nothing else, NLC’s illustrate that we still don’t know how all aspects of the atmosphere work, and the portion that is closest to space is the one that is the most difficult to measure. I welcome discussion. – Anthony
UPDATE: Here is an excellent powerpoint presentation on NLC’s:
http://gwest.gats-inc.com/nlc_epo/epo_nlc_lesson.ppt
h/t to Fernando Mafili from comments
Strange Clouds at the Edge of Space
August 25, 2008: When in space, keep an eye on the window. You never know what you might see.
Last month, astronauts on board the International Space Station (ISS) witnessed a beautiful display of noctilucent or “night-shining” clouds. The station was located about 340 km over western Mongolia on July 22nd when the crew snapped this picture:
Above: Noctilucent clouds photographed by the crew of the ISS: more.
Atmospheric scientist Gary Thomas of the University of Colorado has seen thousands of noctilucent cloud (NLC) photos, and he ranks this one among the best. “It’s lovely,” he says. “And it shows just how high these clouds really are–at the very edge of space.”
He estimates the electric-blue band was 83 km above Earth’s surface, higher than 99.999% of our planet’s atmosphere. The sky at that altitude is space-black. It is the realm of meteors, high-energy auroras and decaying satellites.
What are clouds doing up there? “That’s what we’re trying to find out,” says Thomas. Read the rest of this entry »
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