Video: Solar rain
THE sun's million-degree outer atmosphere is the last place you would expect to find rain, yet a form of it does occur there. The stuff could help explain why the sun's outer atmosphere, or corona, is much hotter than closer in.
Coronal rain is made of dense knots thousands of kilometres across consisting of relatively cold gas, at tens or hundreds of thousands of degrees C, which pours down towards the sun's visible surface from the outer atmosphere at speeds exceeding 100 kilometres per second. "There's just this constant rain of these blobs that seem to be coming down from high up," says Judy Karpen of NASA's Goddard Space Flight Center in Greenbelt, Maryland.
Now simulations seem to show that the coronal rain is a result of the process that makes the corona so hot. Two theories have previously been put forward to explain the anomaly. One suggests the corona is heated via small explosions called nanoflares lower in the atmosphere. These would push gas up into the corona, where it radiates away its energy. The other suggests the heat energy is deposited by magnetic waves rippling through the corona.
When Patrick Antolin and Kazunari Shibata of Kyoto University, Japan, simulated the two processes, they found gas heated from below by nanoflares could cool and condense higher up to make the rain, whereas the magnetic waves kept the high-altitude gas too hot to condense.
"It's a little bit like raindrops condensing," says Daniel Müller, a European Space Agency scientist based at the NASA Goddard Space Flight Center. The gas rises "like steam evaporating from a boiling pot of water,", he says. "Then it cools down and when it gets really dense it forms these blob- like features."
Journal reference: www.arxiv.org/abs/0910.2383
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Outstanding Headline
Thu Oct 22 00:37:12 BST 2009 by David Nagel
http://campustechnology.com
That's pretty much all I wanted to say. The story's interesting, but the headline is great. If only you would have added "in the membrane" at the end....
The corona could, albeit tenuously, be described as the Sun's 'membrane'...
I thought David was meaning that the title sound like some sort or rhyme or lymeric.
Sun's rain
could explain
why corona heat is insane
once upon a time
in a membrane...
perhaps, or perhaps he was referring to the lyrics 'insane in the membrane' by cyprus hill. :P
Maybe it wasn't Purple Rain, it was Solar Rain
The high temp (1mil. deg) of Sol's corona above the lower (6000K) of the surface seems illogical; but Earth also has a region of much hotter gasses up high in our atmosphere ( the thermosphere).
The issue here above Earth is that the temp. is a measure of the speed of the atoms bumping into each other, which is much higher in an emptier area ( effectively a vacuum)- so each atom/ion can have a higher energy, but there are far fewer of them, so the overall energy per volume (heat) actually DOES reduce as we ascend from Earths surface.
The "rain" recondensation aspect is pretty neat, tho.
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