[LASS Soaring] Birds

[Nex12Go at aol.com]

NACREOUS ABUNDANCE: Veteran sky watchers in Scandinavia can hardly believe  
their eyes. At the end of the day, the sun sets as usual, the sky grows dark,  
but instead of stars, nacreous clouds appear. "We've had four displays in the  
past week alone," reports Håkon Dahle of Oslo, Norway, who caught a flock of  
birds backlit by a glowing veil of _pearly  color_ 
(http://spaceweather.com/submissions/lar
ge_image_popup.php?image_name=HAykon-Dahle-Jan25_0_1201307971.jpg)  last night: 
 
(http://spaceweather.com/submissions/large_image_popup.php?image_name=HAykon-Dahle-Jan25_0_1201307971.jpg)  
Nacreous clouds are supposed to be rare, but lately they've rolled across the 
 Arctic circle with puzzling regularity. "It's almost hard to believe," says  
Swedish photographer P-M Hedén whose _Jan.  25th photos_ 
(http://spaceweather.com/submissions/large_image_popup.php?image_name=P-M-HedAcn-Nacreous-clouds-on
e_1201299134.jpg)  nicely highlight the difference between ordinary clouds,  
scudding dark and low through the twilight, and the pearly-colored nacreous  
clouds floating airily overhead. "The clouds were _all  over the sky_ 
(http://spaceweather.com/submissions/large_image_popup.php?image_name=Morten-Ross-DSC_59
32a_1201293875.jpg)  today - from dawn til dusk," adds Morten Ross of Oslo, 
Norway.  "Incredible!" 
Also known as "Mother of Pearl" clouds, nacreous clouds are peppered with  
tiny ice crystals that blaze with iridescent color when struck by light from the 
 setting sun. It is these crystals that make nacreous clouds rare: they 
require  exceptionally low temperatures of minus 85 Celsius (-120 F) to form. 
Nacrous  clouds float 9 to 16 _miles  high_ 
(http://www.atoptics.co.uk/highsky/htrop.htm) , curling and uncurling hypnotically as they are stretched in and out 
by  atmospheric _gravity  waves_ (http://www.atoptics.co.uk/highsky/hgrav.htm) 
. 
Why the sudden abundance? No one knows, neither why the clouds  have come nor 
when they will go. Sky watchers from Scandinavia to Alaska should  remain 
alert for more in the nights ahead.



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48)
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