(As)
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Height of base: |
Between 2000 and
6000 m (6500 - 18000 ft) (mid-level clouds) |
|
|
Description: |
Featureless
grayish-blue cloud layer, occasionally fibrous Extended over
large areas Often reveal
position of sun in coarse image (like trough ground glass) Can cause white
or colored corona “the boring
cloud” |
|
|
Occurrence: |
World-wide;
common in midlatitudes |
|
|
Made of: |
Supercooled water
droplets and ice crystals |
|
|
Precipitation: |
None; rarely
light rain or snow |
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|
Formation: |
Follows
Ac in approach of warm front Forming
from thickening and lowering cirrostratus |
|
|
Varieties: |
Opacus,
translucidus, undulatus, duplicatus, radiatus |
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|
How to
distinguish from … |
Cirrostratus (Cs) |
Cs produces
haloes, As does not; but both can produce coronae Sun through Cs
can produce shadow, As does not |
|
Stratus (St) |
St is lower,
often some features can be distinguished on its base; As is completely
featureless |
|
|
Nimbostratus (Nb) |
Darker; produces
heavier precipitation |
|
|
Altostratus translucidus in upper Part of image (Morris, October 2007) |
Altostratus opacus (Morris, October 2007) |
Altostratus and altocumulus, Morris, April 24, 2008 |
|
Altostratus translucidus layer and
cumulus fractus Morris, March 28, 2008 |
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Last
modified: 5/16/2008
Maintained
by Sylke Boyd