Shot this northerly sunset a couple of days ago in Spitsbergen...anybody has
a name for the peculiar clouds (there is a second one in the background)???
http://www.thijsheslenfeld.com/frame.php?itemId=63452

Thanks a lot,

T.Heslenfeld
www.thijsheslenfeld.com
kees-at-thijsheslenfeld...dot...com

On 4 Sep, 15:59, "T.Heslenfeld" officeatoostwestthijsbestdotnl
wrote:
Shot this northerly sunset a couple of days ago in Spitsbergen...anybody has
a name for the peculiar clouds (there is a second one in the background)???http://www.thijsheslenfeld.com/frame.php?itemId=63452

Thanks a lot,

This is a spectacularly photographed example of a fallstreak hole -
the Americans call them punch-hole clouds. They are caused by
glaciation of the water droplets in the layer of altocumulus, and the
"streak" is falling ice crystals or, technically, virga.

I notice a second one in the photo at a distance.

Martin



T.Heslenfeldwww.thijsheslenfeld.com
kees-at-thijsheslenfeld...dot...com

The picture shows an excellent example of virga or fall streaks. This is
precipitation, usually in the form of ice crystals or snow. In this case the
two examples are falling from a layer of stratiform cloud, and in the closer
example it can be seen that thinning and breaks are occurring in the area of
cloud surrounding the virga. The mechanism known as the Bergeron-Findeisen
process is responsible. For this process the cloud must be composed of
super-cooled water droplets at a temperature well below zero C. Some trigger
mechanism, sometimes caused by the passage of an aircraft through the cloud
layer, causes some of the droplets to freeze into ice crystals. As the
saturation vapour pressure over water is greater than that over ice, the ice
crystals grow rapidly at the expense of the water droplets. This is because
the relative humidity with respect to water must be near 100 % in the cloud,
and thus greater than 100 % with respect to ice. As the ice crystals grow
rapidly they tend to lower the relative humidity towards 100 % for ice, thus
reducing it below 100 % for water drops, and causing the water cloud to thin
at the same time as the ice crystals precipitate out. You do not say what
date the photo was taken, but suitable days in August, after looking at the
upper air soundings for Ny-Alesund, would be 6th 10000 ft, 21st 5000ft, 25th
8000ft, and 30th 8000ft. It may have been possible on other days, as there
is only one sounding per day normally.

-
Bernard Burton
Wokingham, Berkshire, UK.

Satellite images at:
www.woksat.info/wwp.html
or
www.btinternet.com/~wokingham.weather/wwp.html
"T.Heslenfeld" officeatoostwestthijsbestdotnl wrote in message
...
Shot this northerly sunset a couple of days ago in Spitsbergen...anybody
has
a name for the peculiar clouds (there is a second one in the
background)???
http://www.thijsheslenfeld.com/frame.php?itemId=63452

Thanks a lot,

T.Heslenfeld
www.thijsheslenfeld.com
kees-at-thijsheslenfeld...dot...com