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Name: Timothy
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Question:
We were watching a high peak in Alps on a clear, bright day. The sun shining on the snowy peak seemed to be creating clouds, which would gather around the peak, then float away while still holding their shape. It was not steam or snow and there were no other clouds in the sky. This went on for over an hour. Can actual clouds be formed this way and if so, is there a name for this phenomenon?


Replies:
Hi Tim

"Sun shining on snow creating clouds"
Could be the process of "Sublimation"
http://en.wikipedia.org/wiki/Sublimation_(chemistry)
That is where solids, such as ice, directly pass to the gaseous state.

or it could just be melt water being evaporated in the direct rays of the Sun.

Clouds are visible water vapor. (Humidity is invisible water vapor) So the clouds you saw were water vapor rising from the snow field.

Is there a name for this cloud formation technique? My meteorological training comes from Navy flight training And I have not heard of a name for this cloud formation technique. Maybe a professional meteorologist can ferret a name from a text book somewhere. I am tempted to add that the formation of fog is somewhat similar to this process Provided the water vapor comes from the ground and does not come from the air.

But I imagine this is a quite common process.

Sincere regards,

Mike Stewart


Timothy,

The mountain peak apparently acted as an obstruction to air flow, causing air to be forced upwards at the top of the mountain. As air is lifted it cools, and, if there is sufficient water vapor, it will condense and form a cloud.

Sublimation of snow (direct ice to water phase transition) to water vapor by the bright sunshine, combined with lifting of the air, producing condensation and clouds, appears to be the mechanism for what you saw.

Since you said that the clouds formed "around" the peak, then floated away while holding their shape, I must assume that periodically the wind speed increased enough to blow the clouds away.

What you saw was different from a banner cloud produced by a mountain peak, as those form in the lee of the peak in relatively high wind speeds. What you observed was apparently produced during mostly low wind speed conditions.

David R. Cook
Meteorologist
Climate Research Section
Environmental Science Division
Argonne National Laboratory


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