Expert: Paul Soderman - 1/24/2003

Question
Hi Paul.
I guess you are familiar with boundary layers, and here's my question: How can the shape of cumulus clouds tell us the direction of flow of air, using boundary layer ideas? Thanks a lot.

Answer
Hi Feras

I am familiar with boundary layers, but most clouds are out of the earth's wind boundary layer, which is usually a few hundred feet thick.  You may be thinking of the interaction of clouds with shear layers that can be found in the jet stream or top of the stratosphere, for example.  When a cloud rises into the shear layer, the top of the cloud will flow windward and you can thereby see the wind direction at that elevation.  Below the shear layer, I don't think the shape of the cloud would be as important as its motion for indicating wind direction.  An experienced sailor might be more able to understand cloud shapes than I am.

Hope this helps.

Paul

p.s.  I should have said bottom of the stratosphere; i.e., at the interface of the troposphere, which touches the ground, and the stratosphere above.