Physics Photo of the Week

Animated Cloud Wave

Large file - please be patient...Notice in the animation that the dark wave cloud is forming at the top of the image.  Air is rising and condensing as a cloud when it reaches the specific height where the dew point is reached.  The cloud holds its shape as it propagates toward the Great Craggy Mountains.  It is believed that the clouds are dynamic - undergoing convection at the same time as they are propagating down wind.  If so, these wave clouds are showing Kelvin-Helmholtz waves due to different air layers travelling at different speeds - somewhat like water waves caused by wind.  Here the surface air is relatively calm, while the clouds are moving away from the camera.  The dark parallel clouds are the bottom of the wave crests that form either within the thick layer of clouds or above the cloud layer. 

The picture at the right is an example of a Kelvin-Helmholtz wave cloud.  This wave cloud was published by Mark Taylor on Earth Science Picture of the Day on January 8, 2007.  The sideways views of the Kelvin-Helmholtz wave clouds are much more impressive, but I have never seen any to animate.  Any one with a digital camera and tripod can make animated cloud pictures.  If anybody can photograph an animated sequence of the Kelvin-Helmholtz waves please send them to me.

The animated image above was made by taking a photograph manually once every 10 sec.  The 3 min 20 sec sequence was played back at 20 frames per sec.  This speeds up the animation by a factor of 200 times.  Open Office 2.0 has the tools to produce an animated "gif" image.   Without the timelapse and rapid playback, it is very difficult to discern the motion of the clouds.  Without producing an animated "gif" image, a slide viewer that permits rapid playback of sequential images shows the animation very well.  Irfanview (by Irfan Skiljan - available free for personal use from irfanview.com) works very well for Windows.





Physics Photo of the Week is published weekly during the academic year on Fridays by the Warren Wilson College Physics Department.  These photos feature an interesting phenomena in the world around us.  Students, faculty, and others are invited to submit digital (or film) photographs for publication and explanation.  Atmospheric phenomena are especially welcome.  Please send any photos to dcollins@warren-wilson.edu.


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