Physics Photo of the Week

August 29, 2008

Rainsquall
On August 26, 2007, the day before classes at WWC began a year ago I had the opportunity to photograph a coming rainstorm and to obtain an animation of the falling curtain of rain.  This was one of the last rain events of late summer 2007 before extensive drought plagued western North Carolina.

The mountains shown at the extreme bottom of the photo are Watch Knob (the small conical peak in the foreground at left-center).  The flat-top mountain just behind Watch Knob is called White Oak Flats.  During the photography event this curtain of rain fell between Watch Knob and White Oak Flats.  Interpolating from the known distances of these
Animated image - have patience while loadingmountains, the rain squall was about 6 km from the camera during the sequence.

Notice in the time lapse animation how the direction of the falling changes about half-way from cloud to ground due to the wind shear.  The wind at ground level is different from the winds aloft.

From the time taken for the rain to fall, the estimated distance to the rain, and the calculated field of view of the camera, the rain was falling about 10 m/sec (22 mi/hr).  This seems reasonable for large raindrops. 

Soon after the sequence of images, a hard rain fell at the location of the camera (about 1 inch in 30 minutes).  By that time I had retreated indoors with the camera and tripod!



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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