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 
mountains, 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.
Click
here to see the Physics Photo
of
the Week Archive.
Observers are invited to submit
digital photos to:
