Physics Photo of the Week
Wave Clouds - ground level and satellite photos
On August 9, 2009, while traveling on Interstate 81 in northern
Virginia, I noticed the parallel clouds running NE to SW, parallel to
the mountain ridges and took ground-level photographs from my cell
phone in the car. Intrigued, I later found the archive collection
of weather satellite images of the area. The satellite images not
only show the same cloud formations, but they also show the
mountain/ridge system of the central Appalachian Mountains of the
area. The mountain ridges are parallel to the cloud crests.
The clouds thus appear to have been formed by winds blowing over the
mountain ridges. Traversing the mountain ridges, the air rises
until it cools, then descends again, repeating many times as the winds
continue to blow toward the southeast toward Baltimore and
From the size of the features on the state lines of the satellite
photo, and scaling from Google Earth images, the cloud ridges are about
6 miles apart. From the lateral offset of the cloud shadows, the
time of day (11:00 am), the heights of the clouds are calculated to be
about 4000 feet (7.5 miles), well above the elevation of the Appalacian
mountain ridges. See PPOW
March 16, 2007 for more of an explanation.
Photo of the
published weekly during the academic year on Fridays by the Warren
Wilson College Physics
Department. These photos feature 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 firstname.lastname@example.org.
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