Physics Photo of the Week
of September 13, 2007 I noticed the rising smoke from a fire just east
of Warren Wilson College in front of the Four Brothers' Knobs.
The smoke, however, did not rise very far. The smoke was trapped
by a thermal inversion.
Normally, air at higher altitudes is cooler than air at lower
altitudes. Warm smoke thus can become more bouyant as it rises
and reaches surrounding air that is cooler and more dense than the
smoke. During nights where there is little wind, the cooler air
settles into the valleys and falls below a layer of warmer air.
The warm air on top of the layer of cool air is called the thermal
inversion. See the PPOW
18, 2005 for another example of smoke trapped by an
During most days when the sun heats the earth surface in the valleys,
convection breaks up the inversion and any smoke can then
reach high altitudes and dissipate. If the nights are windy, the
wind also breaks up the inversion. Inversions tend to form during
very quiet nights when the cool air sinks to the valley floor.
See the drawing at right.
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.
All photos and discussions are copyright by Donald
Collins or by the person credited for the photo and/or
discussion. These photos and discussions may be used for private
individual use or educational use. Any commercial use without
written permission of the photoprovider is forbidden.
see the Physics Photo
the Week Archive.
Observers are invited to submit
digital photos to: