Physics Photo of the Week

October 6, 2006
Foggy Farm

On September 24, 2006 I happened to have my camera early in the morning near the Physics Department at Warren Wilson College.  I was thus able to capture this spectacular view of the morning fog on the Warren Wilson College Farm.

Morning fog is very common in the late summer/early fall.  Usually the fog is all-encompasing - obscuring everything in the valley with no scenic views until the fog "burns" off.  The fog on this late September morning was unusual in that it was confined to a small area.

Fog consists of suspended water droplets.  Each droplet is about 10 micrometers (1 x 10^-5 m).  The droplets are formed from condensing water vapor when cooled below the dew point.  Clear nights allow the ground to cool below the dew point.  The reason that fog forms in late summer/early fall more than the spring and mid summer is that the weather patters have generally changed to much clearer air allowing the ground level air to cool at nights.  Not only are the cool nights responsible for more morning fog in the early fall, but the leaves and vegatation are still transpiring, releasing much water vapor into the atmosphere. (This is the suggestion posed by my wife Vicki).  The combination of high humidity and clear nights, create more instances of fog.

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