Most simply, fog is visible air. On the ground we call it fog; in the air we call it a cloud. We see it when the air contains minute, but visible, water or ice particles. The temperature at which the air cools enough so that the water vapor in the air condenses, forming tiny droplets, is called the dew point.

The Fog Chamber is another exhibit made for NCAR by the Exploratorium Museum. The pump handle on the exhibit lets visitors increase the air pressure (and temperature) of the air inside. But when the visitor pushes the exhibit’s brass button, decreasing the pressure, the temperature inside falls to the dew point, and visible water vapor can be seen in the bright spotlight.

To learn how various divisions at NCAR incorporate fundamental weather concepts such as the dew point into their research studies, click on a project affiliated with the Mesoscale and Microscale Meteorology (MMM) Division at http://box.mmm.ucar.edu/uswrp/; check out similar research projects within the Atmospheric Technology Division (ATD) at http://www.atd.ucar.edu/facilities.html.