Dear Tom,

It is windy around here so much! What causes wind?

Wayne Grossmer, Calumet City

Dear Wayne,

The fundamental cause of wind is unequal heating of the air. For example, on a warm and sunny summer afternoon the air over Chicago is warmer than the air over Lake Michigan. Because cool air is more dense than warm air, a given volume of cool air will weigh more than the same volume of warm air. The greater weight of the cool air causes it to exert greater pressure and air pressure differences will in turn cause air to more from higher to lower pressure. We perceive this movement as wind. In the example above, cool air over Lake Michigan, possessing greater density and air pressure than warmer air over Chicago, will push inland, generating the familiar lake breeze.