Clearing Up Clouds!

Clouds form when air is cooled to its dewpoint or the temperature, if the air is cooled, it reaches saturation. Air can reach saturation in a number of ways. The most common way is through lifting. As a bubble or parcel of air rises it moves into an area of lower pressure (pressure decreases with height). As this occurs the parcel expands. This requires energy, or work, which takes heat away from the parcel. So as air rises it cools. This is called an adiabatic process.

The rate at which the parcel cools with increasing elevation is called the "lapse rate". The lapse rate of unsaturated air (air with relative humidity <100%)>dry lapse rate. This means for each 1000 feet increase in elevation, the air temperature will decrease 5.4°F! Once air is saturated, the air cools at a lower rate.


Image Courtesy of www.srh.noaa.gov