Published: 2008-03-20 10:13:17
Updated: 2008-03-20 10:13:17
Posted March 20, 2008
By Bill Bevan
MIKE MOSS SAYS: Bill, There are a couple of mechanisms by which the clouds may "go away." One is by a process called advection, meaning simply that the cloud droplets are moving along at roughly the speed of the wind at cloud height, so that the clouds are carried by the wind in the direction toward which the wind is blowing, until the clouds have moved out of the area and the sky clears up.
The other mechanism is by evaporation, in which the cloud droplets themselves are transformed from tiny liquid water droplets into invisible water vapor molecules. This can result from warming of the air in in which the cloud resides, which may occur due to solar heating or due to subsidence (sinking air) and the resulting increase in pressure, which also increases temperature, or from entrainment of drier air that may surround the cloud - as this drier air is mixed into the cloud the overall relative humidity decreases and the cloud droplets, again, may evaporate, leaving the skies clear or mostly so.
In many cases, the clearing of our skies in the wake of a cloudy period or a storm system is some combination of these various mechanisms.