Ann Vshihara, age 13, of Costa Mesa, California, for her question:

What is the adiabatic process?

An adiabatic process blew into the column about the Chinook wind. Since it is a very tricky process, it deserves a fuller explanation of how it works in a more general way. Chemists use the terms adiabatic or isotropic to describe changing temperatures within a closed system. The same process confines a system of heat transfer in a weather event, when a wind blows up, over and down a mountain.

This complex process concerns a temperature change that does not perform as usual. Heat, of course, is a form of energy that causes molecules to move faster. Normally it uses several methods to spread and share its energy with its cooler surroundings. Normally it spreads until an object and its surroundings are equally cool or warm. In an adiabatic process, temperature changes are prevented from spreading.

This unusual event may occur in chemical processes or in weather events. Chemical activities either use heat energy or give off heat energy to perform their miraculous changes. Usually this energy is taken from or shared with the surroundings. An adiabatic process occurs when a barrier of some sort confines a heat exchange to a self contained system.

Another example occurs when gases are compressed. When a gas is squeezed, or compressed it becomes warmer and its faster molecules try to spread. But if the gas is sealed in a metal tank and compressed, the heat cannot spread and we have an adiabatic change of temperature that does not involve the surroundings.

The atmosphere is a global turmoil of mingling gases. It would seem to be the least likely place where enclosed adiabatic processes can occur. However, sometimes the surrounding air limits the path of a wind or confines a mass of light rising air. Then a limited air mass may lose or gain heat without involving the atmosphere around it.

This may happen when a prevailing wind meets a mountain. As the warm air from a sunny valley pushes up the slope, it expands and cools as the pressure around it decreases. The cooled breezy air moves over the hump and the process is reversed as it slides down the slope. The Descending wind piles up and compresses, creating its own self contained heat.

This adiabatic cooling and heating process involves only the air mass that moves over the mountain. And the process is quite precise. For every 2,000 feet the upslope wind ascends, its temperature cools ten degrees. For every 2,OOO.feet the down slope wind descends, it gains ten degrees. The adiabatic cooling equals the adiabatic heating.

Another adiabatic weather event creates the high flying clouds. Air near the surface absorbs heat and moisture from land and sea. The warm air expands and carries its gaseous vapor aloft. A mile or so above the earth, the cooler air has a surplus of vapor which is changed into misty cloud moisture. The warm rising air cooled itself and created clouds by a self contained adiabatic process.