Adiabatic Temperature Changes

Rising and Subsiding Air

Rising air experiences a drop in temperature, even though no heat is lost to the surrounding environment. Air is a poor conductor of heat, so a rising air parcel will tend to remain discrete from the surrounding air, not mixing rapidly. The temperature drops because there is a decrease in atmospheric pressure at higher altitudes. As the pressure of the surrounding air is reduced, the rising air parcel will expand. This results in cooling, since there is an inverse relationship between the volume of an air parcel and its temperature. During either expansion or compression, the total amount of energy in a discrete parcel of air remains the same (none is added or lost). The energy can be used either to do the work of expansion or to maintain the temperature of the parcel, but not both. If no heat is added or lost to the surroundings, then when an air parcel rises and expands, its temperature drops. Conversely, when the parcel is compressed, its temperature rises. So if the parcel of air descends into altitudes where the pressure is greater, it would be compressed and would warm up again without taking in heat from the outside.

This is the process of adiabatic heating and cooling. The term adiabatic implies a change in temperature of the air parcel without gain or loss of heat from outside the air parcel. Air parcels may rise or subside in the atmosphere as the result of variations in temperature and of the dynamics of the atmosphere, and this in turn affects their pressure and temperature. Adiabatic processes are very important in the atmosphere, and the cooling of rising air is necessary for cloud formation.

Adiabatic Lapse Rates