Adiabatic processes are those in which no heat transfer takes place. In an atmospheric adiabatic process, a parcel of air undergoes changes in its internal temperature but does not lose or gain heat to its ambient (surrounding) environment. According to Boyle’s law, air, like any gas, experiences changes in pressure proportionate to changes in volume: When a parcel of air expands to fill more space, it decreases in pressure. When it contracts to fill less space, the air parcel increases in pressure.As air rises, it expands, and as it descends, it is compressed. This is due to ambient pressures around the parcel of air: A given parcel of air that is near the Earth’s surface has a great deal of air above it, weighing it down and increasing its total pressure. By contrast, a parcel of air that is higher up in the atmosphere has less air above it and thus less pressure upon it. As air parcels circulate in the atmosphere, they expand or contract until they reach a state of pressure equilibrium with other air parcels around them. At the same time, their internal temperatures decrease as they expand and increase as they contract. These adiabatic processes changes in temperature can be observed and Adiabatic processes mathematically averaged into what are known as “lapse rates.”
Adiabatic processes There are three lapse rates to be considered. First, the environmental lapse rate is the most common baseline rate of change of the overall atmosphere as one ascends into it. This rate is 4° Celsius per 1,000 meters of altitude. Thus, for every 1,000 meters one ascends off the ground, one observes a drop in temperature, on the average, of 4° Celsius. (The atmosphere can also be in a state of inversion, in which temperatures increase rather than decrease as one ascends.)The next lapse rate is the dry adiabatic lapse rate, which applies to air parcels that are not saturated with moisture. Adiabatic processes This rate is 10° Celsius per 1,000 meters. Adiabatic processes as an air parcel rises and cools, its temperature may approach its dew point, meaning that it may become saturated with moisture, causing water vapor to condense into liquid water. In the process of condensation, heat is released, and cooling begins to take place at a slower pace (because of the injection of heat into the ambient environment). This slower rate of cooling, known as the wet adiabatic lapse rate, is about 5° Celsius per 1,000 meters adiabatic processes.