ENVIRSC 1A03 Chapter Notes - Chapter 7: Lifted Condensation Level, Fluid Parcel, Adiabatic Process
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At the earth"s surface an air parcel has the same temperature and pressure as the surrounding air. The air pressure around the air parcel lowers, allowing the air molecules inside the parcel to push against its walls (expansion). Because there is no other energy source the air molecules must use some of its own energy to expand, resulting in a lower temperature and lower molecular speeds. The squeezing, increases the parcel"s temperature and the air molecules speed. As an air parcel rises it expands and cools. When an air parcel sinks, it contracts in size and heats. If this occurs with no interchange in heat, this is then called an adiabatic process. If the air in the parcel is unsaturated, the relative humidity is below. 100%, the rate of adiabatic cooling or warming, remains constant this rate is represented by the equation above. This rate applies only to unsaturated air aka dry adiabatic lapse rate.