What phenomenon occurs when the temperature decreases in a rising parcel of air, leading to the formation of clouds?

Adiabatic cooling is the correct answer because it describes the process where a rising parcel of air expands and cools as it ascends in the atmosphere. When air rises, it encounters lower atmospheric pressure, which allows it to expand. This expansion leads to a decrease in temperature, as the air does work on its surroundings.

As the temperature of the rising air drops, it can reach its dew point, the temperature at which air becomes saturated with moisture. When this occurs, the moisture in the air begins to condense around tiny particles, forming clouds. Understanding adiabatic cooling is crucial in physical geography, as it plays a significant role in cloud formation and weather patterns.

While humidity increase, condensation around particles, and pressure instability are relevant factors in weather systems, they do not specifically describe the cooling process of rising air that leads directly to cloud formation. For instance, humidity increase refers to the amount of moisture in the air, while condensation around particles occurs as a result of cooling rather than directly defining the cooling process itself. Pressure instability involves factors that can lead to air movement but does not explain the cooling associated with adiabatic processes.