What occurs to air as it sinks in the atmosphere?

When air sinks in the atmosphere, it experiences an increase in pressure due to the weight of the air above it. This increased pressure compresses the air, which in turn raises its temperature. As air is compressed, the molecules are forced closer together, leading to an increase in kinetic energy, which manifests as a rise in temperature. This phenomenon is a fundamental aspect of adiabatic processes in atmospheric science.

In contrast, the other choices describe processes that do not occur when air sinks. For example, air cannot decrease in pressure and cool when it is descending; instead, it is subject to increasing pressure and warming. The idea that air remains at constant pressure and temperature contradicts the dynamics at play when air is displaced by surrounding air. Lastly, air cannot become lighter and rise while it is sinking; the act of sinking is counter to the notion of rising air, which is typically associated with lighter, less dense air that is heated and expands.