Under which condition does air experience adiabatic heating?

Adiabatic heating occurs when a parcel of air is forced to subside and compress. As the air descends, it experiences an increase in pressure due to the weight of the air above it. This increased pressure leads to a corresponding increase in temperature without any heat exchange with the surrounding environment, which is the key characteristic of adiabatic processes.

When air is compressed, its molecules are forced closer together, resulting in a higher temperature. This phenomenon is crucial in understanding how weather systems behave, particularly in high-pressure areas where sinking air can lead to warmer surface temperatures.

In contrast, when air is cooled (as in an ascent where it expands), it experiences adiabatic cooling, not heating. Similarly, when moisture condenses, it releases latent heat but does not directly contribute to adiabatic heating in the context of compressing air parcels. Thus, the concept of air being forced to subside and compress directly ties to the process of adiabatic heating, making this the correct answer.