When does a subadiabatic lapse rate occur?

A subadiabatic lapse rate occurs when the surrounding air cools slower than the plume. This situation typically arises in stable atmospheric conditions, where the environmental lapse rate (the rate of temperature decrease with altitude in the surrounding air) is less than the dry adiabatic lapse rate, which is the rate at which a parcel of unsaturated air cools as it rises.

In these conditions, the air surrounding a rising plume of warmer air (such as from a smoke stack or thermal plume) moves upward, but the environmental temperature decreases at a slower rate compared to the rate at which the plume's temperature decreases. As a result, the plume remains warmer relative to the surrounding air for a longer period, which can lead to a more stable environment where vertical mixing is inhibited. This is significant in environmental engineering and meteorology, as it can affect dispersion patterns of pollutants and influence local weather conditions.

Identifying the subadiabatic lapse rate is crucial for understanding how thermal plumes interact with the atmosphere and how they might spread or dissipate.