What characterizes an absolutely unstable atmosphere?

An absolutely unstable atmosphere is characterized by the condition wherein parcels of air continue to rise regardless of whether they are saturated or not. This occurs when the environmental lapse rate—the rate at which temperature decreases with altitude—is greater than the dry adiabatic lapse rate for unsaturated air. When an air parcel is forced to rise, it expands and cools; however, if it is less dense than the surrounding air, it will continue to rise. In this scenario, even if the air parcel becomes saturated and starts to cool at the moist adiabatic lapse rate, it is still buoyant enough to ascend even further.

This condition leads to significant vertical air movement, often resulting in the development of convection, clouds, and possibly severe weather phenomena such as thunderstorms. The ability of the air parcel to rise regardless of its humidity status highlights the fundamental instability present in the atmosphere under these conditions.