Absolutely Unstable

Absolutely Unstable lapse rate plotted on a skew-T diagram

On this plot, if a parcel of air with temperature T and dewpoint Td is lifted, it will move along the dry adiabat until it reaches saturation at Point T1. At every point in its ascent, the parcel is warmer than the surrounding air (line T-T'). As a result, the air along path T-T1 will be warmer and less dense that the surrounding air. Consequently, it will continue to rise of its own accord. This air is said to be absolutely unstable. The sounding lapse rate from T-T’ exceeds dry adiabatic and is therefore commonly referred to as a superadiabatic lapse rate.

Note that absolute instability is a relatively rare condition that is usually confined to a shallow layer near the surface under conditions of strong surface heating (for example, solar heating or very cold air over warm water).

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