3. Stability

Determining Stability » Stability Types Neutral Equilibrium

Skew-T showing dry and saturated neutral lapse rates

If the temperature curve of a sounding is parallel to a saturation adiabat, then a saturated parcel displaced upward would be neither aided nor hindered by the surrounding atmosphere and would tend to remain at the level to which it is displaced. In this case, the upward displaced saturated parcel is in neutral equilibrium with the environment.

Similarly, if the T curve of the sounding parallels a dry adiabat, an unsaturated parcel displaced upward would also tend to remain at the level to which it is displaced. Therefore, the upward-displaced unsaturated parcel is in neutral equilibrium with the environment.

Note the adiabatic assumption inherent in the parcel method requires downward displacement of all parcels to be dry adiabatic, whether the parcel is saturated or unsaturated. Therefore, all downward-displaced parcels will be in neutral equilibrium if the sounding exhibits a dry adiabatic lapse rate.