Static stability
= Static stability
{title2=$N^2$}
Resistance of a stratified fluid to a small vertical parcel displacement. For dry homogeneous air, $N^2=(g/\theta)d\theta/dz$ in terms of <potential temperature>; $N^2>0$ gives a restoring <buoyancy> force. Moisture and composition gradients modify the parcel comparison. Across an ideal sharp interface, a denser lower fluid is stable to an infinitesimal interchange.