Geopotential surface
= Geopotential surface
{title2=$\Phi=\mathrm{constant}$}
A surface on which <geopotential> is constant. Effective <gravity> is perpendicular to it. In a local constant-gravity approximation these surfaces are horizontal; comparing their slopes with <isopycnals> identifies the geometry permitting an <adiabatic parcel exchange> to release <available potential energy>.