The concept of Isentropic Potential Vorticity in rotating planar fluids is shown
to be a special case of a physical system with a divergence free, hence
conserved, Topological Torsion 3-form. The physical system is presumed to be
described by a 1-form of Action, and the evolutionary process is presumed to be
described by a singly parameterized contravariant vector field. The induced
differential 1-form of Work is constrained such that its Pfaff dimension is 2.
The resulting dynamics is thermodynamically reversible. The methods have
application to weather forcasting and do not require that the evolution of the
rotating compressible fluid be isentropic.