  Adiabatic and inviscid axisymmetric perturbations to a stable reference
vortex in gradient wind balance are known to experience two kinds of restoring
forces: one that is proportional to both the perturbation density and the
reference pressure gradient, and one that is purely radial and proportional to
the squared angular momentum perturbation. We show that the work required to
move a fluid parcel against such forces from its equilibrium to actual position
is path-independent and formally equivalent to the available energy accounting
for momentum constraints previously constructed by Andrews (2006) and Codoban
and Shepherd (2006). Physically, this work represents the energy of the
unbalanced part of the vortex and hence a form of eddy energy. It can be
partitioned into available acoustic energy, slantwise available potential
energy and centrifugal potential energy. We show that the conditions required
for these energies to be positive definite correspond to the classical
conditions for symmetric stability, valid for both small and finite-amplitude
perturbations. The new available energy framework possesses various
advantageous features over previous approaches that shed new light on how the
thermodynamic and mechanical sinks/sources of energy control the
intensification of the balanced and unbalanced parts of a warm core cyclonic
vortex. These features should prove useful in the future to re-examine and
clarify the links between the different existing paradigms of tropical cyclone
(TC) intensification within a single unifying theoretical framework.
