In this study we investigate the APE density in a TC simulated by the axisymmetric model of Rotunno and Emanuel . The APE density is defined for each parcel as the work released when an air parcel moves from its initial position to its level of neutral buoyancy in a reference state. We derive the form of the APE density from the model equations, and use a simple time-evolving reference state of mean horizontal density to show that the majority of APE density in the modelled TC is at the sea surface and in the eyewall region, as expected. We test other proposed formulations of APE density to examine how the definition of the reference state affects the apparent distribution of APE.
Using a Boussinesq approximation, we can identify APE generation and dissipation terms arising due to the diffusion of heat and water vapour to establish the relative importance of these processes. We question whether the choice of reference state can affect whether a given process appears to be a source or sink of APE.