Helicity production and maintenance in a baroclinic atmosphere

A canonical, maximum symmetric form of the helicity balance equation in a baroclinic fluid with two independent variables of state (e.g., in a 'dry atmosphere') is reviewed. It is emphasized that the baroclinicity per se is incapable of producing helicity. An analogy between helicity and thermodynamic entropy is sketched, e.g., with regard to reversible and irreversible atmospheric processes. Under the Boussinesq approximation, the canonical helicity balance equations are applied to analyze two distinct self-consistent versions of an approximate asymptotic solution for a helical Rankine-like vortex, embedded in a convectively unstable boundary layer. The proposed methodology may be regarded as a prototype for diagnostics and validation of more complex and realistic vortex models.