Adiabatic and Diabatic Potential Vorticity (PV) Dynamics of an Intensifying Tropical Cyclone

It is well known that diabatic processes in the core of a tropical cyclone are an important contributor to the dynamic and thermodynamic structure. Vigorous deep convection in the eye-wall provides a source of latent heating near the storm center that sustains and intensifies the system. Convective instability is inherently chaotic, even in regions of forced ascent such as the eye-wall, and so diabatically produced positive and negative potential vorticity (PV) anomalies rely on additional dynamical processes to self-organize. As the storm intensifies, positive PV anomalies merge and are retained within the core vortex and negative anomalies are expelled to the periphery.

In this study, the problem of analyzing the PV dynamics of the intensifying storm is reduced to a thin-layer approximation of the 320K isentrope. A “full physics” case study simulation of Typhoon Sinlaku is performed using the Weather Research and Forecasting (WRF) model and a 24-hr window during the intensification phase is extracted for evaluation. The initial 320-K PV field is used to initialize a simplified 2-dimensional non-divergent beta-plane model covering a comparable domain, which is subsequently integrated forward in time. In this paper we investigate the results of both simulations in order to dissect the respective roles of adiabatic and diabatic vortex dynamics in intensification.