Potential Vorticity Mixing, Dynamic Efficiency of Latent Heat Release, and the Rapid Intensification of Supertyphoon Haiyan (2013)

The inner-core dynamics in tropical cyclone (TC) on rapid intensification (RI) is studied with a 2-km resolution full-physics cloud-resolving model in Supertyphoon Haiyan (2013). The potential vorticity (PV) field in the simulated storm indicates elliptical and polygonal-shaped eyewall in the low and middle levels during the RI onset. The PV budget analysis suggests the importance of PV mixing at this stage. Namely, the asymmetric transport of PV to the storm center from the diabatically generated PV in the eyewall while ejecting PV filament outside the eyewall. We employ the piecewise PV inversion (PPVI) and omega equation calculations to aid the balanced dynamics diagnosis. Our PPVI calculation indicates that the PV mixing accounts for about 50% of the central pressure falling during RI onset. The omega equation diagnosis suggests dynamical warming in the eye which is associated with the PV mixing. The eye core pressure decrease causes a significant increase in the boundary layer (BL) inflow. The BL inflow led to the contraction of the radius of the maximum tangential wind (RMW) and the formation of symmetric convective PV towers inside of RMW. The eye in the later stage of the RI is warmed by the subsidence associated with the convective PV towers. A dynamic efficiency factor (DEF) based on axisymmetric gradient wind vortex theory is introduced to further aid the diagnosis of RI. The DEF measures the local efficacy of convective heating in generating kinetic energy. The DEF is large in the presence of strong baroclinicity near the eyewall. Our results highlight the collaborative nonlinear effects of eye-core pressure decrease with the PV mixing, the increase of the symmetric BL radial inflow, and the symmetric convective PV tower which is co-located with the large DEF area during the RI period. An experiment with 500-m resolution shows that the convergence of the BL inflow can lead to a magnitude of 20 m/s updraft and convective PV towers with a peak value of 200 PV unit.