Dynamic vortex initialization for tropical cyclone predictions utilizing PV-ω equation and nudging

Abstract

To improve the initial vortex structure for tropical cyclones (TCs) in numerical predictions, this study proposes a dynamic vortex initialization procedure that combines the inversion of PV-ω equation with the Grid Nudging technique. A statistical relationship between precipitation rate and latent heating profiles is first derived from numerical model simulations. In practice, the GPM-IMERG satellite-retrieved precipitation rate is used to derive the heating rate, which then drives the PV-ω equation to obtain the secondary circulation of the TC. In order to construct a physically realistic thermodynamic field in the initial TC set up, the Grid Nudging technique is employed. In this process, the momentum fields are anchored, enabling the adjustment between the thermodynamic and the momentum fields to occur through model integration.

Application of this dynamic initialization procedure on the simulation of Typhoon Lekima (2019) successfully improves the prediction of Lekima's rapid intensification. The asymmetrical secondary circulation, constrained by satellite-retrieved precipitation rates, along with the reasonable thermodynamic structure and momentum fields, contribute to forecast improvement. Furthermore, during the rapid intensification phase, the model simulation captures key characteristics of upper-level asymmetric convective activity under vertical wind shear, such as strong upward motion in the upshear-left quadrant, which could result in an “outflow blocking” mechanism consistent with observations.