Concentric eyewall formation in Typhoon Sinlaku (2008) – Part II: Dynamical analyses

Numerous hypotheses about concentric eyewall formation have been proposed in the literature. However, few of them were fully investigated by high-spatial/ temporal-resolution observations or simulations with more realistic settings. The mechanism(s) determining the secondary eyewall formation has been not well answered yet. In part I of this work, a unique high-spatial/temporal-resolution and model/observation- consistent dataset had been generated for Typhoon Sinlaku (2008) during September 9-13. Simulations of Sinlaku starting at different initial time are further investigated. It is striking that some of the simulations are able to capture the secondary eyewall cycle, while the others started earlier with fewer data assimilated are not. This provides a unique opportunity to study the dynamical processes of the concentric eyewall formation in Sinlaku. Here in part II of this study, we explore the dynamical processes of the concentric eyewall formation as generated from the dataset and experiments described in part I. The BSA (beta-skirt axisymmetrization) formation hypothesis is examined. Not only the axisymmetric components but also asymmetric features of the potential voritcity gradient (beta-skirt) and filamentation time scale are calculated. In addition, kinetic energy spectrum is also evaluated to investigate the energy cascade of disturbances prior to the formation of the concentric eyewall. Investigation of other related hypotheses, such as the effect of both moisture and sheared vortex Rossby waves, are also ongoing. We believe that thorough analyses of this high-spatial/temporal-resolution and model/observation-consistent dataset would provide valuable physical insights into the physics of concentric eyewall formation.