An Observational Study of Quasi-Periodic Lightning Activity in the Inner Core of Super Typhoon Hato (2017) Before Landfall

In 2017, Super Typhoon Hato was characterized by pronounced convective asymmetries in its inner core immediately before landfall in China. Together with the asymmetric convection, quasi-periodic lightning activities occurred concurrently, with a period of approximately 3 hours. This study discussed the characteristics of short-cycle lightning activity and corresponding polarimetric radar quantities in the inner core of Super Typhoon Hato (2017) before its landfall. Although the strongest inner-core convection was located persistently in the downshear and downshear-left quadrants, the lightning bursts behaved quasi-periodically with a cycle of about 3 hours. The analysis revealed that wavenumber-2 vortex Rossby waves (VRWs) were present in the inner core, propagating cyclonically and intensifying downshear left. When the positive perturbation of the VRWs was coupled with the VWS-forced convective enhancement, the local convection was significantly reinforced. Moreover, the slanted updrafts intensified by the phase-locking between VRW activity and convection strengthened by VWS can invigorate the growth of graupel, probably through riming processes, and further enhance the charge separation and lightning production immediately outside the eyewall. The invigorated graupel growth accompanied by lightning outbreaks can enhance surface precipitation and more efficient warm-rain growth below the melting layer. The radar observations demonstrated that when other VRWs were excited and propagated to the left side of the shear, the abovementioned phase-locking occurred again, leading to increased volumes of graupel and updrafts near the eyewall and short-cycle lightning bursts. On the basis of radar observations, a set of numerical simulations will be conducted to investigate the physical mechanism of lightning production.