Electrification and lightning in idealized simulations of a hurricane-like vortex subject to wind shear and sea surface temperature cooling.

Abstract

elationships between intensity fluctuations, cloud microphysics, lightning variations and electrical structure within idealized tropical cyclones are investigated with the cloud-resolving Collaborative Model for Multiscale Atmospheric Simulation (COMMAS). An initial strong tropical cyclone is subjected either to steady-state control conditions (CTRL), increased wind shear (SHEAR), or a reduction in sea surface temperature (SST).In CTRL, nearly all the lightning (>95%) occurred in the outer region (100 km < r ≤ 300 km) and was overall very episodic in the inner core (r ≤ 100 km), consistent with observations. The inner core updrafts were weaker and experienced greater depletion of cloud water by warm rain processes, which, in contrast to the deeper updrafts in the rainband convection, reduced the mixed-phase cloud depth and confined the bulk of the charging and lightning initiations to lower levels.Notably larger flash rates were produced in the asymmetric inner core of the SHEAR case, with the majority of the flashes located in the downshear left quadrant, consistent with prior observational works. In contrast to CTRL, the more vigorous inner core convection in SHEAR resulted in the formation of a prominent negative charge region and enhanced production of negative ground flashes.With a nearly identical filling rate as SHEAR, the introduction of cooler sea surface temperatures in the SST case caused lightning activity to fade rapidly in both the inner core and rainbands.