An examination of thunderstorm‐charging mechanisms using a two‐dimensional storm electrification model

Abstract

Abstract. The early, prelightning, electrification of a storm resulting from noninductive (NI) charging involving graupel, cloud ice/snow, and supercooled cloud water in a riming environment is studied using a comparative approach in a two-dimensional storm electrification model. The primary schemes examined are NI charge transfers based on the laboratory work of Takahashi [1978] and Saunders et al. [1991 ]. The NI mechanism, based on Takahashi's work, develops a positive dipole (positive charge above negative) and electric fields approaching 185 kV m-'as the cloud enters the dissipating stage. Charge transfers, based on the work of Saunders and colleagues, had to be reduced in magnitude to produce electrification that is consistent with the observations. In addition, the Saunders scheme produces an initially inverted dipole (negative charge above positive) which resolves to a positive dipole in the latter part of the simulation and produces electric fields approaching 250 kV in '•. Sensitivity tests show that the NI scheme, based on Takahashi's work, is sensitive to the number concentration of ice crystals, whereas the Saunders-based scheme is much less sensitive to ice crystal numbers. The Saunders parameterization has strong positive charging of graupel at low effective liquid water content and low temperature. This positive charging can result in an unusual cloud-top charge structure when used at full value but is benign when the charging is reduced in magnitude. The charge structure resulting from the Saunders scheme is quite sensitive to the calculation of the effective water content, which determines the level of charge reversal. Both of the NI schemes are capable of producing electrification that approaches thunderstorm levels.

Charging of ice-vapor interfaces: applications to thunderstorms

“…6c). Takahashi's complete data set, which is consistent with the later studies of Pereyra et al (2000) and Takahashi and Miyawaki (2002), successfully models thunderstorms (Helsdon et al, 2001) and shows that the tripolar nature of thunderstorms arises in part from the boundary in T − ρ l space between negative and positive graupel charging. Due to the "knobbly" shape of graupel, precise surface conditions are un- known; but estimates in Williams et al (1991) indicate that the graupel surface 1. has vapor-grown frost due to the relatively low surface temperature at the lowest ρ l values (regime of mostly positive charging), 2. sublimates due to the relatively high surface temperature on the graupel at middling ρ l values (mostly negative charging), and 3. has liquid water at the highest ρ l values (positive charging).…”

“…This ice-ice inductive charge transfer increases the thunderstorm charging rate after the noninductive ice crystalgraupel mechanism establishes a strong field (Helsdon et al, 2001). Previously, researchers have assumed that these induced charges are transferred by conduction during brief, melt-free collisions (e.g., Illingworth and Caranti, 1985).…”

CELLS v1.0: updated and parallelized version of an electrical scheme to simulate multiple electrified clouds and flashes over large domains

“…The Storm Electrification Model with an electrification and lightning flash scheme was pioneered by Helsdon and Farley (1987) and Helsdon et al (1992). It was used to investigate the charge structure and the Maxwell currents in an idealized storm (Helsdon et al, 2001) and then to study the lightning-produced NO x (Zhang et al, 2003a,b). Sun et al (2002) adopted the electrical scheme of Helsdon et al (1992) to simulate the feedbacks of cloud electricity on convection.…”

Cloud-scale model intercomparison of chemical constituent transport in deep convection

“…The treatment of electrical processes follows Helsdon and Farley (1987) and Helsdon et al (2001). Each hydrometeor class has an associated charge density in addition to the positive and negative small ion concentrations that combine to form the total charge density, which is related to the electrical potential through Poisson's equation.…”