Modeling the Impact of Secondary Ice Production on the Charge Structure of a Mesoscale Convective System

The charge structure in thunderstorms may be strongly affected by different secondary ice production (SIP) processes, but has not been well understood. In this study, the impacts of three SIP mechanisms on microphysics and electrification in a squall line are investigated using model simulation, including the rime-splintering, ice-ice collisional breakup, and shattering of freezing drops. The parameterization of the three SIP mechanisms, a noninductive and an inductive charging parameterization are implemented in the spectral bin microphysics. The results show that with SIP processes included, the modeled radar reflectivity is more consistent with observation. It is found that both the mass and concentrations of graupel/hail are enhanced by SIP processes, while the diameter decreases. The mixing ratio of ice/snow decreases due to the rime-splintering, and increases in mixing ratio are due to the shattering of freezing drops. Particle charging is significantly affected by SIP, leading to a dipole structure of the total charge density, which includes a lower negative and an upper positive charge region. With both the noninductive and inductive charging considered, the charge carried by graupel/hail changes from negative to a bipolar structure, and the charge sign carried by ice/snow is inverted due to the SIP. The modeled lightning activity is enhanced by implementing all three SIP processes, while if only considering the rime-splintering process, the flash rate would be suppressed. The insights obtained from this study highlight the importance of considering different mechanisms of SIP in modeling the charge structure and lightning activity in thunderstorms. Electrification in thunderstorms is strongly related to microphysics, especially the ice-phase processes. However, the ice microphysics in deep convective clouds is very complicated, and the impacts of different ice-phase processes on cloud electrification are not well understood. One of the unresolved questions is how the charge structure in thunderstorms can be affected by various secondary ice production (SIP) mechanisms. Until now, only a small number of studies have investigated this issue, and most of them focused on a single SIP (rime-splintering process). However, recent studies have shown that other SIP mechanisms, especially the shattering of freezing drops and ice-ice collisional breakup, can greatly enhance ice generation in convective clouds. Therefore, the various mechanisms of SIP may potentially have strong impacts on the charge structure in thunderstorms. In this study, the parameterizations of three different mechanisms of SIP, as well as the noninductive and inductive charge parametrization are implemented in a spectral bin microphysics model scheme in WRF (Weather Research and Forecasting model). A squall line is modeled to investigate the impacts of the three mechanisms of SIP on charge structure and flash rate. The results highlight the importance of considering various mechanisms of SIP in modeling cloud electrification and lightning. The impacts of three secondary ice production (SIP) mechanisms on the electrification of a squall line is investigated using a model The SIP processes have strong impacts on the cloud microphysics, resulting in significant modification of charge structure The flash rate is suppressed by rime-splintering, while enhanced by ice-ice collisional breakup and shattering of freezing drops