On the relationships between convective storm kinematics, microphysics, and lightning

Abstract

Combined multiparameter radar, dual-Doppler, thermodynamic sounding, and lightning observations of 11 thunderstorms (6 from the mid-latitudes, 5 from the tropics) are presented. The thunderstorms span a wide spectrum of intensities, from weak monsoon-type to severe tornadic, and include both unicellular and multicellular convection. In general, the kinematically strongest storms featured lower production of negative cloud-to-ground lightning (typically < 1 min-1 flash rates for large portions of the storms' lifetimes) when compared with more moderate convection, in accord with an elevated charge mechanism. The only significant differences between intense storms that produced predominately positive cloud-to-ground (CG) lightning for a significant portion of their lifetimes (PPCG storms), and intense storms that produced little CG lightning of any polarity (low-CG storms), was that PPCG storms featured much larger volumes of significant updrafts (both > 10 m s-1 and > 20 m s-1) and produced greater amounts of precipitation (both rain and hail). Otherwise, peak updrafts and vertical air mass fluxes were very similar between the two types of storms, and both types were linked by anomalously low production of negative CG lightning. It is suggested that PPCG storms may be caused by enhanced lower positive charge created by the larger volume of significant updrafts. Since both PPCG and Iow-CG storms are capable of being severe, anomalously low production of negative CG lightning (regardless of positive CG flash rate) may be a useful signature for use in the "now casting" of severe convection.