Charge structure and lightning sensitivity in a simulated multicell thunderstorm

Abstract

A three‐dimensional dynamic cloud model is used to investigate electrification of the full life cycle of an idealized continental multicell storm. Five laboratory‐based parameterizations of noninductive graupel‐ice charge separation are compared. Inductive (i.e., electric field‐dependent) charge separation is tested for rebounding graupel‐droplet collisions. Each noninductive graupel‐ice parameterization is combined with variations in the effectiveness of inductive charging (off, moderate, and strong) and in the minimum ice crystal concentration (10 or 50 L−1). Small atmospheric ion processes such as hydrometeor attachment and point discharge at the ground are treated explicitly. Three of the noninductive schemes readily produced a normal polarity charge structure, consisting of a main negative charge region with an upper main positive charge region and a lower positive charge region. Negative polarity cloud‐to‐ground (CG) flashes occurred when the lower positive charge (LPC) region had sufficient charge density to cause high electric fields. Two of the three also produced one or more +CG flashes. The other two noninductive charging schemes, which are dependent on the graupel rime accretion rate, tended to produce an initially inverted polarity charge structure and +CG flashes. The model results suggest that inductive graupel‐droplet charge separation could play a role in the development of lower charge regions. Noninductive charging, on the other hand, was also found to be capable of producing strong lower charge regions in the tests with a minimum ice crystal concentration of 50 L−1.