The influence of symmetric and non-symmetric charge configurations on the possibility of sprite inception: Numerical experiments with a 3D electrostatic model

摘要

We present a simple, efficient, and flexible three-dimensional electrostatic model for calculating the magnitude and direction of the electric field from the ground to the base of the ionosphere for a given thunderstorm charge configuration, with the aim of evaluating the possibility for sprite inception. The model is based on a method-of-images solution to Poisson's equation, assuming near vacuum conditions and with perfectly conducting upper and lower boundaries. A dipole electrical structure within each thundercloud is assumed, with a screening (shielding) charge above the cloud. The charge centers (main positive, main negative, and screening charge) are modeled with average structural characteristics of summer and winter thunderstorms. To simulate a positive or negative cloud-to-ground lightning discharge, the main positive or main negative charge center, respectively, is removed from the domain. The computed electric potential at each grid point is converted to the electric field and is compared against the value of the conventional breakdown field to obtain an indication of the possibility of electrical breakdown and hence the possibility of sprite inception. This simple model is particularly useful for performing a sensitivity study with respect to variation in thunderstorm cell charge configuration, with no assumption of symmetry in the horizontal or vertical directions. Implications of the presence of neighboring clouds at different relative stages of development on the possibility of sprite inception and on the displacement of sprites from the location of the parent thunderstorm are also examined, as well as clouds with inverted dipole charge configuration.