A Study of the Contribution of Thunderstorms to the Global Electric Circuit Using a Time Dependent Numerical Model and a Fractal Model

Open Access
Author:
Mallios, Sotirios
Graduate Program:
Electrical Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
April 01, 2015
Committee Members:
  • Victor P Pasko, Dissertation Advisor
  • Victor P Pasko, Committee Chair
  • John David Mathews, Committee Member
  • Michael Matthew Micci, Committee Member
  • Timothy Joseph Kane, Committee Member
Keywords:
  • Global Electric Circuit
  • Thunderstorm
  • Lightning
Abstract:
The Global Electric Circuit (GEC) is a circuit that is formed between the Earth's surface, which is a good conductor of electricity, and the ionosphere, a weakly-ionized plasma at ~80 km altitude. Thunderstorms are believed to be the major charging sources of this circuit. In this dissertation, we present our studies on the contribution of thunderstorms to the Global electric Circuit. We examine the current that is driven to the ionosphere and to the ground before, during and after single negative cloud-to-ground (CG) and intra-cloud (IC) lightning discharges. A numerical model has been developed, that calculates the quasi-electrostatic field before the lightning, due to the slow accumulation of the charge in the thundercloud, and after the lightning by taking into account the Maxwellian relaxation of the charges in the conducting atmosphere and accounting for the dissipation stage of the thunderstorm development. From these results, the charges that are transferred to the ionosphere and to the ground are calculated. We demonstrate the significance of considering the pre-lightning and the dissipation stages and accounting for realistic distribution of the conductivity inside of the thundercloud for the accurate calculation of the charge flow to the ionosphere and to the ground. We show that the charge transfer to the ionosphere depends mainly on the altitudes of the charges inside the thundercloud and their spatial separation. The amount of charge that is transferred to the ground, due to currents flowing in the vicinity of the thundercloud during a transient time period following a lightning discharge, is significantly affected by the conductivity distribution in the thundercloud and can be several times smaller than the amount of charge that is transferred to the ionosphere during the same time period. Moreover, we show that the duration of each of the thunderstorm life cycle stages affects the results. Furthermore, we show the influence of the corona currents on the overall current system. We extend the model to include the whole domain of the GEC. We investigate different types of boundary conditions for the proper modeling of the global current flow in the presence of a single storm and the resulting potential difference that is created. We compare this model in the steady state limit with a static model that has been developed in previous published studies. We apply the model to a case of an experimentally measured thunderstorm. We investigate the Wilson current that flows from its top towards the ionosphere as a function of a sequence of different types of lightning discharges, the flash rate and the conductivity distribution. We compare the results with the measurements and we make conclusions regarding the validity of the modeling concept. We develop a time-dependent fluid model that is able to calculate self consistently the time dynamics of the conductivity distribution along with the time dynamics of the thunderstorm electrical properties. This model takes into account several atmospheric processes such as the ionization due to the galactic cosmic rays radiation, the ion-ion recombination, and the attachment of ions to cloud particles. We study the regimes at which the previous models that assume constant conductivity over time are valid and we quantify the similarities and differences between these two models. Finally, we model the lightning discharge channel using a three-dimensional cartesian fractal model. The purpose of this model is to simulate several types of lightning discharges that occur in realistic thunderstorms and calculate the amount of charge that is removed or neutralized from each thunderstorm. At the same time we used this model to quantify the potential differences produced in a developing IC lightning discharge for given thunderstorm electric configurations. We present a case of a +IC lightning discharge in a realistic thunderstorm configuration that leads to a very high (~300 MV) potential difference, and show how a delay in the development of the negative leader with respect to the positive one in a bidirectional leader system can facilitate a high potential difference in the negative leader head region, which favors the production of terrestrial gamma ray flashes. Terrestrial gamma ray flashes are high energy (up to 100 MeV) photon bursts originating from the Earth's atmosphere in association with IC lightning discharges.