This project develops improved models that incorporate recent experimental data to give a substantially improved understanding of thunderstorms as generators in the Earth's global electric circuit. Part 1 involves developing a spherical geometry model of a realistic thunderstorm embedded in a realistic, conducting atmosphere. The storm is modeled with layers of steady state currents that are adjusted to reproduce typically observed vertical electric field (E) profiles from different storm types. The model is then applied to large mesoscale convective systems (MCSs), to more typical small storms, and to unscreened convective updrafts by using appropriate vertical electric field profiles. The results of Part 1 will show how different types of storms drive different amounts of current between the Earth and the ionosphere in the global circuit.
In Part 2 the model is expanded to handle transient currents associated with lightning flashes. The transient current model is applied to MCSs and to small thunderstorms, and the results will be added to those of Part 1. Through this work the relative importance of transient currents in the global circuit will be deduced.
Finally, a global scale examination will be undertaken that incorporates these improved estimates of the several 'thunderstorm components' in the circuit, including mesoscale convective systems, small thunderstorms, unscreened convective cores, and above-cloud transients caused by lightning flashes. The relative contribution of each of these components will be estimated.
The overall intellectual merit of this project derives from combining all of the proposed modeling results for the contribution of MCSs, small storms, and their associated transients, with estimations of the number and type of thunderstorms occurring simultaneously on the Earth. This synthesis will provide a state-of the-art estimate of the current that is driven in the global circuit by all simultaneous thunderstorms. This new estimate will be compared to the discharging currents that occur in the fair weather portion of the globe. From this, the overall importance of thunderstorms in the global electric circuit and the overall charge on the Earth can be determined. An estimate of the importance of other contributors to the global circuit, such as non-thunderstorm shower clouds, will also be possible.
The broader impacts of this project derive partly from the international collaboration that are extended and expanded throughout the studies. The investigators, graduate students, and undergraduate students will conduct the work in close collaboration with established scientists and young scientists, graduate students, and undergraduate students at the Institute for Applied Physics in Russia. The primary Russian collaborators (one of whom is a recent Ph.D. Candidate) and one graduate student will visit the investigators' laboratory in the U.S. for extended periods. This collaboration also involves an integration of theoretical plasma physicists (Russian collaborators) with experimental atmospheric physicists (U.S. investigators). This exchange will lead to new methods of investigation and discovery for both groups. Another broader impact of the project involves the gender diversity of the scientists and students: one of the U.S. investigators and at least one of the U.S. students are female, and women remain an underrepresented group in physics and in atmospheric physics, especially. Mentorship, training, and education of the undergraduate and graduate students involved will enhance their abilities to become independent researchers in this or another field of science. Publication and dissemination of the results will contribute to better understanding of the global electrical circuit, which is intimately tied to global climate through the global thunderstorm activity.
