Wideband Analysis of Sources and Structure of the Earth-Ionosphere Waveguide

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

This study is concerned with the electromagnetic waves produced by lightning and propagating worldwide in the natural waveguide formed by the conductive surface of the earth and the conductive ionosphere. Measurements are under way with a new antenna to monitor the height of this waveguide using the energy of individual lightning flashes, with the goal of detecting changes in the height. Such changes can arise from the ionizing effects of lightning flashes, or from changes in ionizing radiation from the sun or outer space. The so-called quality factor of the waveguide is also scrutinized to investigate global variations in ionizing radiation from space. A second major task involves the characterization of electrical current that flows in vertical lightning channels. The mathematical theory for electromagnetic waves in the ELF (Extremely Low Frequency) region of the electromagnetic spectrum is used in conjunction with electric field measurements to infer the history of the lightning current. These currents are then used to understand the behavior of transient luminous phenomena such as sprites, elves, and haloes, which occur over large thunderstorms. Broader scientific impacts arise from the global implications of the observations, which enable access to evidence of global change both within the waveguide (the troposphere) and external to the waveguide (the sun and outer space). The educational impacts involve the international collaboration almost guaranteed by problems of a global nature, and the entrainment of MIT undergraduate students early in their scientific careers.