Coupling of ELF/ULF energy from lightning and MeV particles to the middle atmosphere, ionosphere, and global circuit

Abstract

In an attempt to explain numerous atmospheric electrical phenomena, the elements of the global electrical circuit are reexamined. In addition to being a "quasi-static "DC" generator" and source of radiated energy at VLF and higher, the thunderstorm is found to be a pulse generator, with most of the external energy contained in ELF and ULF pulse currents to the ionosphere (and Earth). The pulse energy is found to deposit largely in the middle atmosphere above the thunderstorm. The VLF and above components are well understood, as are the ULF components due to the conductivity gradient. However, a previously poorly understood ELF component on the millisecond timescale, or "slow tail," contains a large fraction of the electrical energyø This component couples strongly to the ionosphere and also launches a unipolar transverse electromagnetic (TEM) wavelet in the radial Earth-ionosphere transmission line. The increase in charge with distance associated with such wavelets, and their ensemble sum at a point, may explain some large mesospheric "DC" fields but there are still difficulties explaining other than rare occurences, except for antipodal reconvergence. These millisecond duration unipolar wavelets also couple to the ionosphere and may trigger other lightning at a distance. A schema is elucidated by which the charge of MeV particles deposited in the middle atmosphere persists for much longer than the local relaxation time. This also gives rise to unipolar waves of global extent which may explain lower-latitude field perturbations associated with solar/ geomagnetic eventso Introduction One of the best established "solar-terrestrial" relations is the observed short-term response of atmospheric electrical parameters (local "ionospheric potential," fair weather electric field and air-Earth current) to solar flares and related events, yet the classical "DC" picture of atmospheric electricity does not readily provide an explanation of such phenomena. To provide a framework for studying these phenomena, a reexamination of the elements of the "global circuit" is performed, and shows a coexisting "AC" or pulse circuit, with much more energy than that due to the "DC" or "radiated" components, and which may be more subject to "external" influences. Also considered is the coupling of this AC energy, most of which is at ELF/ULF frequencies, to the middle atmosphere, and to the ionosphere and "global circuit." It is suggested that some large mesospheric vertical fields, such as those observed by U.S. and Russian groups, may be due to unipolar transverse electromagnetic (TEM) wavelets propagating in the Earth-ionosphere cavity. These wavelets may explain the strong ELF/[JI,F spectrum in the Earthionosphere cavity and the mechanism by which high-energy particle precipitation events, as well as other lightning, may trigger lightning.The definition of the various frequency ranges used in this paper is the traditional definition which developed over many decades, in which ELF is in the range of about 10 to 3000 Hz, with UI.F below th...

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