VLF and LF signatures of mesospheric/lower ionospheric response to lightning discharges
- Stanford Univ., Stanford, CA (United States)
- Phillips Laboratory, Hanscom Air Force Base, MA (United States)
New evidence is presented of disturbances of the electrical conductivity of the nighttime mesosphere and the lower ionosphere in association with lightning discharges. In addition to extensive documentation of the characteristics of a class of event heretofore referred to as early/fast VLF events [Inan et al.], this data reveal a new feature of these events, consisting of a postonset peak that typically lasts for 1-2 s. The authors also report the observation of short-duration VLF or LF perturbation, in which the amplitude of the subionospheric signal exhibits a sudden change within 20 ms of the causative lightning discharge, and recovers back to its original level in < 3 s. These short-duration events have characteristics similiar to the previously observed rapid onset, rapid decay VLF signatures [Dowden et al.]. Both the typical and rapidly recovering events are observed primarily when the causative lightning discharge is within {+-}50 km of the VLF or LF great circle propagation path, indicating that the scattering from the localized disturbance is highly collimated in the forward direction. The latter in turn implies that for the parameters in hand, the transverse extent of the disturbance must be at least {approximately} 100-150 km. The measured VLF signatures are compared with the predictions of a three-dimensional model of subionospheric VLF propogation and scattering in the presence of localized ionospheric disturbances produced by electromagnetic impulses and quasi-electrostatic (QE) fields produced by lightning discharges. The rapidly recovering or short-duration events are consistent with the heating of the ambient electrons by quasi-static electric fields, in cases when heating is not intense enough to exceed the attachment or ionization thresholds. When no significant electron density changes occur, the conductivity changes due to heating alone last only as long as the QE fields, typically less than a few seconds. 29 refs., 12 figs.
- OSTI ID:
- 255048
- Journal Information:
- Journal of Geophysical Research, Journal Name: Journal of Geophysical Research Journal Issue: A3 Vol. 101; ISSN JGREA2; ISSN 0148-0227
- Country of Publication:
- United States
- Language:
- English
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