VLF group delay of lightning-induced electron precipitation echoes from measurement of phase and amplitude perturbations at two frequencies
Article first published online: 20 SEP 2012
Copyright 1990 by the American Geophysical Union.
Journal of Geophysical Research: Space Physics (1978–2012)
Volume 95, Issue A3, pages 2457–2462, 1 March 1990
How to Cite
1990), VLF group delay of lightning-induced electron precipitation echoes from measurement of phase and amplitude perturbations at two frequencies, J. Geophys. Res., 95(A3), 2457–2462, doi:10.1029/JA095iA03p02457., and (
- Issue published online: 20 SEP 2012
- Article first published online: 20 SEP 2012
- Manuscript Accepted: 14 AUG 1989
- Manuscript Received: 17 OCT 1988
Measurement of phase and amplitude perturbations (trimpis) of the NWC signal at Dunedin at both the NWC frequencies, 22,250 Hz and 22,350 Hz, enables measurement of the received phase of the echo signal (phasor difference of the perturbed and unperturbed signals) at each frequency and so the rate of decrease of phase with frequency. This, of course, is the group delay. The 100-Hz difference implies that measurement of echo group delays of up to 5 ms could be made without ambiguity, though other factors limit this to about 2.5 ms. Some 38 “difference trimpis” during May and June 1988 showed echo delays up to 2 ms corresponding to reflection from points displaced more than 1000 km from the NWC-Dunedin great circle path. The echo amplitudes observed at such large displacements are much greater than expected from smooth circular depressions of the ionosphere modifying the waveguide phase velocity and so imply sharper discontinuities in the waveguide.