VLF/LF Remote Sensing of Transient and Localized Disturbances of the Lower Ionosphere Associated with Lightning Discharges,

High resolution measurements of subionospheric VLFLF signals are now established as a powerful remote sensing tool for investigation of transient and localized ionospheric disturbances associated with atmospheric lightning discharges. Events usually consist of sudden 2 s changes in amplitude andor phase followed by relatively slow 10-100 s recovery to background levels. This paper discusses recent results from a new series of observations conducted at Arecibo, Puerto Rico and at Huntsville, Alabama. The subionospheric VLF paths from two different transmitters to these two sites are nearly collinear, allowing for identification of the location of the disturbed ionospheric regions. Events observed on some very short paths indicate that selective excitation of waveguide modes can be used to extract information on the energy spectra of precipitating particles. In one case, on 23 February 1990, an extremely high rate of event activity 60 eventshr was observed at Huntsville on the 48.5 kHz signal from Silver Creek, Nebraska, with amplitude changes of as much as 15 dB in individual events.