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Ann. Geophys., 26, 1793-1803, 2008
www.ann-geophys.net/26/1793/2008/
© European Geosciences Union 2008
Low-frequency ionospheric sounding with Narrow Bipolar Event lightning radio emissions: energy-reflectivity spectrum
A. R. Jacobson1, R. Holzworth1, and X.-M. Shao2
1Earth and Space Sciences, University of Washington, Seattle, WA, USA
2ISR Division, Los Alamos National Laboratory, Los Alamos, NM, USA
Abstract. We analyze data on radio-reflection from the D-region of the lower
ionosphere, retrieving the energy-reflection coefficient in the frequency
range ~5–95 kHz. The data are the same as developed for a recent
study of ionospheric-reflection height, and are based on recordings of
powerful (multi-Gigawatt) radio emissions from a type of narrow (~10 μs) lightning discharge known as "Narrow Bipolar Events". The
sequential appearance of first the groundwave signal, and then the
ionospheric single-hop reflection signal, permits us to construct the
energy-reflection ratio. We infer the energy reflection's statistical
variation with solar zenith angle, angle-of-incidence, frequency, and
propagation azimuth. There is also a marginally-significant response of the
energy reflectivity to solar X-ray flux density. Finally, we review the
relationship of our results to previous published reports.
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