Low-frequency ionospheric sounding with Narrow Bipolar Event lightning radio emissions: regular variabilities and solar-X-ray responses
We present refinements of a method of ionospheric D-region sounding that makes opportunistic use of powerful (10<sup>9</sup>–10<sup>11</sup> W) broadband lightning radio emissions in the low-frequency (LF; 30–300 kHz) band. Such emissions are from "...
| Main Authors: | , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2007-11-01
|
| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/25/2175/2007/angeo-25-2175-2007.pdf |
| Summary: | We present refinements of a method of ionospheric D-region sounding that
makes opportunistic use of powerful (10<sup>9</sup>–10<sup>11</sup> W) broadband
lightning radio emissions in the low-frequency (LF; 30–300 kHz) band. Such
emissions are from "Narrow Bipolar Event" (NBE) lightning, and they are
characterized by a narrow (10-μs), simple emission waveform. These
pulses can be used to perform time-delay reflectometry (or "sounding") of
the D-region underside, at an effective LF radiated power exceeding by
orders-of-magnitude that from man-made sounders. We use this opportunistic
sounder to retrieve instantaneous LF ionospheric-reflection height whenever
a suitable lightning radio pulse from a located NBE is recorded. We show how
to correct for three sources of "regular" variability, namely solar zenith
angle, radio-propagation range, and radio-propagation azimuth. The residual
median magnitude of the noise in reflection height, after applying the
regression corrections for the three regular variabilities, is on the order
of 1 km. This noise level allows us to retrieve the
D-region-reflector-height variation with solar X-ray flux density for
intensity levels at and above an M-1 flare. The instantaneous time response
is limited by the occurrence rate of NBEs, and the noise level in the height
determination is typically in the range ±1 km. |
|---|---|
| ISSN: | 0992-7689 1432-0576 |