Low-frequency ionospheric sounding with Narrow Bipolar Event lightning radio emissions: regular variabilities and solar-X-ray responses

A. R. Jacobson (1) , R. Holzworth (1) , E. Lay (1) , M. Heavner (2) , D. A. Smith (3)

1 Department of Earth and Space Sciences [Seattle]
2 Physics Dept.
3 ISR Division

We present refinements of a method of ionospheric D-region sounding that makes opportunistic use of powerful (10⁹?10¹¹ 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-?s), 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.

Domaines: Océan, Atmosphère; Sciences de la Terre

A. R. Jacobson, R. Holzworth, E. Lay, M. Heavner, D. A. Smith. Low-frequency ionospheric sounding with Narrow Bipolar Event lightning radio emissions: regular variabilities and solar-X-ray responses. Annales Geophysicae, 2007, 25 (10), pp.2175-2184. ⟨hal-00318399⟩