The effect of subionospheric propagation on whistlers recorded by the DEMETER satellite – observation and modelling

Abstract

Abstract. During a routine analysis of whistlers on the wideband VLF recording of the DEMETER satellite, a specific signal structure of numerous fractional-hop whistlers, termed the "Spiky Whistler" (SpW) was identified. These signals appear to be composed of a conventional whistler combined by the compound mode-patterns of guided wave propagation, suggesting a whistler excited by a lightning "tweek" spheric. Rigorous, full-wave modelling of tweeks, formed by the long subionospheric guided spheric propagation and of the impulse propagation across an arbitrarily inhomogeneous ionosphere, gave an accurate description of the SpW signals. The electromagnetic impulses excited by vertical, preferably CG lightning discharge, exhibited the effects of guided behaviour and of the dispersive ionospheric plasma along their paths. This modelling and interpretation provides a consistent way to determine the generation and propagation characteristics of the recorded SpW signals, as well as to describe the traversed medium.

Ionosphere Waves Service (IWS) – a problem-oriented tool in ionosphere and Space Weather research produced by POPDAT project

“…The proposed explanation is: Ducted whistler-mode UWB signals, propagating in different ducted mode wave-form, crossed each other in FFT pattern; see in Figure 6b. In other cases a regular fractional hop whistler was recorded together with a higher SpW signal mode propagating alone; see in Figure 7a and the modeled FFT in Figure 7b (Ferencz et al 2007). These signals have no such characteristic shapes as the whistler-like signals.…”

“…A typical series of low-latitude whistler pairs is in Figure 3. (e) Spiky whistlers (SpW), which UWB signals are generated by lightning and propagated in the Earth-ionosphere wave-guide before the out-coupling from this waveguide to traverse the ionosphere and going into the magnetosphere (Ferencz et al 2007). (f) Swallow-tailed whistlers (STW): These UWB signals have whistler character in their main trace, also exhibiting additional wave structure as strong signal trace splitting and deviation on broadband spectra, with a shape of swallow-tail see in Fig.…”

Remote sensing of D-region ionosphere using multimode tweeks

“…When the firstorder mode cutoff frequency of tweek is less than the electron gyrofrequency, then f H ) f p is satisfied and Eq. (7) replaced as follows [8]:…”

“…The tweek waveforms are better resolved and suffer less attenuation at night (typically \0.5 dB Mm -1 as compared to 5 dB Mm -1 during daytime) due to sharper D-region electron density profiles [4]. Dispersion analysis of tweeks yields information about the state of the D-region ionosphere along the path of propagation [5][6][7][8][9][10].…”

Development of an automatic procedure to estimate the reflection height of tweek atmospherics

“…Ferencz (2004) presented a new theoretical model of waveguide and numerical solutions of the model. Ferencz et al (2007) recently reported by using VLF recordings on board the DEMETER satellite that specific signals of fractional hop whistlers, "Spiky Whistler", are excited by tweeks.…”