Estimating the lower ionosphere height and lightning location using multimode “tweek” atmospherics

Abstract

There is proposed a new method of estimating the effective ionospheric height of the Earth-ionosphere waveguide and the propagation distance of tweek-atmospherics. It is based on the compensation of waveguide frequency dispersion of a tweek signal, which enables us to improve the accuracy of deducing the cutoff frequencies, especially in the presence of noise. An approach to solve the inverse problem is suggested that reduces the task of finding both the source range and the waveguide cutoff frequencies by using the multimode characteristics of tweeks to an issue of onedimensional optimization. Based on the numerical modeling of multimode tweek-atmospherics in the Earth-ionosphere waveguide with exponential vertical conductivity profile of the lower ionosphere, it was shown that the accuracy of estimating the effective waveguide height by the new method is good as about 100-400 m for the first and higher order modes. It then allows us to estimate the parameters of vertical conductivity profile of the lower ionosphere for a wide range of source distances from a few hundred to a few thousand kilometers, as long as two or more tweek harmonics can be detected. Preliminary analysis of experimental tweek records show a decrease of the effective height with increasing the mode number, and the scale height of the exponential vertical conductivity profile for the isotropic lower ionosphere model is estimated to be in a range of 0.4-2.5 km.

Remote sensing of D-region ionosphere using multimode tweeks

“…This supports our consideration that the ionosphere is not sharply bounded at a fixed height for all harmonics but can be considered as sharply bounded progressively at higher altitudes for increasing order of harmonics of tweeks. The presented results are consistent with those estimated by others [9,22,23]. Multistation observations have their own importance, and they can contribute significantly in making profiles of facts obtained from each individual station.…”

“…1(a)-1(d) of tweeks. The normal reflection height of the VLF waves in the ionosphere varies with frequency, lower frequencies usually reflected from lower heights due to relatively lower electron densities [23]. Table 1 lists the computed value of reflection heights for tweeks and their higher modes showed in Fig.…”

“…Ionospheric parameters such as reflection height of tweeks, equivalent electron densities at reflection height, propagation distance and geographic locations of the source discharge have been estimated successfully using tweeks as a diagnostic tool [9,[18][19][20][21][22][23]. But earlier studies relied on only the first and the second harmonics of tweeks.…”

“…But earlier studies relied on only the first and the second harmonics of tweeks. Very little attention has been devoted experimentally to the use of multimode tweeks [16,22] that represent the higher-order modes of the EIWG, along with some numerical studies [23,24]. In comparison with previously used system, we have more precise instruments and better recording facility nowadays.…”

Low-frequency (ELF�VLF) radio atmospherics study at the Ukrainian Antarctic Akademik Vernadsky station

“…In the present paper, we apply the advanced Kharkov technique (Shvets et al, 2014(Shvets et al, , 2017. The experiments performed at Ukrainian Antarctic Akademik Vernadsky station during February-April 2019 measurement campaign allowed locating sources of tweek atmospherics at distances of up to 10000 km with concurrent estimating of temporal variations of the effective height of the ionosphere during the night (Shvets et al, 2019).…”