Abstract
Measurements of the amplitude and phase of very low frequency transmitter signals were used to evaluate the effects on the ionosphere of a moderate intensity solar flare that occurred on 13 December 2007. These measurements were compared to modelled results from the Long Wave Propagation Capability code. The ionospheric effects were found to be delayed by ~1 min with respect to the 0.1–0.8 nm solar X-ray flux.
Highlights
Waveguide propagationVery low frequency (VLF) radio waves span the frequency interval 3–30 kHz
Together with VLF observations, Long Wave Propagation Capability (LWPC) was used to examine the evolution of the amplitude and phase perturbations for the entire duration of the solar flare that occurred on 13 December 2007
A C4.5 solar flare that occurred on 13 December 2007 produced perturbations in the VLF amplitude and phase on mid-latitude subionospheric paths during winter
Summary
Very low frequency (VLF) radio waves span the frequency interval 3–30 kHz. The surface of the Earth is a good conductor at VLF, especially over the oceans. The ionosphere represents a conducting surface for VLF waves. The passage of the seasons has an impact on local ionospheric characteristics. Both of these variations are stable and predictable. The D-region (about 60–90 km above the Earth’s surface) is the lowest part of the ionosphere and is maintained during the day mainly by Lyman- α radiation from the sun which ionises nitric oxide.[1] It is convenient to characterise the D-region by a height-dependent conductivity[2]: ωr (z) = ω02 / v = 2.5 x 105 exp(β(z — H )), Equation 1 where ω0( s-1 ) is the electron plasma frequency and v is the effective electron-neutral collision frequency.
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