Modifications of Middle Atmosphere Conductivity During Sudden Ionospheric Disturbances Deduced From Changes of Schumann Resonance Peak Frequencies

摘要

This paper presents a novel technique to reveal modifications of the Schumann resonance peak frequencies during sudden ionospheric disturbances (SIDs) caused by the solar X-ray flares. An SID is associated with the abrupt reduction in ionospheric height over the day hemisphere during solar flares. Reduction of the daytime ionosphere lowers the average height of the Earth-ionosphere cavity and leads to an increase in its resonant frequencies. An improved profile is used describing the middle atmosphere conductivity and its modification. The resonance frequencies of the Earth-ionosphere cavity and the characteristic heights of the conductivity profile are computed by the full wave technique for various intensities of ionosphere modifications. Power spectra of the vertical electric field component are calculated using the 2-dimensional telegraph equations for the uniform spatial distribution of global thunderstorms in the cavity with the day-night nonuniformity for several observer positions relative to the solar terminator. Changes in the peak frequencies are obtained as a function of magnitude of ionosphere modifications. The weighted average frequency of Schumann resonance is calculated over the first three modes, and the linear fitting is performed for the dependence of this weighted average frequency on the SID intensity and/or on changes in the magnetic characteristic height of the conductivity profile. The data obtained might be used in further interpretations of observational data and in estimating the lower ionosphere modification by using Schumann resonance records.