Abstract
Regular monitoring of the D- and F-layers of ionosphere over Central Asia territory is being performed on the permanent basis starting year 2008 when one Very Low Frequency (VLF) receiver and two SuperSID receivers were provided to Uzbekistan IHY cite by Stanford University. The results obtained at Tashkent IHY (International Heliophysical Year) station are applied to earthquake electromagnetic precursors, lightning, and Solar flares and to ionospheric disturbances originating from gamma ray flares of Soft Gamma-Ray Repeaters. Regular monitoring of the D-layer of ionosphere over Central Asia territory has been performed on the permanent basis. Several Solar events are observed and the analysis has shown that there is simultaneous correlation between the times of change of amplitude of the waves and the Solar flares. Features of the lightning discharge generated by radio atmospherics are studied and its effectiveness in D-region ionosphere diagnostics is examined. We have mainly analyzed GPS derived TEC disturbances from two GPS stations located in Tashkent and Kitab, for possible earthquake ionospheric precursors. The solar and geomagnetic conditions were quiet during occurrence of the selected more than 30 earthquakes. We produced TEC time series over both sites and apply them to detect anomalous TEC signals preceding or accompanying the earthquakes. The results show anomalous enhancements which are examined in the earthquakes.
Highlights
The ionizing action of the radiation of Sun on the upper atmosphere produces free electrons
We have observed significant changes in amplitude parameters, a few days before the strong EQs occurred on the path way from the transmitters to Tashkent Very Low Frequency (VLF) receiver
The obtained results are in good agreement with the previous observations of EQs precursors in VLF data reported by various researchers [Hayakawa, Fujinawa, 1994; Pulinets, Boyarchuk, 2004]
Summary
The ionizing action of the radiation of Sun on the upper atmosphere produces free electrons. About 60 km the number of these free electrons is sufficient to affect the propagation of electromagnetic waves This “ionized” region of the atmosphere is a plasma and is referred to as the ionosphere. The ions are formed by the ionization of atmospheric neutrals by X-ray radiation and solar Lyman α radiation This region vanishes at night due to the combination of the ions and electrons. To the D layer, the E layer shows a diurnal behavior with a maximum of ionization at local noon In this region, ions consist primarily of O2+ produced by the absorption of solar radiation, and NO+ formed by charge transfer collisions with other ions ionized by coronal X-rays.
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