Probing geomagnetic storm-driven magnetosphere–ionosphere dynamics in D-region via propagation characteristics of very low frequency radio signals

Abstract

The amplitude and phase of VLF/LF radio signals are sensitive to changes in electrical conductivity of the lower ionosphere which imprints its signature on the Earth-ionosphere waveguide. This characteristics makes it useful in studying sudden ionospheric disturbances, especially those related to prompt X-ray flux output from solar flares and gamma ray bursts (GRBs). However, strong geomagnetic disturbance and storm conditions are known to produce large and global ionospheric disturbances, which can significantly affect VLF radio propagation in the D region of the ionosphere. In this paper, using the data of three propagation paths at mid-latitudes (40, we analyze the trend of aspects of VLF diurnal signal under varying solar and geomagnetic space environmental conditions in order to identify possible geomagnetic footprints on the D region characteristics. We found that the trend of variations generally reflect the prevailing space weather conditions in various time scales. In particular, the 'dipping' of mid-day signal amplitude (MDP) of VLF always occurs after geomagnetic perturbed or storm conditions in the time scale of 1-2 days. The mean signal before sunrise (MBSR) and mean signal after sunset (MASS) also exhibit storm-induced dipping, but they appear to be influenced by event's exact occurrence time and highly variable conditions of dusk-to-dawn ionosphere. We observed fewer cases of the signals rise (e.g., MDP, MBSR or MASS) following a significant geomagnetic event, though this effect may be related to storms associated phenomena or Preprint submitted to Atmospheric and Solar-Terrestrial Physics March 10, 2016 effects arising from sources other than solar origin. The magnitude of induced dipping (or rise) significantly depends on the intensity and duration of event(s), as well as the propagation path of the signal. The post-storm day signal (following a main event, with lesser or significantly reduced geomagnetic activity), exhibited a tendency of recovery to pre-storm day level. In the present analysis, We do not see a well defined trend of the variations of the post-storm sunrise terminator (SRT) and sunset terminator (SST). The SRT and SST signals show more post-storm dipping in GQD-A118 propagation path but generally an increase along DHO-A118 propagation path. Thus the result could be propagation path dependent and detailed modeling is required to understand these phenomena.

Diagnostic study of geomagnetic storm-induced ionospheric changes over VLF signal propagation paths in mid-latitude D-region

“…The size, shape and behaviour of the magnetosphere (formed by the interaction between the solar wind and the Earth's magnetic field) are controlled by the varying properties of the solar wind plasma and the embedded magnetic fields (McPherron et al, 2008). Solar-induced geomagnetic footprints in the magnetosphere are coupled to the ionosphere through the linkage of the Earth's magnetic field despite their large distance apart, thus making the regions physically connected into a single global system (Nwankwo et al, 2016). Geomagnetic storms (and associated substorms) are the leading driver of large-scale coupled magnetosphere-ionosphere perturbations in the geospace, and are mainly product of strong variations in solar wind conditions via energy transfer.…”

“…These manifestations can modify atmospheric parameters (Nwankwo et al, 2016), leading to irregularities that can affect the operational capabilities of space-based systems and alteration of the reflection conditions for radio waves propagating in the Earth-ionosphere waveguide (EIWG). Substantial progress has been made in understanding global dynamics and large-scale coupling of the upper ionosphere using both ground-based observational capabilities (e.g., Global Navigation Satellite System (GNSS) receivers, vertical and oblique high frequency (HF) sounding, atmospheric radar (coherent and incoherent scatter radars)) and space-based satellite systems (e.g., Advance Composition Explorer (ACE), Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC), Defense Meteorological Satellite Program (DMSP), Geostationary Operational Environmental Satellite (GOES) etc.)…”

“…The study of trends in variation of diurnal VLF narrowband is proving to be useful to understand space weather effects in the lower ionosphere (e.g. Araki T. (1974); Kikuchi and Evans (1983); Kleimenov et al (2004); Peter et al (2006); Cliverd et al (2010); Kumar and Kumar (2014); Tatsuta et al (2015); Nwankwo et al (2016)), as well as ionospheric changes from other atmospheric and lithospheric sources. Solar flare/X-ray flux-induced ionospheric disturbances in the D-region are normally detected as a sudden change in VLF amplitude and phase.…”

“…Solar flare/X-ray flux-induced ionospheric disturbances in the D-region are normally detected as a sudden change in VLF amplitude and phase. The VLF detection mechanism of flare-induced sudden ionospheric disturbances (SID) in D region are described in Nwankwo et al (2016). The signal can also be significantly affected by geomagnetic disturbances and/or storm-induced ionosphere perturbations (Kikuchi and Evans, 1983).…”

Solar flare induced cosmic noise absorption

“…Stauning, 1996], resulting in the so-called 'Sudden Ionospheric Disturbances' (SIDs), and the associated absorption is known as sudden cosmic noise absorption (SCNA). Nwankwo et al (2016) identified merits in studying sudden ionospheric disturbances related to prompt X-ray flux output from solar flares. The duration of SCNA absorption is usually of the order of the flare [Stauning, 1996;Longden et al, 2007].…”