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.
During the geomagnetic disturbances, the geomagnetically induced current (GIC) are influenced by the geoelectric field flowing in conductive Earth. In this paper, we studied the variability of GICs, the time derivatives of the geomagnetic field (dB/dt), geomagnetic indices: Symmetric disturbance field in H (SYM-H) index, AU (eastward electrojet) and AL (westward electrojet) indices, Interplanetary parameters such as solar wind speed (v), and interplanetary magnetic field (Bz) during the geomagnetic storms on 31
Abstract. The ionosphere is the major error source for the signals of global
positioning system (GPS) satellites. In the analysis of GPS measurements,
ionospheric error is assumed to be somewhat of a nuisance. The error induced by
the ionosphere is proportional to the number of electrons along the line of
sight (LOS) from the satellite to receiver and can be determined in order to
study the diurnal, seasonal, solar cycle and spatial variations in the
ionosphere during quiet and disturbed conditions. In this study, we
characterize the diurnal, seasonal and solar cycle variation in observed
total electron content (OBS-TEC) and compare the results with the
International Reference Ionosphere (IRI-2016) model. We obtained TEC from a
dual-frequency GPS receiver located at Birnin Kebbi Federal Polytechnic
(BKFP) in northern Nigeria (geographic location: 12.64∘ N,
4.22∘ E; 2.68∘ N dip) for the period 2011–2014. We
observed differences between the diurnal variation in OBS-TEC and
the IRI-2016 model for all hours of the day except during the post-midnight hours. Slight
post-noon peaks in the daytime maximum and post-sunset decrease and
enhancement are observed in the diurnal variation in OBS-TEC during the
equinoxes. On a seasonal scale, we observed that OBS-TEC values were higher
in the equinoxes than the solstices only in 2012. However, in 2011, the September
equinox and December solstice recorded a higher magnitude, followed by the March
equinox, and the magnitude was lowest in the June solstice. In 2013, the December solstice magnitude
was highest, followed by the equinoxes, and it was lowest in the June solstice. In 2014,
the March equinox and December solstice magnitudes were higher than the September
equinox and June solstice magnitude. The June solstice consistently recorded the
lowest values for all the years. OBS-TEC is found to increase from 2011 to
2014, thus revealing solar cycle dependence.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.