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.
Energetic particles and electromagnetic radiation (EM) from solar events and galactic cosmic rays can bombard and interact with satellites' exposed surfaces, and sometimes possess enough energy to penetrate their surface. Among other known effects, the scenario can cause accelerated orbit decay due to atmospheric drag, sporadic and unexplainable errors in functions of sensitive parts, degradation of critical properties of structural materials, jeopardy of flight worthiness, transient and terminal health hazard to both onboard passengers and astronauts, and sometimes a catastrophic failure that can abruptly end satellite mission. The understanding of the dynamics of the space radiation environment and associated effects is critically important for satellites design and operation in ionospheric plasma environment, in which satellites are designed to function. In this chapter we review some satellite anomalies associated with the space radiation environment and conclude with mitigation effort that can reduce such impact.
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