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The signal amplitude of 22.1 kHz Very Low Frequency (VLF) waves, transmitted from the radio station Skelton, UK (GQD at 54.70 N, 2.80 W) and received at South France station (SID, Sudden Ionospheric Disturbance monitoring station at 460N, 20E) is studied for the effect of geomagnetic storms on the lower ionosphere. The VLF parameters, D-Layer Preparation Time (DLPT) depth and Mid-Day Peak (MDP) have been used to study the response of D-region to the geomagnetic storms occurred during the equinox months of 2012-2015. The two parameters recorded enhancement on the storm day and subsequent days. A shift in the sunrise Terminator Time is observed for the geomagnetic storms for which Sudden Commencement (SC) occurred during the day lit hours on the previous day. The observed effect of the geomagnetic storms on the mid latitude D-region is due to the precipitation of high energy particles. The response of F2-region to geomagnetic storms is studied using the foF2 data at Dourbes (50.10 N, 4.60 E), Belgium which is near the mid-point of the GQD-South France VLF path. The percentage of deviation of foF2 from the quiet day values, DfoF2 is found to undergo positive and negative changes. The positive storm effect during daytime is mainly due to the penetration electric field and strong negative phase during both day time and night time is due to depleted [O]/[N2] ratios.
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