Abstract:
Initial results of subionospheric very low frequency (VLF) perturbations observed on NWC (19.8 kHz) and NPM (21.4 kHz) transmitter signals at low latitude ground station Varanasi, India, during the period January–June 2010, are presented. Characteristics and occurrence rates of these events mainly observed during nighttime are studied. Most of the early VLF events had slow recovery with amplitude perturbations of 0.5–4.5 dB and phase changes of 3–12°. Temporal variation of the events is studied. World Wide Lightning Location Network data along with the broadband VLF data are analyzed to find the location of causative lightning discharge and/or the sferics associated with these early VLF events. Lightning induced changes in D-region ionospheric conductivity are attributed to the perturbations in the VLF signals.
