Effects of thunderstorms on the lower ionosphere as observed by VLF radio signals

Abstract:

We present the lower ionospheric disturbances due to the pre-monsoon summer thunderstorms over Kolkata, India using Very Low Frequency (VLF) radio receivers. In general, individual lightning can perturb the upper mesosphere and lower ionosphere in many ways. Ionospheric perturbations due to lightning are observed regularly as disturbances in the VLF radio signals, propagating within the earth-ionosphere waveguide, in a time scale ranging from few milliseconds to few tens of seconds. Here, we have focused on the cumulative effects or the total effects of the mesoscale thunderstorm system over the lower ionosphere. We have found several cases in 2019 where radio signals showed significant disturbances associated with severe thunderstorms. The disturbance patterns are highly correlated with the lightning flash rate graphs estimated from the Earth Networks Lightning data. We have estimated the changes in ionospheric conductivity profile associated with the events. Thus our observations indicate that conductivity of the upper mesosphere and lower ionosphere (UMLI) above a severe thunderstorm get affected during the whole thunderstorm period. The reason could be linked with either due to the electromagnetic pulse field or due to heating effect of lightning.