Lower Ionospheric Conductivity Modification Above a Thunderstorm Updraught

Lightning has previously been observed to disturb the lower ionosphere. These lightning-induced ionospheric perturbations were observed as disturbances on subionospheric low-frequency radio wave propagation with fast rise times '3 s and gradual recoveries of duration '10 s. Most of these disturbances were observed during night time when ionospheric conditions are most favorable. Here, a daytime perturbation in the lower ionosphere was observed using subionospheric radio remote sensing. The disturbance exhibits a ∼60 s rise time with a gradual recovery of '200 s. No cloud to ground lightning was coincident with the disturbance onset, however, the intracloud lightning activity of a thunderstorm over the radio receiver was seen to increase at the time of the disturbance. Therefore, the observed disturbance is unlikely to be caused by lightning, yet appears to be associated with the thunderstorm. It is proposed that this disturbance is produced by a pronounced increase in updraught strength that produced a significant change in the quasi-static electrification of the thunderstorm. This change in electrification is evident in the increase in the intracloud lightning activity of the thunderstorm. The observation provides further evidence of the ionospheric heating effect of thundercloud charge which has implications for lower atmosphere-ionosphere energy coupling and possibly sprite initiation.