Influence of lightning on electron density variation in the ionosphere using WWLLN lightning data and GPS data

Includes bibliography.In this study we have demonstrated that a seasonal and diurnal correlation exists between occurrence frequencies of wave-like structures in the form of Traveling Ionospheric Disturbances (TID) in the ionosphere and tropospheric lightning in the mid-latitude region over South Africa. Lightning induced changes in total electron content (TEC) are strongest between September and March, with the more-pronounced effects occurring 12:00 - 22:00 UT, but from April through August there is a low probability of having significant lightning-induced TID occurrence. The strongest oscillations in the total electron content of the ionosphere have dominant periods of range 0.6 to 0.8 and 1.2to 2.5 hours, typical periods for medium scale TIDs and large scale TIDs respectively. Since ionospheric scintillation is caused by irregularities in electron density which act as wave scatterers, it is feasible that lightning-induced TIDs may provide the mechanism for causing the concomitant and co-located changes in ionospheric total electron con-tent that was observed. Both the lightning and the ionospheric irregularity have spatial dependence over South Africa dominating around Bloemfontein. We have also found a strong seasonal and diurnal correlation between occurrence frequencies of the high rate of change of TEC index (ROTI _ 0.8 TECU/min) as a proxy for amplitude scintillationS4 index and lighting stroke rate. The correlation coefficient linking diurnal lightning stroke rate and high ROTI is found to be about 86%. While the seasonal correlation between the monthly average ROTI and average stroke rate is about 70%, the seasonal average ROTI and average stroke rate correlation is found to be about 84%. This there-fore implies that the presence of lightning is a likely cause of the generation of TIDs and subsequent irregularities in the ionosphere