Been living in Southern California for over a decade and we do not really have lighting or thunder here. It is very weak. Grew up in the Mid West and have seen some big lighting storms. The storm I drove through was in Texas (where else) and appeared to be right where the Dry Southwest climate bordered up against the Wet Southeast climate. Was right between San Antonio and Houston on the 10.
So you may not need a major astro physical event to kick these big lightning storms off. Possible that any major change in climatic conditions could help increase the charge potentials. Right now the sun is at about 40 sunspots (just below average). Granted it was active for a couple of months earlier in the year. Possible too that low activity allows more cosmic rays and those rays can also increase charge potentials or affect plasma.
And it should be noted that the sun can discharge large CME's even when activity is weak or average.
Keep in mind that these plasma instabilities 1. are generally not seen in lightning and 2. that the carvings are nearly all oriented to have been done by a viewer looking toward the south pole, 3. they’re all over the world and number in the millions, and 4. that their orientation/foreshortening corresponds to a viewpoint by latitude on a global scale. None of the last 3 could be accounted for by a purely local phenomenon.