Alec

Yes, there's evidence that lightning activity is surprisingly strongly influenced by the sun's magnetic field polarity, with observational data identifying that lightning flashes were up to twice as frequent over the UK when the sun's magnetic field was pointing towards the Earth compared to when it pointed away. Of course, the magnetic field can't generate the storms themselves (that's left to it's visible spectrum!) but the change in field seems to promote electrification of existing storms or at least help their discharge through lightning. The physical mechanism for this is still unknown, but may be due to the influence of high energy particles altering the environment of the upper portion of the cloud. If you're interested you can check out this link to a recent research papers for more info from a UK perspective: http://iopscience.iop.org/article/10.1088/1748-9326/9/11/115009/meta http://onlinelibrary.wiley.com/doi/10.1002/2015GL066802/abstract

Elevated storms can indeed produce intense lightning activity, but I don't think it is for the reasons you suggest. Cloud charging and lightning initiation is still an active area of research, but recent studies from the US indicate that the important aspect is the amount of water content reaching an altitude where temperatures are below freezing (the mixed phase region of the cloud), since it is the interaction of ice particles of different sizes in the updraft which produces strong electrical charging. For a given updraft speed, an elevated cloud base helps this charging since there is less water condensing below the freezing level, which can be removed as rainfall instead of supplying the mixed phase region. Additionally, the higher cloud base promotes broader updrafts with less entrainment of ambient air, allowing more water to reach the mixed phase region thereby producing more ice for charging. Whilst some of the cloud's charge is lost through charge transfer back to ground on falling precipitation particles (the "precipitation current"), lightning is often concentrated around heavy convective rain cores since this is usually near to where the greatest updrafts are found and therefore the strongest charged regions within the cloud. Raindrops no not alter the ambient electric field or air electrical conductivity through dissipation; air conductivity is instead determined by the amount of ions available, with liquid and ice particles implicated as a possible source of lightning initiation due to the enhanced electric field surrounding them. Hope this is of interest!