https://www.thunderbolts.info/wp/2014/11/25/lightning-in-the-wind-2/
Electric fields freely accelerate charged particles, which move outward  in opposite directions, activating an electric current that follows the  Sun’s magnetic field. That field is carried into Earth’s electrical  environment along gigantic Birkeland current filaments. It was reported  elsewhere that in September 2002 a major premise of Electric Universe  theory was confirmed: weather systems on Earth are electrically  connected to a field of charged particles called the ionosphere. Dual  bands of plasma shining in ultraviolet light were found by the 
IMAGE satellite.  The plasma streams are circling the Earth in opposite directions along  the equator, carrying positive and negative electric charges.
Along with that observation, the Time History of Events and  Macroscale Interactions during Substorms (THEMIS) satellites found what  were called “space tornadoes” (Birkeland currents), electrified plasma  vortices rotating faster than 1,600,000 kilometers per hour, about  64,000 kilometers from Earth. The THEMIS satellites, together with  Earth-based stations, verified that those charged plasma formations are  connected to the ionosphere. This means that the Sun is directly coupled  to lightning generators on Earth—otherwise called thunderstorms.
 As previously written, the capacitor effect is probably what  contributes to lightning discharges. Capacitors are usually made of two  conductors separated by an insulating medium, or dielectric insulator.  An electric charge on one conductor attracts an opposite charge to the  other conductor, resulting in an electric field between them that acts  as an electrical energy reserve. Thunderstorms are most likely behaving  like capacitors: the clouds are one plate, the ground another, and the  atmosphere is the dielectric insulator.
 Since the clouds are connected to the ionosphere, electric charges  carried into the ionosphere by the solar wind cause increases in the  electrical energy in the clouds, which also increases the stored charge  in the ground. That accumulated charge overcomes the atmosphere’s  ability to keep the two separate, so they reach out to each other in the  form of “leader strokes.” When the two lightning leaders meet, a  circuit between the clouds and the ground (or between one cloud and  another) is completed: lightning flashes.