This informative paper is by; Ching-Cheh Hung, National Aeronautics and Space Administration, Glenn Research Center, Cleveland, Ohio 44135.
Extract from Summary; A solar storm is a storm of ions and electrons from the Sun. Large solar storms are usually preceded by solar flares, phenomena that can be characterized quantitatively from Earth. Twenty-five of the thirtyeight largest known solar flares were observed to start when one or more tide-producing planets
(Mercury, Venus, Earth, and Jupiter) were either nearly above the event positions (<10° longitude) or at the opposing side of the Sun. The probability for this to happen at random is 0.039 percent. Download 1.7MB pdf of paper