A particle storm is a caused by solar energetic particles (SEPs).
SEPs created by solar flares and CMEs are very energetic bursts of particles that pose a major threat to the electronics and power systems of satellites. The Earth’s atmosphere is normally a very good shield against energetic particles but during the strongest of these events particles can disrupt electronics in airplanes and even electronics on the ground. These particles can pose a significant health risk to airline crew and passengers. Particle storms can create the same atmospheric absorption effects as solar flares causing HF blackouts near the poles.