What cause the sunstorm?

That's a relative term. It is called a sunstorm on earth because sometimes the electro magnetic forces can wreak havoc in electrical systems and other things. A sunstorm is merely the energy fluctuations of the sun in it's strongest emissions. The sun is basically a huge, gigantic ball of fire. Fire is constantly in motion and it's output fluctuates wildly. The surface of the sun is a fire and long arms of fire and electric pulses are coming off the sun all the time. When the long arms of fire are particularly long, sunstorms occur.