Not to be confused with a solar flare, a CME is a solar phenomenon that can send solar particles into space and reach Earth one to three days later.
Earth-directed CMEs can cause a space weather phenomenon called a geomagnetic storm, which occurs when they connect with the outside of the Earth's magnetic envelope, the magnetosphere, for an extended period of time. In the past, CME's such as this have caused auroras near the poles but didn't disrupt electrical systems on Earth or interfere with GPS or satellite-based communications systems.
Among the SOHO instruments is the Michelson Doppler Interferometer (MDI) and the Extreme ultraviolet Imaging Telescope (EIT).