Coronal-mass ejections are associated with flares and filaments. CMEs pack the most powerful punch a solar storm can deliver. The largest of these can send more than 1 billion tons of protons and electrons racing from the sun at speeds of more than 4 million miles an hour. The intensity of the effect they have on Earth depends on the location of the source region on the sun as well as on how strongly the cloud's magnetic field couples to that of Earth as it arrives. The stronger the coupling, the more intense the geomagnetic storm. As the CME travels, it plows through the sun's slower-moving solar wind, creating a shock wave that can turbocharge protons, generating a radiation storm. When it reaches Earth, a CME can trigger an initial, intense geomagnetic storm, followed by a few days of continued disturbance of varying intensity. Effects range from brighter auroras and surges along power grids and long-distance pipelines to intense radiation storms and severely disrupted radio communications in polar regions. During CMEs, airlines reroute fights that ordinarily use polar routes to maintain radio communications for transcontinental flights.