Understanding Space Weather: Part II: The Violent Sun

Abstract

Abstract The Sun is often racked by short-term violent events such as flares and coronal mass ejections (CMEs) but these two phenomena are often confused. Both are caused by the release of energy due to the reconnection of stressed and unstable magnetic fields. Flares bathe the solar system in electromagnetic radiation from gamma rays to radio emissions. CMEs throw billions of tons of solar plasma into interplanetary space at velocities of over 1,000 km s−1. Flares can occur without significant ejecta being spewed out from the Sun into the solar system. CMEs can occur without a significant flare being detected. The most violent and dangerous events occur when a large flare is accompanied by a major eruption. These violent events are much more common near solar maximum but can occur at any time during the solar cycle, so we are rarely completely immune to their effects. Various types of solar activity can lead to problems with electrical grids, navigation systems, and communications, and can present a hazard to astronauts, as will be discussed in future papers in this series.