Coronal Mass Ejection
Introduction
A Coronal Mass Ejection (CME) is a significant release of plasma and accompanying magnetic field from the solar corona. They often follow solar flares and are normally present during a solar prominence eruption. The plasma is released into the solar wind and can be observed in coronagraph imagery.
Characteristics
CMEs are often associated with other forms of solar activity, particularly solar flares, but a broadly accepted theoretical understanding of these relationships has not been established. CMEs most often originate from active regions on the Sun's surface, such as groupings of sunspots associated with frequent flares. Near solar maxima, the Sun produces about three CMEs every day, whereas near solar minima, there is about one CME every five days.
Causes
The exact causes of CMEs are still unclear, but they are believed to be initiated by the loss of equilibrium in the solar magnetic field. In many cases, the structure and dynamics of the outer solar atmosphere, or corona, is dominated by the magnetic field. When a large-scale magnetic structure with twisted field lines (a prominence) becomes unstable, it can lead to a CME.
Impact on Earth
CMEs, along with solar flares, can disrupt radio transmissions, cause power outages (geomagnetic storms), and create auroras (northern and southern lights). They have a number of physical effects on the Earth, such as inducing a ring current in the Earth's magnetosphere, and adding to the radiation environment in near-Earth space. These effects can damage or destroy satellites and disrupt telecommunications and GPS signals.
Detection and Monitoring
CMEs are detected using a variety of instruments, most notably coronagraphs and space-based telescopes. The Solar and Heliospheric Observatory (SOHO) and the Solar Dynamics Observatory (SDO) are among the spacecraft that monitor the Sun to track CMEs and predict their arrival at Earth.