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Concept
Coronal mass ejection
Summary
A coronal mass ejection (CME) is a significant ejection of magnetic field and accompanying plasma mass from the Sun's corona into the heliosphere. CMEs are often associated with solar flares and other forms of solar activity, but a broadly accepted theoretical understanding of these relationships has not been established.
If a CME enters interplanetary space, it is referred to as an interplanetary coronal mass ejection (ICME). ICMEs are capable of reaching and colliding with Earth's magnetosphere, where they can cause geomagnetic storms, aurorae, and in rare cases damage to electrical power grids. The largest recorded geomagnetic perturbation, resulting presumably from a CME, was the solar storm of 1859. Also known as the Carrington Event, it disabled parts of the newly created United States telegraph network, starting fires and shocking some telegraph operators.
Near solar maxima, the Sun produces about three CMEs every day, whereas near solar minima, there is about one CME every five days.
CMEs release large quantities of matter and magnetic flux from the Sun's atmosphere into the solar wind and interplanetary space. The ejected matter is a plasma consisting primarily of electrons and protons embedded within the ejected magnetic field. This magnetic field is commonly in the form of a flux rope, a helical magnetic field with changing pitch angles.
The average mass ejected is . However, the estimated mass values for CMEs are only lower limits, because coronagraph measurements provide only two-dimensional data.
CMEs erupt from strongly twisted or sheared, large-scale magnetic field structures in the corona that are kept in equilibrium by overlying magnetic fields.
CMEs erupt from the lower corona, where processes associated with the local magnetic field dominate over other processes. As a result, the coronal magnetic field plays an important role in the formation and eruption of CMEs. Pre-eruption structures originate from magnetic fields that are initially generated in the Sun's interior by the solar dynamo.
Official source
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