In the solar wind, CMEs manifest as magnetic clouds. Even for CMEs with a well-defined acceleration stage, the pre-acceleration stage is often absent, or perhaps unobservable. Some balloon CMEs, usually the slowest ones, lack this three-stage evolution, instead accelerating slowly and continuously throughout their flight. These values are also lower limits because ejections propagating away from Earth (backside CMEs) usually cannot be detected by coronagraphs.Ĭurrent knowledge of CME kinematics indicates that the ejection starts with an initial pre-acceleration phase characterized by a slow rising motion, followed by a period of rapid acceleration away from the Sun until a near-constant velocity is reached. The frequency of ejections depends on the phase of the solar cycle: from about 0.2 per day near the solar minimum to 3.5 per day near the solar maximum. However, the estimated mass values for CMEs are only lower limits, because coronagraph measurements provide only two-dimensional data. These speeds correspond to transit times from the Sun out to the mean radius of Earth's orbit of about 13 hours to 86 days (extremes), with about 3.5 days as the average. ĬMEs reach velocities from 20 to 3,200 km/s (12 to 1,988 mi/s) with an average speed of 489 km/s (304 mi/s), based on SOHO/ LASCO measurements between 19. During solar maximum, they originate from active regions whose latitudinal distribution is more homogeneous. During solar minimum, CMEs form primarily in the coronal streamer belt near the solar magnetic equator. However, CMEs may also be initiated in quiet surface regions, although in many cases the quiet region was recently active. These field lines must be broken or weakened for the ejection to escape from the Sun. These regions have closed magnetic field lines, in which the magnetic field strength is large enough to contain the plasma. Most ejections originate from active regions on the Sun's surface, such as groupings of sunspots associated with frequent flares. However, some CMEs exhibit more complex geometry. The dense core is usually interpreted as a prominence embedded in the CME (see § Eruptive prominences) with the leading edge as an area of compressed plasma ahead of the CME flux rope. A typical CME may have any or all of three distinctive features: a dense core, a surrounding cavity of low electron density, and a bright leading edge. This magnetic field is commonly in the form of a flux rope, a helical magnetic field with changing pitch angles.ĬMEs can typically be observed in white-light coronagraphs via Thomson scattering of sunlight off of free electrons within the CME plasma. The ejected matter is a plasma consisting primarily of electrons and protons embedded within the ejected magnetic field. Ī video of a series of filament and prominence eruptions during solar cycle 24.ĬMEs release large quantities of matter and magnetic flux away from the Sun's atmosphere and into the solar wind and interplanetary space. Near solar maxima, the Sun produces about three CMEs every day, whereas near solar minima, there is about one CME every five days. Also known as the Carrington Event, it disabled parts of the at the time newly created United States telegraph network, starting fires and shocking some telegraph operators. The largest recorded geomagnetic perturbation, resulting presumably from a CME, was the solar storm of 1859. 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. If a CME enters interplanetary space, it is referred to as an interplanetary coronal mass ejection ( ICME). 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. A coronal mass ejection ( CME) is a significant release of plasma and accompanying magnetic field from the Sun's corona into the solar wind.
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