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.
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 1.6×1012 kg (3.5×1012 lb). 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.
The NOAA Space Weather Scales were introduced as a way to communicate to the general public the current and future space weather conditions and their possible effects on people and systems. Many of the SWPC products describe the space environment, but few have described the effects that can be experienced as the result of environmental disturbances. These scales are useful to users of our products and those who are interested in space weather effects. The scales describe the environmental disturbances for three event types: geomagnetic storms, solar radiation storms, and radio blackouts. The scales have numbered levels, analogous to hurricanes, tornadoes, and earthquakes that convey severity. They list possible effects at each level. They also show how often such events happen, and give a measure of the intensity of the physical causes.
Solar Radiation Storms
|Scale||Description||Effect||Physical measure||Average Frequency|
(1 cycle = 11 years)
|R 5||Extreme||HF Radio: Complete HF (high frequency) radio blackout on the entire sunlit side of the Earth lasting for a number of hours. This results in no HF radio contact with mariners and en route aviators in this sector. Navigation: Low-frequency navigation signals used by maritime and general aviation systems experience outages on the sunlit side of the Earth for many hours, causing loss in positioning. Increased satellite navigation errors in positioning for several hours on the sunlit side of Earth, which may spread into the night side.||X20|
(2 x 10-3)
|Less than 1 per cycle|
|R 4||Severe||HF Radio: HF radio communication blackout on most of the sunlit side of Earth for one to two hours. HF radio contact lost during this time. Navigation: Outages of low-frequency navigation signals cause increased error in positioning for one to two hours. Minor disruptions of satellite navigation possible on the sunlit side of Earth.||X10|
|8 per cycle|
(8 days per cycle)
|R 3||Strong||HF Radio: Wide area blackout of HF radio communication, loss of radio contact for about an hour on sunlit side of Earth. Navigation: Low-frequency navigation signals degraded for about an hour.||X1|
|175 per cycle|
(140 days per cycle)
|R 2||Moderate||HF Radio: Limited blackout of HF radio communication on sunlit side, loss of radio contact for tens of minutes. Navigation: Degradation of low-frequency navigation signals for tens of minutes.||M5|
(5 x 10-5)
|350 per cycle|
(300 days per cycle)
|R 1||Minor||HF Radio: Weak or minor degradation of HF radio communication on sunlit side, occasional loss of radio contact. Navigation: Low-frequency navigation signals degraded for brief intervals.||M1|
|2000 per cycle|
(950 days per cycle)