This video shows the particle flow around Earth as solar ejecta associated with a coronal mass ejection strike.
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.
Coronal mass ejections are often associated with other forms of solar activity, 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.
Description
Follow a CME as it passes Venus then Earth, and explore how the Sun drives Earth's winds and oceans.
Arcs rise above an active region on the surface of the Sun.
Coronal mass ejections are associated with enormous changes and disturbances in the coronal magnetic field. They are usually observed with a white-light coronagraph.
Cause
Scientific research has shown that the phenomenon of magnetic reconnection is closely associated with CMEs and solar flares. In magnetohydrodynamic theory, the sudden rearrangement of magnetic field lines when two oppositely directed magnetic fields are brought together is called "magnetic reconnection". Reconnection releases energy stored in the original stressed magnetic fields. These magnetic field lines can become twisted in a helical structure, with a 'right-hand twist' or a 'left hand twist'. As the Sun's magnetic field lines become more and more twisted, CMEs appear to be a 'valve' to release the magnetic energy being built up, as evidenced by the helical structure of CMEs, that would otherwise renew itself continuously each solar cycle and eventually rip the Sun apart.On the Sun, magnetic reconnection may happen on solar arcades—a series of closely occurring loops of magnetic lines of force. These lines of force quickly reconnect into a low arcade of loops, leaving a helix of magnetic field unconnected to the rest of the arcade. The sudden release of energy during this process causes the solar flare and ejects the CME. The helical magnetic field and the material that it contains may violently expand outwards forming a CME. This also explains why CMEs and solar flares typically erupt from what are known as the active regions on the Sun where magnetic fields are much stronger on average.
Impact on Earth
When the ejection is directed towards Earth and reaches it as an interplanetary CME (ICME), the shock wave of traveling mass causes a geomagnetic storm that may disrupt Earth's magnetosphere, compressing it on the day side and extending the night-side magnetic tail. When the magnetosphere reconnects on the nightside, it releases power on the order of terawatt scale, which is directed back toward Earth's upper atmosphere.Solar energetic particles can cause particularly strong aurorae in large regions around Earth's magnetic poles. These are also known as the Northern Lights (aurora borealis) in the northern hemisphere, and the Southern Lights (aurora australis) in the southern hemisphere. Coronal mass ejections, along with solar flares of other origin, can disrupt radio transmissions and cause damage to satellites and electrical transmission line facilities, resulting in potentially massive and long-lasting power outages.
Energetic protons released by a CME can cause an increase in the number of free electrons in the ionosphere, especially in the high-latitude polar regions. The increase in free electrons can enhance radio wave absorption, especially within the D-region of the ionosphere, leading to Polar Cap Absorption (PCA) events.
Humans at high altitudes, as in airplanes or space stations, risk exposure to relatively intense solar particle events. The energy absorbed by astronauts is not reduced by a typical spacecraft shield design and, if any protection is provided, it would result from changes in the microscopic inhomogeneity of the energy absorption events.
Physical properties
A video of the series of CMEs in August 2010.
This
video features two model runs. One looks at a moderate coronal mass
ejection (CME) from 2006. The second run examines the consequences of a
large coronal mass ejection, such as the Carrington-class CME of 1859.
Most ejections originate from active regions on the Sun's surface, such as groupings of sunspots associated with frequent flares. These regions have closed magnetic field lines, in which the magnetic field strength is large enough to contain the plasma. These field lines must be broken or weakened for the ejection to escape from the Sun. However, CMEs may also be initiated in quiet surface regions, although in many cases the quiet region was recently active. During solar minimum, CMEs form primarily in the coronal streamer belt near the solar magnetic equator. During solar maximum, they originate from active regions whose latitudinal distribution is more homogeneous.
Coronal mass ejections 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 1996 and 2003. 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. 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. The frequency of ejections depends on the phase of the solar cycle: from about one every fifth day near the solar minimum to 3.5 per day near the solar maximum. These values are also lower limits because ejections propagating away from Earth (backside CMEs) usually cannot be detected by coronagraphs.
Current knowledge of coronal mass ejection 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. Some balloon CMEs, usually the slowest ones, lack this three-stage evolution, instead accelerating slowly and continuously throughout their flight. Even for CMEs with a well-defined acceleration stage, the pre-acceleration stage is often absent, or perhaps unobservable.
Association with other solar phenomena
Video of a solar filament being launched
Coronal mass ejections are often associated with other forms of solar activity, most notably:
- Solar flares
- Eruptive prominence and X-ray sigmoids[13]
- Coronal dimming (long-term brightness decrease on the solar surface)
- Moreton waves
- Coronal waves (bright fronts propagating from the location of the eruption)
- Post-eruptive arcades
Theoretical models
It was first postulated that CMEs might be driven by the heat of an explosive flare. However, it soon became apparent that many CMEs were not associated with flares, and that even those that were often started before the flare. Because CMEs are initiated in the solar corona (which is dominated by magnetic energy), their energy source must be magnetic.Because the energy of CMEs is so high, it is unlikely that their energy could be directly driven by emerging magnetic fields in the photosphere (although this is still a possibility). Therefore, most models of CMEs assume that the energy is stored up in the coronal magnetic field over a long period of time and then suddenly released by some instability or a loss of equilibrium in the field. There is still no consensus on which of these release mechanisms is correct, and observations are not currently able to constrain these models very well. These same considerations apply equally well to solar flares, but the observable signatures of these phenomena differ.
Interplanetary coronal mass ejections
Illustration of a coronal mass ejection moving beyond the planets toward the heliopause
CMEs typically reach Earth one to five days after leaving the Sun. During their propagation, CMEs interact with the solar wind and the interplanetary magnetic field (IMF). As a consequence, slow CMEs are accelerated toward the speed of the solar wind and fast CMEs are decelerated toward the speed of the solar wind. The strongest deceleration or acceleration occurs close to the Sun, but it can continue even beyond Earth orbit (1 AU), which was observed using measurements at Mars and by the Ulysses spacecraft. CMEs faster than about 500 km/s (310 mi/s) eventually drive a shock wave. This happens when the speed of the CME in the frame of reference moving with the solar wind is faster than the local fast magnetosonic speed. Such shocks have been observed directly by coronagraphs in the corona, and are related to type II radio bursts. They are thought to form sometimes as low as 2 Rs (solar radii). They are also closely linked with the acceleration of solar energetic particles.
Related solar observation missions
NASA mission Wind
On 1 November 1994, NASA launched the Wind spacecraft as a solar wind monitor to orbit Earth's L1 Lagrange point as the interplanetary component of the Global Geospace Science (GGS) Program within the International Solar Terrestrial Physics (ISTP) program. The spacecraft is a spin axis-stabilized satellite that carries eight instruments measuring solar wind particles from thermal to >MeV energies, electromagnetic radiation from DC to 13 MHz radio waves, and gamma-rays. Though the Wind spacecraft is over two decades old, it still provides the highest time, angular, and energy resolution of any of the solar wind monitors. It continues to produce relevant research as its data has contributed to over 150 publications since 2008 alone.NASA mission STEREO
On 25 October 2006, NASA launched STEREO, two near-identical spacecraft which, from widely separated points in their orbits, are able to produce the first stereoscopic images of CMEs and other solar activity measurements. The spacecraft orbit the Sun at distances similar to that of Earth, with one slightly ahead of Earth and the other trailing. Their separation gradually increased so that after four years they were almost diametrically opposite each other in orbit.NASA mission Parker Solar Probe
The Parker Solar Probe was launched on 12 August 2018 to measure the mechanisms which accelerate and transport energetic particles i.e. the origins of the solar wind.History
First traces
The largest recorded geomagnetic perturbation, resulting presumably from a CME, coincided with the first-observed solar flare on 1 September 1859. The resulting solar storm of 1859 is now referred to as the Carrington Event, The flare and the associated sunspots were visible to the naked eye (both as the flare itself appearing on a projection of the Sun on a screen and as an aggregate brightening of the solar disc), and the flare was independently observed by English astronomers R. C. Carrington and R. Hodgson. The geomagnetic storm was observed with the recording magnetograph at Kew Gardens. The same instrument recorded a crochet, an instantaneous perturbation of Earth's ionosphere by ionizing soft X-rays. This could not easily be understood at the time because it predated the discovery of X-rays by Röntgen and the recognition of the ionosphere by Kennelly and Heaviside. The storm took down parts of the recently created US telegraph network, starting fires and shocking some telegraph operators.Historical records were collected and new observations recorded in annual summaries by the Astronomical Society of the Pacific between 1953 and 1960.
First clear detections
The first detection of a CME as such was made on 14 December 1971, by R. Tousey (1973) of the Naval Research Laboratory using the seventh Orbiting Solar Observatory (OSO-7).[24] The discovery image (256 × 256 pixels) was collected on a Secondary Electron Conduction (SEC) vidicon tube, transferred to the instrument computer after being digitized to 7 bits. Then it was compressed using a simple run-length encoding scheme and sent down to the ground at 200 bit/s. A full, uncompressed image would take 44 minutes to send down to the ground. The telemetry was sent to ground support equipment (GSE) which built up the image onto Polaroid print. David Roberts, an electronics technician working for NRL who had been responsible for the testing of the SEC-vidicon camera, was in charge of day-to-day operations. He thought that his camera had failed because certain areas of the image were much brighter than normal. But on the next image the bright area had moved away from the Sun and he immediately recognized this as being unusual and took it to his supervisor, Dr. Guenter Brueckner, and then to the solar physics branch head, Dr. Tousey. Earlier observations of coronal transients or even phenomena observed visually during solar eclipses are now understood as essentially the same thing.1989-present
On 9 March 1989 a coronal mass ejection occurred. On 13 March 1989 a severe geomagnetic storm struck the Earth. It caused power failures in Quebec, Canada and short-wave radio interference.On 1 August 2010, during solar cycle 24, scientists at the Harvard–Smithsonian Center for Astrophysics (CfA) observed a series of four large CMEs emanating from the Earth-facing hemisphere of the Sun. The initial CME was generated by an eruption on 1 August that was associated with NOAA Active Region 1092, which was large enough to be seen without the aid of a solar telescope. The event produced significant aurorae on Earth three days later.
On 23 July 2012, a massive, and potentially damaging, solar superstorm (solar flare, CME, solar EMP) barely missed Earth, according to NASA.
On 31 August 2012 a CME connected with Earth's magnetic environment, or magnetosphere, with a glancing blow causing aurora to appear on the night of 3 September.[28][29] Geomagnetic storming reached the G2 (Kp=6) level on NOAA's Space Weather Prediction Center scale of geomagnetic disturbances.
14 October 2014 ICME was photographed by the Sun-watching spacecraft PROBA2 (ESA), Solar and Heliospheric Observatory (ESA/NASA), and Solar Dynamics Observatory (NASA) as it left the Sun, and STEREO-A observed its effects directly at 1 AU. ESA's Venus Express gathered data. The CME reached Mars on 17 October and was observed by the Mars Express, MAVEN, Mars Odyssey, and Mars Science Laboratory missions. On 22 October, at 3.1 AU, it reached comet 67P/Churyumov–Gerasimenko, perfectly aligned with the Sun and Mars, and was observed by Rosetta. On 12 November, at 9.9 AU, it was observed by Cassini at Saturn. The New Horizons spacecraft was at 31.6 AU approaching Pluto when the CME passed three months after the initial eruption, and it may be detectable in the data. Voyager 2 has data that can be interpreted as the passing of the CME, 17 months after. The Curiosity rover's RAD instrument, Mars Odyssey, Rosetta and Cassini showed a sudden decrease in galactic cosmic rays (Forbush decrease) as the CME's protective bubble passed by.
Future risk
According to a report published in 2012 by physicist Pete Riley of Predictive Science Inc., the chance of Earth being hit by a Carrington-class storm between 2012 and 2022 is 12%.Stellar coronal mass ejections
There have been a small number of CMEs observed on other stars, all of which as of 2016 have been found on M dwarfs. These have been detected by spectroscopy, most often by studying Balmer lines: the material ejected toward the observer causes asymmetry in the blue wing of the line profiles due to Doppler shift. This enhancement can be seen in absorption when it occurs on the stellar disc (the material is cooler than its surrounding), and in emission when it is outside the disc. The observed projected velocities of CMEs range from ≈84 to 5,800 km/s (52 to 3,600 mi/s). Compared to activity on the Sun, CME activity on other stars seems to be far less common.Solar storm of 1859
Sunspots of September 1, 1859, as sketched by Richard Carrington.
A and B mark the initial positions of an intensely bright event, which
moved over the course of five minutes to C and D before disappearing.
The solar storm of 1859 (also known as the Carrington Event) was a powerful geomagnetic solar storm during solar cycle 10 (1855–1867). A solar coronal mass ejection (CME) hit Earth's magnetosphere and induced one of the largest geomagnetic storms on record, September 1–2, 1859. The associated "white light flare" in the solar photosphere was observed and recorded by British astronomers Richard C. Carrington (1826–1875) and Richard Hodgson (1804–1872). The now-standard unique IAU identifier for this flare is SOL1859-09-01.
A solar storm of this magnitude occurring today would cause widespread disruptions and damage due to extended outages of the electrical grid. The solar storm of 2012 was of similar magnitude, but it passed Earth's orbit without striking the planet.
Carrington flare
From August 28 to September 2, 1859, many sunspots appeared on the Sun. On August 29, southern auroras were observed as far north as Queensland, Australia. Just before noon on September 1, the English amateur astronomers Richard Carrington and Richard Hodgson independently made the first observations of a solar flare.[6] Carrington and Hodgson compiled independent reports which were published side-by-side in the Monthly Notices of the Royal Astronomical Society, and exhibited their drawings of the event at the November 1859 meeting of the Royal Astronomical Society.The flare was associated with a major coronal mass ejection (CME) that travelled directly toward Earth, taking 17.6 hours to make the 150 million kilometre (93 million mile) journey. It is believed that the relatively high speed of this CME (typical CMEs take several days to arrive at Earth) was made possible by a prior CME, perhaps the cause of the large aurora event on August 29 that "cleared the way" of ambient solar wind plasma for the Carrington event.
Because of a geomagnetic solar flare effect ("magnetic crochet") observed in the Kew Observatory magnetometer record by Scottish physicist Balfour Stewart and a geomagnetic storm observed the following day, Carrington suspected a solar-terrestrial connection. Worldwide reports on the effects of the geomagnetic storm of 1859 were compiled and published by American mathematician Elias Loomis, which support the observations of Carrington and Stewart.
On September 1–2, 1859, one of the largest recorded geomagnetic storms (as recorded by ground-based magnetometers) occurred. Auroras were seen around the world, those in the northern hemisphere as far south as the Caribbean; those over the Rocky Mountains in the U.S. were so bright that the glow woke gold miners, who began preparing breakfast because they thought it was morning. People in the northeastern United States could read a newspaper by the aurora's light. The aurora was visible as far from the poles as south-central Mexico, Queensland, Cuba, Hawaii, southern Japan and China, and even at lower latitudes very close to the equator, such as in Colombia. Estimates of the storm strength range from −800 nT to −1750 nT.
Telegraph systems all over Europe and North America failed, in some cases giving telegraph operators electric shocks. Telegraph pylons threw sparks. Some telegraph operators could continue to send and receive messages despite having disconnected their power supplies.
On Saturday, September 3, 1859, the Baltimore American and Commercial Advertiser reported:
Those who happened to be out late on Thursday night had an opportunity of witnessing another magnificent display of the auroral lights. The phenomenon was very similar to the display on Sunday night, though at times the light was, if possible, more brilliant, and the prismatic hues more varied and gorgeous. The light appeared to cover the whole firmament, apparently like a luminous cloud, through which the stars of the larger magnitude indistinctly shone. The light was greater than that of the moon at its full, but had an indescribable softness and delicacy that seemed to envelop everything upon which it rested. Between 12 and 1 o'clock, when the display was at its full brilliancy, the quiet streets of the city resting under this strange light, presented a beautiful as well as singular appearance.In 1909, an Australian gold miner C.F. Herbert retold his observations in a letter to The Daily News in Perth:
I was gold-digging at Rokewood, about four miles from Rokewood township (Victoria). Myself and two mates looking out of the tent saw a great reflection in the southern heavens at about 7 o'clock p.m., and in about half an hour, a scene of almost unspeakable beauty presented itself, lights of every imaginable color were issuing from the southern heavens, one color fading away only to give place to another if possible more beautiful than the last, the streams mounting to the zenith, but always becoming a rich purple when reaching there, and always curling round, leaving a clear strip of sky, which may be described as four fingers held at arm's length. The northern side from the zenith was also illuminated with beautiful colors, always curling round at the zenith, but were considered to be merely a reproduction of the southern display, as all colors south and north always corresponded. It was a sight never to be forgotten, and was considered at the time to be the greatest aurora recorded... The rationalist and pantheist saw nature in her most exquisite robes, recognising, the divine immanence, immutable law, cause, and effect. The superstitious and the fanatical had dire forebodings, and thought it a foreshadowing of Armageddon and final dissolution.In June 2013, a joint venture from researchers at Lloyd's of London and Atmospheric and Environmental Research (AER) in the United States used data from the Carrington Event to estimate the current cost of a similar event to the U.S. alone at $0.6–2.6 trillion.
Other evidence and similar events
Ice cores containing thin nitrate-rich layers have been analysed to reconstruct a history of past solar storms predating reliable observations. Researchers state that data from Greenland ice cores show evidence of individual solar-proton events, including the Carrington event. More recent work by the ice core community shows that nitrate spikes are not a result of solar energetic particle events, and, indeed, no consistency is found in cores from Greenland and Antarctica, and nitrate events can be due to terrestrial events, such as burnings, so use of this technique is in doubt.Less severe storms have occurred in 1921 and 1960, when widespread radio disruption was reported. The March 1989 geomagnetic storm knocked out power across large sections of Quebec. On July 23, 2012 a "Carrington-class" solar superstorm (solar flare, coronal mass ejection, solar EMP) was observed; its trajectory missed Earth in orbit. Information about these observations was first shared publicly by NASA on April 28, 2014.
