Coronal mass ejection

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.[1][2][3]

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.[4]

This video shows the particle flow around Earth as solar ejecta associated with a coronal mass ejection strike.

Description

Follow a CME as it passes Venus then Earth, and explore how the Sun drives Earth's winds and oceans.
Coronal Mass Ejection
Arcs rise above an active region on the surface of the Sun.

Coronal mass ejections release large quantities of matter and electromagnetic radiation into space above the Sun's surface, either near the corona (sometimes called a solar prominence), or farther into the planetary system, or beyond (interplanetary CME). The ejected material is a magnetized plasma consisting primarily of electrons and protons. While solar flares are very fast (being electromagnetic radiation), CMEs are relatively slow.[5]

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

The phenomenon of magnetic reconnection is closely associated with CMEs and solar flares.[6][7] 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.[8]

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.[9] 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.

Auroras over North America
Satellite photo of aurora borealis stretching across Quebec and Ontario in the early morning of 8 October 2012.

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.[10][11]

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.

A typical coronal mass ejection may have any or all of three distinctive features: a cavity of low electron density, a dense core (the prominence, which appears on coronagraph images as a bright region embedded in this cavity), and a bright leading edge.

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.[12] 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

The association of a CME with some of those phenomena is common but not fully understood. For example, CMEs and flares are normally closely related, but there was confusion about this point caused by the events originating beyond the limb. For such events no flare could be detected. Most weak flares do not have associated CMEs; most powerful ones do. Some CMEs occur without any flare-like manifestation, but these are the weaker and slower ones.[14] It is now thought that CMEs and associated flares are caused by a common event (the CME peak acceleration and the flare impulsive phase generally coincide). In general, all of these events (including the CME) are thought to be the result of a large-scale restructuring of the magnetic field; the presence or absence of a CME during one of these restructures would reflect the coronal environment of the process (i.e., can the eruption be confined by overlying magnetic structure, or will it simply break through and enter the solar wind).

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

Coronal mass ejection moving toward heliopause
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.[15] 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[16] and by the Ulysses spacecraft.[17] CMEs faster than about 500 km/s (310 mi/s) eventually drive a shock wave.[18] 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[19] 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.[20]

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.[21][22]

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.[11]

Historical records were collected and new observations recorded in annual summaries by the Astronomical Society of the Pacific between 1953 and 1960.[23]

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,[25] 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) occurred but missed Earth[26][27], an event that many scientists consider to be Carrington-class event.

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.[30][31]

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 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.[32][33]

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%.[26][34]

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.[35] 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.[36] 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).[37][38] Compared to activity on the Sun, CME activity on other stars seems to be far less common.[36][39]

See also

References

  1. ^ Christian, Eric R. (5 March 2012). "Coronal Mass Ejections". NASA/Goddard Space Flight Center. Retrieved 9 July 2013.
  2. ^ Hathaway, David H. (14 August 2014). "Coronal Mass Ejections". NASA/Marshall Space Flight Center. Retrieved 7 July 2016.
  3. ^ "Coronal Mass Ejections". NOAA/Space Weather Prediction Center. Retrieved 7 July 2016.
  4. ^ Fox, Nicky. "Coronal Mass Ejections". NASA/International Solar-Terrestrial Physics. Retrieved 6 April 2011.
  5. ^ Gleber, Max (21 September 2014). "CME Week: The Difference Between Flares and CMEs". NASA. Retrieved 7 July 2016.
  6. ^ "Scientists unlock the secrets of exploding plasma clouds on the sun". Eurekalert.org. American Physical Society. 8 November 2010. Retrieved 7 July 2016.
  7. ^ Phillips, Tony, ed. (1 March 2001). "Cannibal Coronal Mass Ejections". Science News. NASA. Retrieved 20 March 2015.
  8. ^ Green, Lucie (2014). 15 Million Degrees. Viking. p. 212. ISBN 0-670-92218-8.
  9. ^ Holman, Gordon D. (April 2006). "The Mysterious Origins of Solar Flares". Scientific American. 294 (4): 38–45. Bibcode:2006SciAm.294d..38H. doi:10.1038/scientificamerican0406-38. PMID 16596878.
  10. ^ Baker, Daniel N.; et al. (2008). Severe Space Weather Events—Understanding Societal and Economic Impacts: A Workshop Report. National Academies Press. p. 77. doi:10.17226/12507. ISBN 978-0-309-12769-1. These assessments indicate that severe geomagnetic storms pose a risk for long-term outages to major portions of the North American grid. John Kappenman remarked that the analysis shows "not only the potential for large-scale blackouts but, more troubling, ... the potential for permanent damage that could lead to extraordinarily long restoration times."
  11. ^ a b Morring, Jr., Frank (14 January 2013). "Major Solar Event Could Devastate Power Grid". Aviation Week & Space Technology. pp. 49–50. But the most serious potential for damage rests with the transformers that maintain the proper voltage for efficient transmission of electricity through the grid.
  12. ^ Carroll, Bradley W.; Ostlie, Dale A. (2007). An Introduction to Modern Astrophysics. San Francisco: Addison-Wesley. p. 390. ISBN 0-8053-0402-9.
  13. ^ Tomczak, M.; Chmielewska, E. (March 2012). "A Catalog of Solar X-Ray Plasma Ejections Observed by the Soft X-Ray Telescope on Board Yohkoh". The Astrophysical Journal Supplement Series. 199 (1). 10. arXiv:1201.1040. Bibcode:2012ApJS..199...10T. doi:10.1088/0067-0049/199/1/10.
  14. ^ Andrews, M. D. (December 2003). "A Search for CMEs Associated with Big Flares". Solar Physics. 218 (1): 261–279. Bibcode:2003SoPh..218..261A. doi:10.1023/B:SOLA.0000013039.69550.bf.
  15. ^ Manoharan, P. K. (May 2006). "Evolution of Coronal Mass Ejections in the Inner Heliosphere: A Study Using White-Light and Scintillation Images". Solar Physics. 235 (1–2): 345–368. Bibcode:2006SoPh..235..345M. doi:10.1007/s11207-006-0100-y.
  16. ^ Freiherr von Forstner, Johan L.; Guo, Jingnan; Wimmer-Schweingruber, Robert F.; et al. (January 2018). "Using Forbush Decreases to Derive the Transit Time of ICMEs Propagating from 1 AU to Mars". Journal of Geophysical Research: Space Physics. 123 (1): 39–56. arXiv:1712.07301. Bibcode:2018JGRA..123...39F. doi:10.1002/2017JA024700.
  17. ^ Richardson, I. G. (October 2014). "Identification of Interplanetary Coronal Mass Ejections at Ulysses Using Multiple Solar Wind Signatures". Solar Physics. 289 (10): 3843–3894. Bibcode:2014SoPh..289.3843R. doi:10.1007/s11207-014-0540-8.
  18. ^ Wilkinson, John (2012). New Eyes on the Sun: A Guide to Satellite Images and Amateur Observation. Springer. p. 98. ISBN 978-3-642-22838-4.
  19. ^ Vourlidas, A.; Wu, S. T.; Wang, A. H.; Subramanian, P.; Howard, R. A. (December 2003). "Direct Detection of a Coronal Mass Ejection-Associated Shock in Large Angle and Spectrometric Coronagraph Experiment White-Light Images". The Astrophysical Journal. 598 (2): 1392–1402. arXiv:astro-ph/0308367. Bibcode:2003ApJ...598.1392V. doi:10.1086/379098.
  20. ^ Manchester, W. B., IV; Gombosi, T. I.; De Zeeuw, D. L.; Sokolov, I. V.; Roussev, I. I.; et al. (April 2005). "Coronal Mass Ejection Shock and Sheath Structures Relevant to Particle Acceleration" (PDF). The Astrophysical Journal. 622 (2): 1225–1239. Bibcode:2005ApJ...622.1225M. doi:10.1086/427768. Archived from the original (PDF) on 5 February 2007.
  21. ^ "Spacecraft go to film Sun in 3D". BBC News. 26 October 2006.
  22. ^ "STEREO". NASA.
  23. ^ Astronomical Society of the Pacific Visual Records
  24. ^ Howard, Russell A. (October 2006). "A Historical Perspective on Coronal Mass Ejections" (PDF). Solar Eruptions and Energetic Particles. Geophysical Monograph Series. 165. American Geophysical Union. Bibcode:2006GMS...165....7H. doi:10.1029/165GM03.
  25. ^ Howard, Russell A. (1999). "Obituary: Guenter E. Brueckner, 1934-1998". Bulletin of the American Astronomical Society. 31 (5): 1596. Bibcode:1999BAAS...31.1596H.
  26. ^ a b Phillips, Tony (23 July 2014). "Near Miss: The Solar Superstorm of July 2012". NASA. Retrieved 26 July 2014.
  27. ^ "ScienceCasts: Carrington-class CME Narrowly Misses Earth". YouTube.com. NASA. 28 April 2014. Retrieved 26 July 2014.
  28. ^ "NASA's SDO Sees Massive Filament Erupt on Sun". NASA. 4 September 2012. Retrieved 11 September 2012.
  29. ^ "August 31, 2012 Magnificent CME". NASA/Goddard Space Flight Center. 31 August 2012. Retrieved 11 September 2012.
  30. ^ "Space Weather Alerts and Warnings Timeline: September 1–16, 2012 (archive)". NOAA. Archived from the original on 28 September 2012. Retrieved 24 September 2012.
  31. ^ Chillymanjaro (6 September 2012). "Geomagnetic storming levels back to normal". The Watchers. Retrieved 11 September 2012.
  32. ^ Witasse, O.; Sánchez-Cano, B.; Mays, M. L.; Kajdič, P.; Opgenoorth, H.; et al. (14 August 2017). "Interplanetary coronal mass ejection observed at STEREO-A, Mars, comet 67P/Churyumov-Gerasimenko, Saturn, and New Horizons en route to Pluto: Comparison of its Forbush decreases at 1.4, 3.1, and 9.9 AU". Journal of Geophysical Research: Space Physics. Bibcode:2017JGRA..122.7865W. doi:10.1002/2017JA023884.
  33. ^ "Tracking a solar eruption through the Solar System". SpaceDaily. 17 August 2017. Retrieved 22 August 2017.
  34. ^ Riley, Pete (February 2012). "On the probability of occurrence of extreme space weather events". Space Weather. American Geophysical Union. 10 (2). Bibcode:2012SpWea..10.2012R. doi:10.1029/2011SW000734.
  35. ^ Korhonen, Heidi; Vida, Krisztian; Leitzinger, Martin; et al. (20 December 2016). "Hunting for Stellar Coronal Mass Ejections". arXiv:1612.06643 [astro-ph.SR].
  36. ^ a b Vida, K.; Kriskovics, L.; Oláh, K.; et al. (May 2016). "Investigating magnetic activity in very stable stellar magnetic fields. Long-term photometric and spectroscopic study of the fully convective M4 dwarf V374 Pegasi". Astronomy & Astrophysics. 590. A11. arXiv:1603.00867. Bibcode:2016A&A...590A..11V. doi:10.1051/0004-6361/201527925.
  37. ^ Leitzinger, M.; Odert, P.; Ribas, I.; et al. (December 2011). "Search for indications of stellar mass ejections using FUV spectra". Astronomy & Astrophysics. 536. A62. Bibcode:2011A&A...536A..62L. doi:10.1051/0004-6361/201015985.
  38. ^ Houdebine, E. R.; Foing, B. H.; Rodonò, M. (November 1990). "Dynamics of flares on late-type dMe stars: I. Flare mass ejections and stellar evolution". Astronomy & Astrophysics. 238 (1–2): 249–255. Bibcode:1990A&A...238..249H.
  39. ^ Leitzinger, M.; Odert, P.; Greimel, R.; et al. (September 2014). "A search for flares and mass ejections on young late-type stars in the open cluster Blanco-1". Monthly Notices of the Royal Astronomical Society. 443 (1): 898–910. arXiv:1406.2734. Bibcode:2014MNRAS.443..898L. doi:10.1093/mnras/stu1161.

Further reading

Books
  • Gopalswamy, Natchimuthukonar; Mewaldt, Richard A.; Torsti, Jarmo, eds. (2006). Solar Eruptions and Energetic Particles. Geophysical Monograph Series. 165. American Geophysical Union. Bibcode:2006GMS...165.....G. doi:10.1029/GM165. ISBN 0-87590-430-0.
Internet articles

External links

AR12665

AR12665 was a 75,000 mile active region of the Sun's surface. It was active in July 2017, and is notable for the images produced by a NASA satellite. The active region contained "several solar flares, a coronal mass ejection and a solar energetic particle event."

Bastille Day event

The Bastille Day Flare or Bastille Day Event was a powerful solar flare on July 14, 2000, the national day of France, occurring near the peak of the solar maximum in solar cycle 23. The X5.7-class flare originated from a sunspot known as Active region 9077, which subsequently caused an S3 radiation storm on Earth fifteen minutes later as energetic protons bombarded the ionosphere. It was the biggest solar radiation event since 1989. The proton event was four times more intense than any previously recorded since the launches of SOHO in 1995 and ACE in 1997. The flare was also followed by a full-halo coronal mass ejection and a geomagnetic super storm on July 15–16. The geomagnetic storm peaked at the extreme level, G5, in the late hours of July 15.

Despite their great distance from the Sun, the Bastille Day event was observed by Voyager 1 and Voyager 2.

C/2002 V1 (NEAT)

Comet C/2002 V1 (NEAT) is a non-periodic comet that appeared in November 2002. The comet peaked with an apparent magnitude of approximately –0.5, making it the eighth-brightest comet seen since 1935. It was seen by SOHO in February 2003. At perihelion the comet was only 0.099258 astronomical units (14,848,800 kilometres; 9,226,600 miles) from the Sun. (Slight controversy arose when the comet failed to break up when it approached the Sun, as expected by some scientists if it were a small comet.)The comet was hit by a coronal mass ejection during its pass near the Sun; some rumoured it had "disturbed" the Sun, but scientists dismissed this notion. The scientific consensus is that there is no link between comets and CMEs that can not be explained through simple coincidence, and there were 56 CMEs in February 2003. On February 18, 2003, comet C/2002 V1 (NEAT) passed 5.7 degrees from the Sun. C/2002 V1 (NEAT) appeared impressive as viewed by the Solar and Heliospheric Observatory (SOHO) as a result of the forward scattering of light off of the dust in the coma and tail. After the comet left LASCO's field of view, on February 20, 2003, an object was seen at the bottom of a single frame. Although technicians dismissed this as a software bug, rumours persisted that the object had been expelled from the Sun.

The orbit of a long-period comet is properly obtained when the osculating orbit is computed at an epoch after leaving the planetary region and is calculated with respect to the center of mass of the solar system. Using JPL Horizons, the barycentric orbital elements for epoch 2020-Jan-01 generate a semi-major axis of 1,100 AU, an apoapsis distance of 2,230 AU, and a period of approximately 37,000 years.

Coronal cloud

A coronal cloud is the cloud of hot plasma gas surrounding a coronal mass ejection. It is usually made up of protons and electrons. When a coronal mass ejection occurs at the Earth's Sun, it is the coronal cloud that usually reaches Earth and causes damage to electrical equipment and space satellites, not the ejection or flare itself. The damage is mostly the result of the high amount of electricity moving through the atmosphere.A coronal cloud is released when a solar flare becomes a coronal mass ejection; the coronal cloud often contains more radioactive particles than the mass ejection itself. A coronal mass ejection occurs when a solar flare becomes so hot that it snaps and breaks in two, becoming a "rope" of heat and magnetism that stretches between two sunspots. The resulting coronal mass ejection can be compared to a horseshoe magnet, the sunspots being the poles and the oscillating magnetic connector the handle. Coronal mass ejections typically do not last very long, because they cool down as the coronal cloud of gas is released and begins to hurtle away from the Sun.

Cosmic storm

Cosmic storm may refer to:

Cosmic ray burst

Geomagnetic storm, the interaction of the Sun's outburst with Earth's magnetic field

Interacting galaxies

Coronal mass ejection

Solar flare

Nebula

Forbush decrease

A Forbush decrease is a rapid decrease in the observed galactic cosmic ray intensity following a coronal mass ejection (CME). It occurs due to the magnetic field of the plasma solar wind sweeping some of the galactic cosmic rays away from Earth. The term Forbush decrease was named after the American physicist Scott E. Forbush, who studied cosmic rays in the 1930s and 1940s.

Lagrange (spacecraft)

Lagrange is a 2018 concept study for a solar weather mission by the European Space Agency (ESA). This is a British-led concept that envisions two spacecraft to be positioned at Lagrangian points L1 and L5.Monitoring space weather includes events such as solar flares, coronal mass ejections,

geomagnetic storms, solar proton events, etc. Monitoring would help predict arrival times at the Earth and any potential effect on infrastructure. If funded, both Lagrange missions would launch in the 2020s.

List of articles related to the Sun

Articles related to the Sun include:

Corona

Solar wind

Coronal mass ejection

Solar eclipse

total eclipse

annular eclipse

hybrid eclipse

partial eclipse

Magnitude of eclipse

Saros (astronomy)

Sunspot, where most solar flares and coronal mass ejections originate

Wolf number, counts sunspots

Maunder Minimum, the period roughly spanning 1645 to 1715 when sunspots became exceedingly rare

Solar flare

Solar cycle, periodic change in the amount of irradiation from the Sun that is experienced on Earth

List of solar cycles

Solar maximum - large numbers of sunspots appear

Solar minimum - sunspot and solar flare activity diminishes

Homeric Minimum

Dalton Minimum, lasting from about 1790 to 1830

Modern Maximum, period of relatively high solar activity that began circa 1900

Solar variation, change in the amount of solar radiation emitted

Solar System

Solar and celestial effects on climate (Earth's climate, that is)

List of coronal mass ejections

The following contains a list of coronal mass ejections. A coronal mass ejection (CME) is a massive burst of solar wind and magnetic fields rising above the solar corona or being released into space. Most ejections originate from active regions on the Sun's surface, such as groupings of sunspots associated with frequent flares.

Magnetic cloud

A magnetic cloud is a transient event observed in the solar wind. It was defined in 1981 by Burlaga et al. 1981 as a region of enhanced magnetic field strength, smooth rotation of the magnetic field vector, and low proton temperature. Magnetic clouds are a possible manifestation of a coronal mass ejection (CME). The association between CMEs and magnetic clouds was made by Burlaga et al. in 1982 when a magnetic cloud was observed by Helios-1 two days after being observed by SMM. However, because observations near Earth are usually done by a single spacecraft, many CMEs are not seen as being associated with magnetic clouds. The typical structure observed for a fast CME by a satellite such as ACE is a fast-mode shock wave followed by a dense (and hot) sheath of plasma (the downstream region of the shock) and a magnetic cloud.

May 1921 geomagnetic storm

The May 1921 geomagnetic storm was a significant event caused by the impact of an extraordinarily powerful coronal mass ejection on Earth's magnetosphere. It took place on 13 through 15 May, and was part of solar cycle 15. This event occurred before extensive interconnectivity of electrical systems and the general electrical dependency across infrastructures in the developed world, so the effect was restricted to certain sectors, even though resulting ground currents were up to an order of magnitude greater than those of the March 1989 geomagnetic storm that blacked out large parts of northeastern North America. At the time, scientists gave the size of the sunspot that began on May 10th and caused the storm as 94,000 by 21,000 miles (131,000 km by 33,800 km) in size.Northern lights appeared in much of the eastern United States, creating brightly lit night skies. Telegraph service in the United States was slowed and then virtually eliminated around midnight of the 14th due to blown fuses, and damaged equipment. On the other hand, radio waves were strengthened during the storm due to ionosphere activation, allowing for some strong intercontinental reception. Electric lights did not seem to have been noticeably affected. Undersea cables also suffered from the storm. Damage to telegraph systems were also reported in Europe

and the southern hemisphere.

Moreton wave

A Moreton wave or Moreton-Ramsey wave is the chromospheric signature of a large-scale solar coronal shock wave. Described as a kind of solar "tsunami", they are generated by solar flares. They are named for American astronomer Gail Moreton, an observer at the Lockheed Solar Observatory in Burbank, and Harry E. Ramsey, an observer who spotted them in 1959 at The Sacramento Peak Observatory. He discovered them in time-lapse photography of the chromosphere in the light of the Balmer alpha transition.

There were few follow-up studies for decades. Then the 1995 launch of the Solar and Heliospheric Observatory led to observation of coronal waves, which cause Moreton waves. Moreton waves were a research topic again. (SOHO's EIT instrument discovered another, different wave type called "EIT waves".)

The reality of Moreton waves (a.k.a. fast-mode MHD waves) has also been confirmed by the two STEREO spacecraft. They observed a 100,000-km-high wave of hot plasma and magnetism, moving at 250 km/s, in conjunction with a big coronal mass ejection in February 2009.

Moreton measured the waves propagating at a speed of 500–1500 km/s. Yutaka Uchida interpreted Moreton waves as MHD fast mode shock waves propagating in the corona. He links them to type II radio bursts, which are radio-wave discharges created when coronal mass ejections accelerate shocks.Moreton waves can be observed primarily in the Hα band.

Solar eclipse of July 18, 1860

A total solar eclipse occurred on July 18, 1860. A solar eclipse occurs when the Moon passes between Earth and the Sun, thereby totally or partly obscuring the image of the Sun for a viewer on Earth. A total solar eclipse occurs when the Moon's apparent diameter is larger than the Sun's, blocking all direct sunlight, turning day into darkness. Totality occurs in a narrow path across Earth's surface, with the partial solar eclipse visible over a surrounding region thousands of kilometres wide.

People watching an eclipse in 1860 at Toulouse, France. Picture by Eugène Trutat, Muséum de Toulouse.

Solar flare

A solar flare is a sudden flash of increased brightness on the Sun, usually observed near its surface

and in close proximity to a sunspot group.

Powerful flares are often, but not always, accompanied by a coronal mass ejection. Even the most powerful flares are barely detectable in the total solar irradiance (the "solar constant").Solar flares occur in a power-law spectrum of magnitudes; an energy release of typically 1020 joules of energy suffices to produce a clearly observable event, while a major event can emit up to 1025 joules.Flares are closely associated with the ejection of plasmas and particles through the Sun's corona into outer space; flares also copiously emit radio waves.

If the ejection is in the direction of the Earth, particles associated with this disturbance can penetrate into the upper atmosphere (the ionosphere) and cause bright auroras, and may even disrupt long range radio communication.

It usually takes days for the solar plasma ejecta to reach Earth. Flares also occur on other stars, where the term stellar flare applies.

High-energy particles, which may be relativistic, can arrive almost simultaneously with the electromagnetic radiations.

On July 23, 2012, a massive, potentially damaging, solar storm (solar flare, coronal mass ejection and electromagnetic radiation) barely missed Earth. According to NASA, there may be as much as a 12% chance of a similar event occurring between 2012 and 2022.

Solar phenomena

Solar phenomena are the natural phenomena occurring within the magnetically heated outer atmospheres in the Sun. These phenomena take many forms, including solar wind, radio wave flux, energy bursts such as solar flares, coronal mass ejection or solar eruptions, coronal heating and sunspots.

These phenomena are apparently generated by a helical dynamo near the center of the Sun's mass that generates strong magnetic fields and a chaotic dynamo near the surface that generates smaller magnetic field fluctuations.The total sum of all solar fluctuations is referred to as solar variation. The collective effect of all solar variations within the Sun's gravitational field is referred to as space weather. A major weather component is the solar wind, a stream of plasma released from the Sun's upper atmosphere. It is responsible for the aurora, natural light displays in the sky in the Arctic and Antarctic. Space weather disturbances can cause solar storms on Earth, disrupting communications, as well as geomagnetic storms in Earth's magnetosphere and sudden ionospheric disturbances in the ionosphere. Variations in solar intensity also affect Earth's climate. These variations can explain events such as ice ages and the Great Oxygenation Event, while the Sun's future expansion into a red giant will likely end life on Earth.

Solar activity and related events have been recorded since the 8th century BCE. Babylonians inscribed and possibly predicted solar eclipses, while the earliest extant report of sunspots dates back to the Chinese Book of Changes, c.  800 BCE. The first extant description of the solar corona was in 968, while the earliest sunspot drawing was in 1128 and a solar prominence was described in 1185 in the Russian Chronicle of Novgorod. The invention of the telescope allowed major advances in understanding, allowing the first detailed observations in the 1600s. Solar spectroscopy began in the 1800s, from which properties of the solar atmosphere could be determined, while the creation of daguerreotypy led to the first solar photographs on 2 April 1845. Photography assisted in the study of solar prominences, granulation and spectroscopy. Early in the 20th century, interest in astrophysics surged in America. A number of new observatories were built with solar telescopes around the world. The 1931 invention of the coronagraph allowed the corona to be studied in full daylight.

Solar storm of 1859

The solar storm of 1859 (also known as the Carrington Event) was a powerful geomagnetic 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 electrical disruptions, blackouts 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, missing by nine days.

Solar storm of 2012

The solar storm of 2012 was an unusually large and strong coronal mass ejection (CME) event that occurred on July 23 that year. It missed the Earth with a margin of approximately nine days, as the equator of the Sun rotates around its own axis with a period of about 25 days. The region that produced the outburst was thus not pointed directly towards the Earth at that time. The strength of the eruption was comparable to the 1859 Carrington event that caused damage to electric equipment worldwide, which at that time consisted mostly of telegraph stations.The eruption tore through Earth's orbit, hitting the STEREO-A spacecraft. The spacecraft is a solar observatory equipped to measure such activity, and because it was far away from the Earth and thus not exposed to the strong electrical currents that can be induced when a CME hits the Earth's magnetosphere, it survived the encounter and provided researchers with valuable data.

Based on the collected data, the eruption consisted of two separate ejections which were able to reach exceptionally high strength as the interplanetary medium around the Sun had been cleared by a smaller CME four days earlier. Had the CME hit the Earth, it is likely that it would have inflicted serious damage to electronic systems on a global scale. A 2013 study estimated that the economic cost to the United States would have been between $0.6 and 2.6 trillion USD. Ying D. Liu, professor at China's State Key Laboratory of Space Weather, estimated that the recovery time from such a disaster would have been about four to ten years.The record fastest CME associated with the solar storm of August 1972 is thought to have occurred in a similar process of earlier CMEs clearing particles in the path to Earth. This storm arrived in 14.6 hours, an even shorter duration after the parent flare erupted than for the great solar storm of 1859.

The event occurred at a time of high sunspot activity during Solar cycle 24.

Solar wind

The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma consists of mostly electrons, protons and alpha particles with kinetic energy between 0.5 and 10 keV. Embedded within the solar-wind plasma is the interplanetary magnetic field. The solar wind varies in density, temperature and speed over time and over solar latitude and longitude. Its particles can escape the Sun's gravity because of their high energy resulting from the high temperature of the corona, which in turn is a result of the coronal magnetic field.

At a distance of more than a few solar radii from the Sun, the solar wind is supersonic and reaches speeds of 250 to 750 kilometers per second. The flow of the solar wind is no longer supersonic at the termination shock. The Voyager 2 spacecraft crossed the shock more than five times between 30 August and 10 December 2007. Voyager 2 crossed the shock about a billion kilometers closer to the Sun than the 13.5-billion-kilometer distance where Voyager 1 came upon the termination shock. The spacecraft moved outward through the termination shock into the heliosheath and onward toward the interstellar medium. Other related phenomena include the aurora (northern and southern lights), the plasma tails of comets that always point away from the Sun, and geomagnetic storms that can change the direction of magnetic field lines.

Stellar mass loss

Stellar mass loss is a phenomenon observed in some massive stars. It occurs when a triggering event causes the ejection of a large portion of the star's mass. Stellar mass loss can also occur when a star gradually loses material to a binary companion or into interstellar space.

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