Editing Geomagnetic storm (section)

==Occurrences==
{{further|List of solar storms}}
The first scientific observation of the effects of a geomagnetic storm occurred early in the 19th century: from May 1806 until June 1807, [[Alexander von Humboldt]] recorded the bearing of a [[magnetic compass]] in Berlin. On 21 December 1806, he noticed that his compass had become erratic during a bright [[Aurora (astronomy)|auroral event]].<ref>{{cite web| last =Russell| first =Randy| title =Geomagnetic Storms| website =Windows to the Universe| publisher =National Earth Science Teachers Association| date =March 29, 2010| url =http://www.windows2universe.org/glossary/geomagnetic_storms.html| access-date = 4 August 2013}}</ref>

On September 1–2, 1859, the largest recorded geomagnetic storm occurred. From August 28 until September 2, 1859, numerous [[sunspot]]s and [[solar flare]]s were observed on the Sun, with the largest flare on September 1. This is referred to as the [[solar storm of 1859]] or the [[Carrington Event]]. It can be assumed that a massive [[coronal mass ejection]] was launched from the Sun and reached the Earth within eighteen hours—a trip that normally takes three to four days. The horizontal field was reduced by 1600&nbsp;nT as recorded by the [[Colaba Observatory]]. It is estimated that Dst would have been approximately −1760&nbsp;nT.<ref>{{cite journal | last1 = Tsurutani | first1 = B. T. | last2 = Gonzalez | first2 = W. D. | last3 = Lakhina | first3 = G. S. | last4 = Alex | first4 = S. | year = 2003 | title = The extreme magnetic storm of 1–2 September 1859 | url = https://zenodo.org/record/1000695| journal = J. Geophys. Res. | volume = 108 | issue = A7| page = 1268 | doi = 10.1029/2002JA009504 | bibcode=2003JGRA..108.1268T| doi-access = free }}</ref> [[Aurora (astronomy)#Historically significant events|Telegraph wires]] in both the United States and Europe experienced induced voltage increases ([[Electromotive force|emf]]), in some cases even delivering shocks to telegraph operators and igniting fires. Aurorae were seen as far south as Hawaii, Mexico, Cuba and Italy—phenomena that are usually only visible in polar regions. [[Ice cores]] show evidence that events of similar intensity recur at an average rate of approximately once per 500 years.

Since 1859, less severe storms have occurred, notably the [[aurora of November 17, 1882]] and the [[May 1921 geomagnetic storm]], both with disruption of telegraph service and initiation of fires, and 1960, when widespread radio disruption was reported.<ref name="Odenwald">{{cite journal |title=Bracing the Satellite Infrastructure for a Solar Superstorm |journal=Sci. Am. |url=http://www.sciam.com/article.cfm?id=bracing-for-a-solar-superstorm |archive-url=https://web.archive.org/web/20081117113249/http://www.sciam.com/article.cfm?id=bracing-for-a-solar-superstorm |url-status=dead |archive-date=2008-11-17 }}</ref>

[[File:ExtremeEvent 19890310-00h 19890315-24h.jpg|thumb|upright=1.85|GOES-7 monitors space weather conditions during the Great Geomagnetic storm of March 1989. The Moscow neutron monitor recorded the passage of a CME as a drop in levels known as a [[Forbush decrease]].<ref>{{cite web | title=Extreme Space Weather Events | publisher=[[National Geophysical Data Center]] | url=https://www.ngdc.noaa.gov/sxi/sxi_greatest.html}}</ref>]]

In [[Solar storm of August 1972|early August 1972]], a series of flares and solar storms peaks with a flare estimated around X20 producing the fastest CME transit ever recorded and a severe geomagnetic and proton storm that disrupted terrestrial electrical and communications networks, as well as satellites (at least one made permanently inoperative), and spontaneously detonated numerous U.S. Navy magnetic-influence sea mines in North Vietnam.<ref>{{cite journal |last = Knipp |first = Delores J. |author2 = B. J. Fraser |author3 = M. A. Shea |author-link3=Margaret Shea (scientist)|author4 = D. F. Smart |title = On the Little-Known Consequences of the 4 August 1972 Ultra-Fast Coronal Mass Ejecta: Facts, Commentary and Call to Action |journal = Space Weather |volume = 16 |issue = 11|pages = 1635–1643|date = 2018 |doi = 10.1029/2018SW002024 |doi-access = free |bibcode = 2018SpWea..16.1635K }}</ref>

The [[March 1989 geomagnetic storm]] caused the collapse of the [[Hydro-Québec]] power grid in seconds as equipment protection relays tripped in a cascading sequence.<ref name="cbc.ca"/><ref>{{harvnb|Bolduc|2002}}</ref> Six million people were [[power outage|left without power]] for nine hours. The storm caused auroras as far south as [[Texas]] and [[Florida]].<ref name="Earth dodges magnetic storm"/> The storm causing this event was the result of a coronal mass ejected from the Sun on March 9, 1989.<ref>{{cite journal|title=Geomagnetic Storms Can Threaten Electric Power Grid |journal=Earth in Space |volume=9 |issue=7 |pages=9–11 |date=March 1997 |url=http://www.agu.org/sci_soc/eiskappenman.html |url-status=dead |archive-url=https://web.archive.org/web/20080611174103/http://www.agu.org/sci_soc/eiskappenman.html |archive-date=2008-06-11 }}</ref> The minimum Dst was −589&nbsp;nT.

On July 14, 2000, an X5 class flare erupted (known as the [[Bastille Day event]]) and a coronal mass was launched directly at the Earth. A geomagnetic super storm occurred on July 15–17; the minimum of the Dst index was −301&nbsp;nT. Despite the storm's strength, no power distribution failures were reported.<ref>{{cite conference |title=High-voltage power grid disturbances during geomagnetic storms |last=Stauning |first=P. |book-title=Proceedings of the Second Solar Cycle and Space Weather Euroconference, 24–29 September 2001 |location=Vico Equense, Italy |editor=Huguette Sawaya-Lacoste |id=ESA SP-477 |publisher=Noordwijk: ESA Publications Division |isbn=92-9092-749-6 |date=2002 |pages=521–524}}</ref> The Bastille Day event was observed by ''[[Voyager 1]]'' and ''[[Voyager 2]]'',<ref>{{cite journal | last1 = Webber | first1 = W. R. | last2 = McDonald | first2 = F. B. | last3 = Lockwood | first3 = J. A. | last4 = Heikkila | first4 = B. | year = 2002 | title = The effect of the July 14, 2000 "Bastille Day" solar flare event on >70 MeV galactic cosmic rays observed at V1 and V2 in the distant heliosphere | journal = Geophys. Res. Lett. | volume = 29 | issue = 10| pages = 1377–1380 | doi = 10.1029/2002GL014729 | bibcode=2002GeoRL..29.1377W| doi-access = free }}</ref> thus it is the farthest out in the Solar System that a solar storm has been observed.

Seventeen major flares erupted on the Sun between 19 October and 5 November 2003, including perhaps the most intense flare ever measured on the [[Geostationary Operational Environmental Satellite|GOES]] XRS sensor—a huge X28 flare,<ref>{{cite journal | last1 = Thomson | first1 = N. R. | last2 = Rodger | first2 = C. J. | last3 = Dowden | first3 = R. L. | year = 2004 | title = Ionosphere gives size of greatest solar flare | journal = Geophys. Res. Lett. | volume = 31 | issue = 6| page = L06803 | doi = 10.1029/2003GL019345 | bibcode = 2004GeoRL..31.6803T | doi-access = free }}</ref> resulting in an extreme radio blackout, on 4 November. These flares were associated with CME events that caused three geomagnetic storms between 29 October and 2 November, during which the second and third storms were initiated before the previous storm period had fully recovered. The minimum Dst values were −151, −353 and −383&nbsp;nT. Another storm in this sequence occurred on 4–5 November with a minimum Dst of −69&nbsp;nT. The last geomagnetic storm was weaker than the preceding storms, because the [[active region]] on the Sun had rotated beyond the meridian where the central portion CME created during the flare event passed to the side of the Earth. The whole sequence became known as the [[Halloween Solar Storm]].<ref>{{cite web |url=http://www.swpc.noaa.gov/Services/HalloweenStorms_assessment.pdf |title=Halloween Space Weather Storms of 2003 |access-date=2011-05-17 |url-status=dead |archive-url=https://web.archive.org/web/20110728172705/http://www.swpc.noaa.gov/Services/HalloweenStorms_assessment.pdf |archive-date=2011-07-28 }} Halloween Space Weather Storms of 2003, NOAA Technical Memorandum OAR SEC-88, Space Environment Center, Boulder, Colorado, June 2004</ref> The [[Wide Area Augmentation System]] (WAAS) operated by the [[Federal Aviation Administration]] (FAA) was offline for approximately 30 hours due to the storm.<ref name="nas2008">{{cite report |url=http://www.nap.edu/catalog/12507.html |title=Severe Space Weather Events - Understanding Societal and Economic Impacts – Workshop Report, National Research Council of the National Academies |publisher=The National Academies Press |location=Washington, D. C. |date=2008}}</ref> The Japanese ADEOS-2 satellite was severely damaged and the operation of many other satellites were interrupted due to the storm.<ref>{{cite web |url=https://www.oecd.org/governance/risk/46891645.pdf |title=Geomagnetic Storms |publisher=CENTRA Technology, Inc. |type=report |date=14 January 2011 |archive-url=https://web.archive.org/web/20230529201915/https://www.oecd.org/governance/risk/46891645.pdf |archive-date=2023-05-29 |url-status=dead}} prepared for the Office of Risk Management and Analysis, United States Department of Homeland Security</ref>