Editing Solar cycle (section)

== Phenomena ==
{{Main|Solar phenomena}} Because the solar cycle reflects magnetic activity, various magnetically driven solar phenomena follow the solar cycle, including sunspots, faculae/plage, network, and coronal mass ejections.

=== Sunspots ===
{{Main|Sunspot}}
[[File:ChroniclesofJohnofWorcester.jpg|thumb|upright=1.15|A [[Sunspot drawing|drawing of a sunspot]] in the Chronicles of [[John of Worcester]], ca. 1100<ref>{{Cite web |url=https://sunearthday.nasa.gov/2006/locations/firstdrawing.php |title=NASA – Sun-Earth Day – Technology Through Time – Greece |website=sunearthday.nasa.gov}}</ref>]]
The Sun's apparent surface, the photosphere, radiates more actively when there are more sunspots. Satellite monitoring of [[solar luminosity]] revealed a direct relationship between the solar cycle and luminosity with a peak-to-peak amplitude of about 0.1%.<ref name="Willson91">{{cite journal |last = Willson|first = Richard C.|author2 = H.S. Hudson|year = 1991|title = The Sun's luminosity over a complete solar cycle|journal = Nature|volume = 351|issue = 6321|pages = 42–4|doi = 10.1038/351042a0|bibcode = 1991Natur.351...42W|s2cid = 4273483}}<!-- {{harvnb|Willson|1991}} --></ref> Luminosity decreases by as much as 0.3% on a 10-day timescale when large groups of sunspots rotate across the Earth's view and increase by as much as 0.05% for up to 6 months due to [[Solar facula|faculae]] associated with large sunspot groups.<ref name="Willson81">{{Cite journal |vauthors=Willson RC, Gulkis S, Janssen M, Hudson HS, Chapman GA |title = Observations of Solar Irradiance Variability|journal = Science|volume = 211|issue = 4483|pages = 700–2|date = February 1981|pmid = 17776650|doi = 10.1126/science.211.4483.700|bibcode = 1981Sci...211..700W}}</ref>

The best information today comes from [[Solar and Heliospheric Observatory|SOHO]] (a cooperative project of the [[European Space Agency]] and [[NASA]]), such as the MDI [[Solar magnetogram|magnetogram]], where the solar "surface" [[magnetic field]] can be seen.

As each cycle begins, sunspots appear at mid-latitudes, and then move closer and closer to the equator until a solar minimum is reached. This pattern is best visualized in the form of the so-called butterfly diagram. Images of the Sun are divided into latitudinal strips, and the monthly-averaged fractional surface of sunspots is calculated. This is plotted vertically as a color-coded bar, and the process is repeated month after month to produce this time-series diagram.
[[File:Sun - btly - 2023.png|center|thumb|upright=2.5|This version of the sunspot butterfly diagram was constructed by the solar group at NASA Marshall Space Flight Center. The newest version can be found at [http://solarcyclescience.com/solarcycle.html solarcyclescience.com]]]
While magnetic field changes are concentrated at sunspots, the entire Sun undergoes analogous changes, albeit of smaller magnitude.
[[File:LAMF - 2023.png|center|thumb|upright=2.5|Time vs. solar latitude diagram of the radial component of the solar magnetic field, averaged over successive solar rotation. The "butterfly" signature of sunspots is clearly visible at low latitudes. Diagram constructed by the solar group at NASA Marshall Space Flight Center. The newest version can be found at [http://solarcyclescience.com/solarcycle.html solarcyclescience.com]]]

=== Faculae and plage ===
{{Main|Solar facula|Solar plage}}
[[File:Plage areas chatzistergos 2020.png|thumb|upright=1.35|Solar plage area evolution over time]]
Faculae are bright magnetic features on the photosphere. They extend into the chromosphere, where they are referred to as plage. The evolution of plage areas is typically tracked from solar observations in the Ca II K line (393.37&nbsp;nm).<ref>{{Cite journal |last1=Chatzistergos |first1=Theodosios |last2=Krivova |first2=Natalie A. |last3=Ermolli |first3=Ilaria |date=2022-11-17 |title=Full-disc Ca ii K observations—A window to past solar magnetism |journal=Frontiers in Astronomy and Space Sciences |volume=9 |page=1038949 |doi=10.3389/fspas.2022.1038949 |arxiv=2210.13285 |bibcode=2022FrASS...938949C |issn=2296-987X|doi-access=free }}</ref> The amount of facula and plage area varies in phase with the solar cycle, and they are more abundant than sunspots by approximately an order of magnitude.<ref name="Chatzistergos2020">{{Cite journal |vauthors=Chatzistergos T, Ermolli I, Krivova NA, Solanki SK, Banerjee D, Barata T, Belik M, et al. |title = Analysis of full-disc Ca II K spectroheliograms – III. Plage area composite series covering 1892–2019|journal = Astronomy and Astrophysics|volume = 639|pages = A88|date = July 2020|doi = 10.1051/0004-6361/202037746| arxiv=2005.01435 |bibcode = 2020A&A...639A..88C| s2cid=218487277 }}</ref> They exhibit a non linear relation to sunspots.<ref>{{Cite journal |last1=Chatzistergos |first1=Theodosios |last2=Ermolli |first2=Ilaria |last3=Krivova |first3=Natalie A. |last4=Barata |first4=Teresa |last5=Carvalho |first5=Sara |last6=Malherbe |first6=Jean-Marie |date=November 2022 |title=Scrutinising the relationship between plage areas and sunspot areas and numbers |url=https://www.aanda.org/10.1051/0004-6361/202244913 |journal=Astronomy & Astrophysics |volume=667 |pages=A167 |doi=10.1051/0004-6361/202244913 |arxiv=2209.07077 |bibcode=2022A&A...667A.167C |s2cid=252280541 |issn=0004-6361}}</ref> Plage regions are also associated with strong magnetic fields in the solar surface.<ref>{{Cite journal |last1=Chatzistergos |first1=Theodosios |last2=Ermolli |first2=Ilaria |last3=Solanki |first3=Sami K. |last4=Krivova |first4=Natalie A. |last5=Giorgi |first5=Fabrizio |last6=Yeo |first6=Kok Leng |date=June 2019 |title=Recovering the unsigned photospheric magnetic field from Ca II K observations |url=https://www.aanda.org/10.1051/0004-6361/201935131 |journal=Astronomy & Astrophysics |volume=626 |pages=A114 |doi=10.1051/0004-6361/201935131 |arxiv=1905.03453 |bibcode=2019A&A...626A.114C |s2cid=148571864 |issn=0004-6361}}</ref><ref>{{Cite journal |last1=Babcock |first1=Horace W. |last2=Babcock |first2=Harold D. |date=March 1955 |title=The Sun's Magnetic Field, 1952–1954. |journal=The Astrophysical Journal |language=en |volume=121 |page=349 |doi=10.1086/145994 |bibcode=1955ApJ...121..349B |issn=0004-637X|doi-access= }}</ref>

=== Solar flares and coronal mass ejections ===
{{Main|Solar flare|Coronal mass ejection}}

The solar magnetic field structures the corona, giving it its characteristic shape visible at times of solar eclipses. Complex coronal magnetic field structures evolve in response to fluid motions at the solar surface, and emergence of [[magnetic flux]] produced by [[solar dynamo|dynamo]] action in the solar interior. For reasons not yet understood in detail, sometimes these structures lose stability, leading to [[solar flare]]s and [[coronal mass ejection]]s (CME). Flares consist of an abrupt emission of energy (primarily at [[ultraviolet]] and [[X-ray]] wavelengths), which may or may not be accompanied by a coronal mass ejection, which consists of injection of energetic particles (primarily ionized hydrogen) into interplanetary space. Flares and CME are caused by sudden localized release of magnetic energy, which drives emission of ultraviolet and X-ray radiation as well as energetic particles. These eruptive phenomena can have a significant impact on Earth's upper atmosphere and space environment, and are the primary drivers of what is now called [[space weather]]. Consequently, the occurrence of both [[geomagnetic storm]]s<ref>{{Cite journal |last1=Owens |first1=Mathew J. |last2=Lockwood |first2=Mike |last3=Barnard |first3=Luke A. |last4=Scott |first4=Chris J. |last5=Haines |first5=Carl |last6=Macneil |first6=Allan |date=2021-05-20 |title=Extreme Space-Weather Events and the Solar Cycle |journal=Solar Physics |language=en |volume=296 |issue=5 |page=82 |doi=10.1007/s11207-021-01831-3 |bibcode=2021SoPh..296...82O |s2cid=236402345 |issn=1573-093X|doi-access=free }}</ref> and [[Solar energetic particles|solar energetic particle]]<ref>{{Cite journal |last1=Owens |first1=Mathew J. |last2=Barnard |first2=Luke A. |last3=Pope |first3=Benjamin J. S. |last4=Lockwood |first4=Mike |last5=Usoskin |first5=Ilya |last6=Asvestari |first6=Eleanna |date=2022-08-19 |title=Solar Energetic-Particle Ground-Level Enhancements and the Solar Cycle |journal=Solar Physics |language=en |volume=297 |issue=8 |page=105 |doi=10.1007/s11207-022-02037-x |arxiv=2207.12787 |bibcode=2022SoPh..297..105O |s2cid=251066764 |issn=1573-093X}}</ref> events shows a strong solar cycle variation, peaking close to sunspot maximum.

The occurrence frequency of coronal mass ejections and flares is strongly modulated by the cycle. Flares of any given size are some 50 times more frequent at solar maximum than at minimum. Large coronal mass ejections occur on average a few times a day at solar maximum, down to one every few days at solar minimum. The size of these events themselves does not depend sensitively on the phase of the solar cycle. A case in point are the three large X-class flares that occurred in December 2006, very near solar minimum; an X9.0 flare on Dec 5 stands as one of the brightest on record.<ref>{{Cite journal
 | title=The Most Powerful Solar Flares Ever Recorded
 | website=Spaceweather.com
 | url=http://www.spaceweather.com/solarflares/topflares.html
 }}</ref>