Editing Solar cycle (section)

== Solar dynamo ==
{{Technical|section|date=April 2025}}
{{Main|Solar dynamo}}

The 11-year solar cycle is thought to be one-half of a 22-year [[Babcock Model|Babcock–Leighton solar dynamo cycle]], which corresponds to an oscillatory exchange of energy between [[toroidal and poloidal]] solar magnetic fields which is mediated by solar plasma flows which also provides energy to the dynamo system at every step. At [[Solar maximum|solar-cycle maximum]], the external poloidal dipolar magnetic field is near its dynamo-cycle minimum strength, but an internal [[Toroidal and poloidal|toroidal]] quadrupolar field, generated through differential rotation within the [[tachocline]], is near its maximum strength. At this point in the dynamo cycle, buoyant upwelling within the [[Convection zone]] forces emergence of the toroidal magnetic field through the photosphere, giving rise to pairs of sunspots, roughly aligned east–west with opposite magnetic polarities. The magnetic polarity of sunspot pairs alternates every solar cycle, a phenomenon described by [[Hale's law]].<ref>{{Cite journal |last1=Hale |first1=G. E. |last2=Ellerman |first2=F. |last3= Nicholson |first3=S. B. |last4=Joy |first4=A. H. |title=The Magnetic Polarity of Sun-Spots |journal=The Astrophysical Journal |volume=49 |page=153 |year=1919 |doi=10.1086/142452 |bibcode=1919ApJ....49..153H}}</ref><ref name="solarcycle">{{cite news |date=4 January 2008 |title=NASA Satellites Capture Start of New Solar Cycle |work=[[PhysOrg]] |url=http://www.physorg.com/news119271347.html |access-date=10 July 2009}}</ref>

During the solar cycle's declining phase, energy shifts from the internal toroidal magnetic field to the external poloidal field, and sunspots diminish in number. At solar minimum, the toroidal field is, correspondingly, at minimum strength, sunspots are relatively rare and the poloidal field is at maximum strength. During the next cycle, differential rotation converts magnetic energy back from the poloidal to the toroidal field, with a polarity that is opposite to the previous cycle. The process carries on continuously, and in an idealized, simplified scenario, each 11-year sunspot cycle corresponds to a change in the polarity of the Sun's large-scale magnetic field.<ref>{{Cite news
 |date=16 February 2001
 |title=Sun flips magnetic field
 |url=http://archives.cnn.com/2001/TECH/space/02/16/sun.flips/index.html
 |archive-url=https://web.archive.org/web/20051115051328/http://archives.cnn.com/2001/TECH/space/02/16/sun.flips/index.html
 |archive-date=15 November 2005
 |work=[[CNN]]
 |access-date=11 July 2009
}}http://www.cnn.com/2001/TECH/space/02/16/sun.flips/index.html</ref><ref>{{cite web
 |last=Phillips
 |first=T.
 |date=15 February 2001
 |title=The Sun Does a Flip
 |url=https://science.nasa.gov/headlines/y2001/ast15feb_1.htm
 |archive-url=https://web.archive.org/web/20011104023531/https://science.nasa.gov/headlines/y2001/ast15feb_1.htm
 |archive-date=4 November 2001
 |publisher=[[NASA]]
 |access-date=11 July 2009
}}</ref>

Solar dynamo models indicate that plasma flux transport processes in the solar interior such as differential rotation, meridional circulation and turbulent pumping play an important role in the recycling of the toroidal and poloidal components of the solar magnetic field.<ref>{{cite journal |last1=Hazra |first1=Soumitra |last2=Nandy |first2=Dibyendu |date=2016 |title=A Proposed Paradigm for Solar Activity Dynamics Mediated via Turbulent Pumping of Magnetic Flux in Babcock-Leighton-type Solar Dynamics |journal=The Astrophysical Journal |volume=832 |issue=1 |at=9 |doi=10.3847/0004-637X/832/1/9 |doi-access=free|arxiv=1608.08167 }}</ref> The relative strengths of these flux transport processes also determine the "memory" of the solar cycle that plays an important role in physics-based predictions of the solar cycle. In particular, stochastically forced non-linear solar dynamo simulations establish that the solar cycle memory is short, lasting over one cycle, thus implying accurate predictions are possible only for the next solar cycle and not beyond.<ref>{{cite journal |last1=Yeates |first1=Anthony R. |last2=Nandy |first2=Dibyendu |last3=Mackay |first3=Duncan H. |date=2008 |title=Exploring the Physical Basis of Solar Cycle Predictions: Flux Transport Dynamics and Persistence of Memory in Advection- versus Diffusion-dominated Solar Convection Zones |journal=The Astrophysical Journal |volume=673 |issue=1 |at=544 |doi=10.1086/524352 |doi-access=free|arxiv=0709.1046 |bibcode=2008ApJ...673..544Y }}</ref><ref>{{cite journal |last1=Karak |first1=Bidya Binay |last2=Nandy |first2=Dibyendu |date=2012 |title=Turbulent Pumping of Magnetic Flux Reduxes Solar Cycle Memory and thus Impacts Predictability of the Sun's Activity |journal=The Astrophysical Journal |volume=761 |issue=1 |at=L13 |doi=10.1088/2041-8205/761/1/L13 |doi-access=free|arxiv=1206.2106 |bibcode=2012ApJ...761L..13K }}</ref> This postulate of a short one cycle memory in the solar dynamo mechanism was later observationally verified.<ref>{{cite journal |title=Solar Cycle Propagation, Memory, and Prediction: Insights from a century of magnetic proxies |last1=Muñoz-Jaramillo |first1=Andrés |last2=Dasi-Espuig |first2=María |last3=Balmaceda |first3=Laura A. |last4=DeLuca |first4=Edward E. |date=2013 |journal=The Astrophysical Journal Letters |volume=767 |issue=2 |at=L25 |doi=10.1088/2041-8205/767/2/L25 |doi-access=free|arxiv=1304.3151 |bibcode=2013ApJ...767L..25M }}</ref>

Although the [[tachocline]] has long been thought to be the key to generating the Sun's large-scale magnetic field, recent research has questioned this assumption. Radio observations of [[brown dwarfs]] have indicated that they also maintain large-scale magnetic fields and may display cycles of magnetic activity. The Sun has a radiative core surrounded by a convective envelope, and at the boundary of these two is the [[tachocline]]. However, brown dwarfs lack radiative cores and tachoclines. Their structure consists of a solar-like convective envelope that exists from core to surface. Since they lack a [[tachocline]] yet still display solar-like magnetic activity, it has been suggested that solar magnetic activity is only generated in the convective envelope.<ref>{{cite journal |last1=Route |first1=Matthew |title=The Discovery of Solar-like Activity Cycles Beyond the End of the Main Sequence? |journal=The Astrophysical Journal Letters |date=October 20, 2016 |volume=830 |issue=2 |page=27 |arxiv=1609.07761 |bibcode=2016ApJ...830L..27R |s2cid=119111063 |doi=10.3847/2041-8205/830/2/L27 |doi-access=free}}</ref>