Editing Solar wind (section)

== Properties and structure ==
[[File:52706main hstorion lg.jpg|thumb|This is thought to show the solar wind from the star L.L. Orionis generating a [[bow shock]] (the bright arc).]]

===Fast and slow solar wind===
The solar wind is observed to exist in two fundamental states, termed the slow solar wind and the fast solar wind, though their differences extend well beyond their speeds. In near-Earth space, the slow solar wind is observed to have a velocity of {{val|300|-|500|u=km/s}}, a temperature of ~{{val|100|ul=kilokelvin}} and a composition that is a close match to the [[solar corona|corona]]. By contrast, the fast solar wind has a typical velocity of {{val|750|u=km/s}}, a temperature of {{val|800|u=kilokelvin}}{{Citation needed|reason=The referenced article by Geiss et al 1995 does not provide these numbers|date=July 2024}} and it nearly matches the composition of the Sun's [[photosphere]].<ref>{{Cite journal|last1=Geiss|first1=J.|last2=Gloeckler|first2=G.|last3=Steiger|first3=R. Von|title=Origin of the solar wind from composition data|journal=Space Science Reviews|language=en|volume=72|issue=1–2|pages=49–60|doi=10.1007/BF00768753|issn=0038-6308|bibcode = 1995SSRv...72...49G |year=1995|s2cid=120788623}}</ref> The slow solar wind is twice as dense and more variable in nature than the fast solar wind.<ref name=kallenrode>{{cite book
 | first=May-Britt
 | last=Kallenrode
 | date=2004
 | title=Space Physics: An Introduction to Plasmas and
 | url=https://archive.org/details/springer_10.1007-978-3-662-09959-9
 | publisher=Springer
 | isbn=978-3-540-20617-0 }}</ref><ref>{{cite web
 | last=Suess | first=Steve | date=June 3, 1999
 | url=http://solarscience.msfc.nasa.gov/suess/SolarProbe/Page1.htm
 | title=Overview and Current Knowledge of the Solar Wind and the Corona
 | work=The Solar Probe
 | publisher=NASA/Marshall Space Flight Center
 | access-date=2008-05-07
| url-status=dead |archive-url = https://web.archive.org/web/20080610125820/http://solarscience.msfc.nasa.gov/suess/SolarProbe/Page1.htm <!-- Bot retrieved archive --> |archive-date = 2008-06-10}}</ref>

The slow solar wind appears to originate from a region around the Sun's equatorial belt that is known as the "streamer belt", where coronal streamers are produced by magnetic flux open to the heliosphere draping over closed magnetic loops.{{clarify|date=September 2024}} The exact coronal structures involved in slow solar wind formation and the method by which the material is released is still under debate.<ref>{{cite web
 | last=Harra | first=Louise
 |author2=Milligan, Ryan |author3=Fleck, Bernhard
  | date=April 2, 2008
 | url=http://www.esa.int/esaSC/SEMJQK5QGEF_index_0.html
 | title=Hinode: source of the slow solar wind and superhot flares
 | publisher=ESA
 | access-date=2008-05-07
}}</ref><ref>{{Cite journal|last1=Antiochos|first1=S. K.|last2=Mikić|first2=Z.|last3=Titov|first3=V. S.|last4=Lionello|first4=R.|last5=Linker|first5=J. A.|date=2011-01-01|title=A Model for the Sources of the Slow Solar Wind|journal=The Astrophysical Journal|language=en|volume=731|issue=2|pages=112|doi=10.1088/0004-637X/731/2/112|issn=0004-637X|arxiv = 1102.3704 |bibcode = 2011ApJ...731..112A |s2cid=119241929}}</ref><ref>{{Cite journal|last=Fisk|first=L. A.|date=2003-04-01|title=Acceleration of the solar wind as a result of the reconnection of open magnetic flux with coronal loops|journal=Journal of Geophysical Research: Space Physics|language=en|volume=108|issue=A4|pages=1157|doi=10.1029/2002JA009284|issn=2156-2202|bibcode = 2003JGRA..108.1157F |url=https://deepblue.lib.umich.edu/bitstream/2027.42/87652/2/287_1.pdf|url-status=live|archive-url=https://web.archive.org/web/20170816114938/https://deepblue.lib.umich.edu/bitstream/handle/2027.42/87652/287_1.pdf?sequence=2|archive-date=2017-08-16|hdl=2027.42/87652|hdl-access=free}}</ref> Observations of the Sun between 1996 and 2001 showed that emission of the slow solar wind occurred at latitudes up to 30–35° during the [[solar minimum]] (the period of lowest solar activity), then expanded toward the poles as the solar cycle approached maximum. At [[solar maximum]], the poles were also emitting a slow solar wind.<ref name="McComas 1517"/>

The fast solar wind originates from [[coronal hole]]s,<ref>Zirker, J. B. (1977), Coronal holes and high‐speed wind streams, ''Reviews of Geophysics'', ''15''(3), 257–269</ref> which are funnel-like regions of open field lines in the Sun's [[magnetic field]].<ref>{{cite journal
 | last=Hassler | first=Donald M.
 |author2=Dammasch, Ingolf E. |author3=Lemaire, Philippe |author4=Brekke, Pål |author5=Curdt, Werner |author6=Mason, Helen E. |author7=Vial, Jean-Claude |author8= Wilhelm, Klaus
 | title=Solar Wind Outflow and the Chromospheric Magnetic Network
 | journal=Science | date=1999 | volume=283
 | issue=5403 | pages=810–813
 | doi=10.1126/science.283.5403.810
 | pmid=9933156 |bibcode = 1999Sci...283..810H }}</ref> Such open lines are particularly prevalent around the Sun's magnetic poles. The plasma source is small magnetic fields created by [[convection cell]]s in the solar atmosphere. These fields confine the plasma and transport it into the narrow necks of the coronal funnels, which are located only 20,000&nbsp;km above the photosphere. The plasma is released into the funnel when these magnetic field lines reconnect.<ref>{{cite journal
 | last=Marsch | first=Eckart |author2=Tu, Chuanyi
  | date=April 22, 2005
 | url=http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=36998
 | title=Solar Wind Origin in Coronal Funnels
 | journal=Science | volume=308 | issue=5721 | pages=519–23 | publisher=ESA | doi=10.1126/science.1109447 | pmid=15845846 | bibcode=2005Sci...308..519T | s2cid=24085484 | access-date=2008-05-06 }}</ref>

=== Velocity and density ===
Near the Earth's orbit at 1 [[astronomical unit]] (AU) the plasma flows at speeds ranging from 250 to 750&nbsp;km/s with a density ranging between 3 and 10 particles per cubic centimeter and temperature ranging from 10<sup>4</sup> to 10<sup>6</sup> [[kelvin]].<ref>{{Cite web |last=NOAA |date= |title=REAL TIME SOLAR WIND |url=https://www.swpc.noaa.gov/products/real-time-solar-wind |access-date=June 12, 2022}}</ref>

On average, the plasma density decreases with the square of the distance from the Sun,<ref name=:0>{{Cite journal |last1=Borgazzi |first1=A. |last2=Lara |first2=A. |last3=Echer |first3=E. |last4=Alves |first4=M. V. |date=May 2009 |title=Dynamics of coronal mass ejections in the interplanetary medium |journal=Astronomy & Astrophysics |volume=498 |issue=3 |pages=885–889 |bibcode=2009A&A...498..885B |doi=10.1051/0004-6361/200811171 |issn=0004-6361 |doi-access=free}}</ref>{{rp|at=Sect. 2.4}} while the velocity decreases and flattens out at 1&nbsp;AU.<ref name=:0 />{{rp|at=Fig. 5}}

[[Voyager 1]] and [[Voyager 2]] reported plasma density ''n'' between 0.001 and 0.005&nbsp;particles/cm<sup>3</sup> at distances of 80 to 120&nbsp;AU, increasing rapidly beyond 120&nbsp;AU at [[heliosphere|heliopause]] to between 0.05 and 0.2&nbsp;particles/cm<sup>3</sup>.<ref>{{Cite journal |last1=Gurnett |first1=D. A. |last2=Kurth |first2=W. S. |date=2019-11-04 |title=Plasma densities near and beyond the heliopause from the Voyager 1 and 2 plasma wave instruments |url=https://www.nature.com/articles/s41550-019-0918-5 |journal=Nature Astronomy |language=en |volume=3 |issue=11 |pages=1024–1028 |doi=10.1038/s41550-019-0918-5 |bibcode=2019NatAs...3.1024G |s2cid=209934074 |issn=2397-3366}}</ref>

===Pressure===
At {{val|1|ul=AU}}, the wind exerts a pressure typically in the range of {{val|1|-|6|u=nPa}} ({{val|1|-|6|e=-9|u=N/m2}}),<ref>{{cite journal
 | last=Shue | first=J. H. 
 | title=Magnetopause location under extreme solar wind conditions
 | journal=Journal of Geophysical Research
 | date=1998 | volume=103 | issue=A8 
 | pages=17,691–17,700
 | bibcode=1998JGR...10317691S 
 | doi= 10.1029/98JA01103| doi-access=free}}</ref> although it can readily vary outside that range.

The [[ram pressure]] is a [[Function (mathematics)|function]] of wind speed and density. The formula is

:<math>P = m_\text{p} \cdot n \cdot V^2 = \mathrm{1.6726 \times 10^{-27} \, kg} \cdot n \cdot V^2</math>

where ''m''<sub>p</sub> is the [[proton]] mass, pressure ''P'' is in Pa (pascals), ''n'' is the density in particles/cm<sup>3</sup> and ''V'' is the speed in km/s of the solar wind.<ref>{{Cite book | title=Plasma Physics: An Introductory Course | last = Dendy | first = Richard | publisher = Cambridge University Press | year=1995 | isbn=9780521484527 | pages=234}}</ref>

===Coronal mass ejection===
{{Main|Coronal mass ejection}}

[[File:Magnificent CME Erupts on the Sun - August 31.jpg|thumb|CME erupts from Earth's Sun]]
Both the fast and slow solar wind can be interrupted by large, fast-moving bursts of plasma called [[coronal mass ejection]]s, or CMEs. CMEs are caused by a release of magnetic energy at the Sun. CMEs are often called "solar storms" or "space storms" in the popular media. They are sometimes, but not always, associated with [[solar flare]]s, which are another manifestation of magnetic energy release at the Sun. CMEs cause shock waves in the thin plasma of the heliosphere, launching electromagnetic [[wave]]s and accelerating particles (mostly [[proton]]s and [[electrons]]) to form showers of [[ionizing radiation]] that precede the CME.<ref>{{Cite web|title=Coronal Mass Ejections {{!}} NOAA / NWS Space Weather Prediction Center|url=https://www.swpc.noaa.gov/phenomena/coronal-mass-ejections|access-date=2022-01-19|website=www.swpc.noaa.gov}}</ref>

When a CME impacts the Earth's magnetosphere, it temporarily deforms the Earth's [[magnetic field]], changing the direction of [[compass]] needles and inducing large electrical ground currents in Earth itself; this is called a [[geomagnetic storm]] and it is a global phenomenon. CME impacts can induce [[magnetic reconnection]] in Earth's [[Magnetosphere#Magnetic tails|magnetotail]] (the midnight side of the magnetosphere); this launches protons and electrons downward toward Earth's atmosphere, where they form the [[Aurora (phenomenon)|aurora]].

CMEs are not the only cause of [[space weather]]. Different patches on the Sun are known to give rise to slightly different speeds and densities of wind depending on local conditions. In isolation, each of these different wind streams would form a spiral with a slightly different angle, with fast-moving streams moving out more directly and slow-moving streams wrapping more around the Sun. Fast-moving streams tend to overtake slower streams that originate [[west]]ward of them on the Sun, forming turbulent co-rotating interaction regions that give rise to wave motions and accelerated particles, and that affect Earth's magnetosphere in the same way as, but more gently than, CMEs. 

CMEs have a complex internal structure, with a highly [[turbulent]] region of hot and compressed plasma (known as sheath) preceding an arrival of relatively cold and strongly magnetized plasma region (known as magnetic cloud or ejecta).<ref>{{cite journal |last1=Tsurutani|first1=B.T.|last2=Gonzalez|first2=W.D.|last3=Gonzalez|first3=A.L.C.|last4=Guarnieri|first4=F.L.|display-authors=et al.|title= Corotating solar wind streams and recurrent geomagnetic activity: A review | journal=Journal of Geophysical Research|date=2006-06-29|volume=111|issue=A7|doi=10.1029/2005JA011273|bibcode=2006JGRA..111.7S01T |url=http://urlib.net/sid.inpe.br/mtc-m16@80/2006/08.02.14.43 }}</ref> Sheath and ejecta have very different impact on the Earth's [[magnetosphere]] and on various [[space weather]] phenomena, such as the behavior of [[Van Allen radiation belts]].<ref>{{cite journal |last1=Pokhotelov|first1=D.|last2=Rae |first2=I.J.|last3=Murphy|first3=K.R.|last4=Mann|first4=I.R.|display-authors=et al. |title= Effects of ULF wave power on relativistic radiation belt electrons: 8-9 October 2012 geomagnetic storm | journal=Journal of Geophysical Research: Space Physics|date=2016-11-21|volume=121|issue=12|doi=10.1002/2016JA023130|bibcode=2016JGRA..12111766P }}</ref>

===Magnetic switchbacks===
[[File:Switchbacks on the Sun.gif|thumb|[[Parker Solar Probe]] observed switchbacks — traveling disturbances in the solar wind that caused the magnetic field to bend back on itself.]]
[[Magnetic switchback]]s are sudden reversals in the [[magnetic field]] of the solar wind.<ref name="New Insight">{{cite web |last1=Hatfield |first1=Miles |title=New Insight Into Parker Solar Probe's Early Observations |url=https://www.nasa.gov/feature/goddard/2020/new-insight-into-parker-solar-probes-early-observations |website=NASA |date=29 April 2020}}{{PD-notice}}</ref> They can also be described as traveling disturbances in the solar wind that caused the magnetic field to bend back on itself. They were first observed by the NASA–ESA  mission ''[[Ulysses (spacecraft)|Ulysses]]'', the first spacecraft to fly over the [[Sun]]'s poles.<ref name="nasa-Switchbacks">{{cite web |last1=Hatfield |first1=Miles |title=Switchbacks Science: Explaining Parker Solar Probe's Magnetic Puzzle |url=https://www.nasa.gov/feature/goddard/2021/switchbacks-science-explaining-parker-solar-probe-s-magnetic-puzzle |website=NASA |access-date=31 July 2022 |date=8 March 2021}}{{PD-notice}}</ref><ref name=fisk-casper>{{cite journal |last1=Fisk |first1=L. A. |last2=Kasper |first2=J. C. |title=Global Circulation of the Open Magnetic Flux of the Sun |journal=The Astrophysical Journal Letters |date=1 May 2020 |volume=894 |issue=1 |pages=L4 |doi=10.3847/2041-8213/ab8acd|bibcode=2020ApJ...894L...4F |s2cid=218640684 |doi-access=free }}[[File:CC BY icon.svg|50px]] Material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/3.0/ Creative Commons Attribution 3.0]</ref> [[Parker Solar Probe]] observed first switchbacks in 2018.<ref name="nasa-Switchbacks"/>