Heliospheric current sheet: Difference between revisions

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{{Short description|Surface of magnetic polarity change}}

[[ImageFile:Heliospheric-current-sheet_editsheet.jpggif|thumb|300px|Heliospheric current sheet]]

The '''heliospheric current sheet''', or '''interplanetary current sheet''', is a surface separating regions of the [[heliosphere]] where the [[interplanetary magnetic field]] points toward and away from the [[Sun]].<ref>{{Citation | title = The heliospheric current sheet | year = 2001 | last1 = Smith | first1 = Edward J. | journal = [[Journal of Geophysical Research]] | volume = 106 | pages = 15819 | doi = 10.1029/2000JA000120 | bibcode = 2001JGR...10615819S}}</ref> A small [[electrical current]] with a [[current density]] of about 10⁻¹⁰ [[ampere|A]]/m² flows within this surface, forming a [[current sheet]] confined to this surface.<ref name="israelevich2001">Israelevich, P. L., ''et al.'', "[http://aanda.u-strasbg.fr/articles/aa/abs/2001/34/aah2814/aah2814.html MHD simulation of the three-dimensional structure of the heliospheric current sheet] {{Webarchive|url=https://web.archive.org/web/20170323235736/http://aanda.u-strasbg.fr/articles/aa/abs/2001/34/aah2814/aah2814.html |date=2017-03-23 }}" (2001) ''Astronomy and Astrophysics'', v.376, p.288–291</ref><ref>[https://science.nasa.gov/headlines/y2003/22apr_currentsheet.htm A Star with two North Poles] {{webarchive|url=https://web.archive.org/web/20090718014855/https://science.nasa.gov/headlines/y2003/22apr_currentsheet.htm |date=2009-07-18 }}, April 22, 2003, Science @ NASA</ref><ref>Riley, Pete; Linker, J. A.; Mikić, Z., "[https://ui.adsabs.harvard.edu/abs/2002JGRA.107g.SSH8R Modeling the heliospheric current sheet: Solar cycle variations]", (2002) ''Journal of Geophysical Research'' (Space Physics), Volume 107, Issue A7, pp. SSH 8-1, CiteID 1136, DOI 10.1029/2001JA000299. ([http://ulysses.jpl.nasa.gov/science/monthly_highlights/2002-July-2001JA000299.pdf Full text] {{webarchive|url=https://web.archive.org/web/20090814052347/http://ulysses.jpl.nasa.gov/science/monthly_highlights/2002-July-2001JA000299.pdf |date=2009-08-14 }})</ref> The shape of the current sheet results from the influence of the Sun's [[rotating magnetic field]] on the [[Plasma (physics)|plasma]] in the [[interplanetary medium]].<ref>{{cite web|url=http://quake.stanford.edu/~wso/gifs/HCS.html |title=Artist's Conception of the Heliospheric Current Sheet |access-date=2005-11-20 |url-status=bot: unknown |archive-url=https://web.archive.org/web/20060901124602/http://quake.stanford.edu/~wso/gifs/HCS.html |archive-date=September 1, 2006 }}</ref> The thickness of the current sheet is about {{cvt|10,000|km|mi}} near the orbit of the Earth.

The '''Heliospheric current sheet''' (HCS), is the largest structure in the [[Solar System]] [http://science.nasa.gov/headlines/y2003/22apr_currentsheet.htm], resulting from the influence of the Sun's rotating magnetic field on the [[plasma]] in the [[interplanetary medium]] ([[Solar Wind]]) [http://quake.stanford.edu/~wso/gifs/HCS.html]. The [[current sheet]] occurs in Sun's equatorial plane where the Sun's magnetic field changes polarity from plus (north) to minus (south). The thickness of the current sheet is about 10,000km.

The underlying magnetic field is called the '''interplanetary magnetic field''', and the resuling electric current forms part of the '''heliospheric current circuit'''.{{ref|Israelevich2001}}

==Characteristics==

===Ballerina's skirt Shape===

===Ballerina's skirt Shapeshape===

As the Sun rotates, its magnetic fields twist into an [[Archimedean spiral]] (or [[Parker spiral]] {{ref|parker1958}}, named after its discovery by [[Eugene Parker]]). As the spiraling magnetic sheets changes polarity, it warps into a wavy spiral shape has been likened to a ballerina's skirt {{ref|wilcox1980}}. Further dynamics have suggested that "The Sun with the heliosheet is like a bashful ballerina who is repeatedly trying to push her excessively high flaring skirt downward". {{ref|Mursula2003}}

[[File:Parker spiral.gif|thumb|right|300px|The Parker Spiral]]

As the Sun rotates, its magnetic field twists into an [[Archimedean spiral]], as it extends through the Solar System. This phenomenon is often called the '''Parker spiral''', after [[Eugene Parker]]'s work<ref name="parker1958">{{Citation | title = Dynamics of the Interplanetary Gas and Magnetic Fields. | year = 1958 | last1 = Parker | first1 = E. N. | journal = [[The Astrophysical Journal]] | volume = 128 | pages = 664 | doi = 10.1086/146579 | bibcode = 1958ApJ...128..664P}}</ref> that predicted the structure of the interplanetary magnetic field.

=== Magnetic field ===

The spiral nature of the heliospheric magnetic field was noted earlier by [[Hannes Alfvén]],<ref>{{Citation | title = On the theory of comet tails. | year = 1957 | last1 = Alfven | first1 = H. | journal = [[Tellus]] | volume = 9 | pages = 92 | doi = 10.3402/tellusa.v9i1.9064 | bibcode = 1957Tell....9...92A| doi-access = free }}</ref> based on the structure of comet tails.

The influence of this spiral-shaped magnetic field on the [[interplanetary medium]] ([[solar wind]]) creates the largest structure in the Solar System, the heliospheric current sheet. Parker's spiral magnetic field was divided in two by a [[current sheet]],<ref>{{Citation | title = Current sheet magnetic model for the solar corona. | year = 1971 | last1 = Schatten | first1 = K. H. | journal = Cosmic Electrodynamics | volume = 2 | pages = 232 | bibcode = 1971CosEl...2..232S}}</ref> a mathematical model first developed in the early 1970s by Schatten. It warps into a wavy spiral shape that has been likened to a [[ballerina skirt]].<ref name="rosenberg1969">{{Citation | title = Heliographic latitude dependence of the dominant polarity of the interplanetary magnetic field | year = 1969 | last1 = Rosenberg | first1 = Ronald L. | last2 = Coleman | first2 = Paul J. Jr. | journal = [[Journal of Geophysical Research]] | volume = 74 | pages = 5611 | doi = 10.1029/JA074i024p05611 | bibcode = 1969JGR....74.5611R}}</ref><ref name="wilcox1980">{{Citation | title = The origin of the warped heliospheric current sheet | year = 1980 | last1 = Wilcox | first1 = J. M. | last2 = Scherrer | first2 = P. H. | last3 = Hoeksema | first3 = J. T. | journal = NASA STI/Recon Technical Report N | volume = 81 | pages = 33113 | doi = | bibcode = 1980STIN...8133113W}}</ref> The waviness of the current sheet is due to the magnetic field dipole axis' tilt angle to the solar rotation axis and variations from an ideal dipole field.<ref>{{cite journal|last1=Owens|first1=M. J.|last2=Forsyth|first2=R. J.|title=The Heliospheric Magnetic Field|journal=Living Reviews in Solar Physics|date=2013|volume=10|issue=1|page=11|doi=10.12942/lrsp-2013-5|doi-access=free |bibcode = 2013LRSP...10....5O |arxiv=1002.2934|s2cid=122870891}}</ref>

The heliospheric current sheet rotates along with the Sun once every 27 days, during which time the peaks and troughs of the skirt pass through the Earth's magnetosphere, interacting with it. Near the surface of the Sun, the magnetic field produced by the radial electric current (see below) in the sheet is of the order of 5x10^-6T.{{ref|Israelevich2001}}

Unlike the familiar shape of the field from a bar [[magnet]], the Sun's extended field is twisted into an [[arithmetic spiral]] by the [[magnetohydrodynamic]] influence of the [[solar wind]]. The [[solar wind]] travels outward from the Sun at a rate of 200–800 km/s, but an individual jet of solar wind from a particular feature on the Sun's surface rotates with the [[solar rotation]], making a spiral pattern in space. The cause of this ballerina spiral shape has sometimes been called the "garden sprinkler effect" or "garden hose effect",<ref name="Louise K. Harra 2004">Louise K. Harra, Keith O. Mason, ''Space Science'' 2004, Imperial College Press, {{ISBN|1-86094-361-6}}</ref><ref name="trs-new.jpl.nasa.gov">Smith, E., "[http://trs-new.jpl.nasa.gov/dspace/handle/2014/18860?mode=simple The Sun, Solar Wind, and Magnetic Field] {{webarchive|url=https://web.archive.org/web/20080205054035/http://trs-new.jpl.nasa.gov/dspace/handle/2014/18860?mode=simple |date=2008-02-05 }}", Jul 1999, Proceedings of the International School of Physics Enrico FERMI Varenna, Italy</ref> because it is likened to a [[irrigation sprinkler|lawn sprinkler]] with nozzle that moves up and down while it spins; the stream of water represents the solar wind. Unlike the jet from a sprinkler, however, the solar wind is tied to the [[magnetic field]] by [[magnetohydrodynamics|MHD]] effects, so that magnetic field lines are tied to the material in the jet and take on an arithmetic spiral shape.

The magnetic field at the surface of the Sun is about 10^-4 tesla. If the form of the field were a [[magnetic dipole]], the strength would decrease with the cube of the distance, resulting in about 10^-11 tesla at the Earth's orbit. The heliospheric current sheet results in higher order multipole components so that the actual magnetic field at the Earth due to the Sun is 100 times greater.

The Parker spiral shape of the solar wind changes the shape of the Sun's magnetic field in the [[outer Solar System]]: beyond about 10–20 [[astronomical units]] from the Sun, the magnetic field is nearly [[toroid (geometry)|toroid]]al (pointed around the equator of the Sun) rather than [[poloidal]] (pointed from the North to the South pole, as in a bar magnet) or [[wikt:radial|radial]] (pointed outward or inward, as might be expected from the flow of the solar wind if the Sun were not rotating). The spiral shape also greatly amplifies the strength of the solar magnetic field in the outer Solar System.

===Electric Current===

The Parker spiral may be responsible for the differential [[solar rotation]], in which the Sun's poles rotate more slowly (about a 35-day rotation period) than the equator (about a 27-day rotation period). The solar wind is guided by the Sun's magnetic field and hence largely emanates from the polar regions of the Sun; the induced spiral shape of the field causes a drag torque on the poles due to the [[magnetic tension force]].

The electric current in the heliospheric current sheet is directed radially inward, the circuit being closed by outward currents aligned with the Sun's magnetic field in the solar polar regions. The total current in the circuit is on the order of 3&times;10⁹ [[ampere]]s{{ref|Israelevich2001}}. As a comparison with other astrophysical electric currents, the [[Birkeland current]]s that supply the Earth's [[aurora]] are about a thousand times weaker at a million amperes. The maximum current density in the sheet is on the order of 10^-10 A/m² (10^-4 amps/km²).

During [[solar maximum]] the entire magnetic field of the Sun flips, thus alternating the polarity of the field every [[solar cycle]].<ref name="nasaSolarmag">{{cite web|url=http://helios.gsfc.nasa.gov/solarmag.html|archive-url=https://web.archive.org/web/19981202055322/http://helios.gsfc.nasa.gov/solarmag.html|url-status=dead|archive-date=1998-12-02|title=NASA's Cosmicopia – Sun – Sun's Magnetic Field|first=Beth|last=Barbier}}</ref>

==History==

=== Magnetic field ===

The Heliospheric current sheet was discovered by John M. Wilcox and Norman F. Ness, who published their finding in a 1965 {{ref|wilcox1965}}. Hannes Alfvén and Per Carlqvist speculate {{ref|alfven1978}} on the existence of a galactic current sheet, a counterpart of the heliospheric current sheet, with an estimated galactic current of 10¹⁷ - 10¹⁹ Amps, that might flow in the plane of symmetry of the galaxy.

{{Heliophysics}}

The heliospheric current sheet rotates along with the Sun oncewith a period of everyabout 2725 days, during which time the peaks and troughs of the skirt pass through the Earth's magnetosphere, interacting with it. Near the surface of the Sun, the magnetic field produced by the radial electric current (see below) in the sheet is of the order of 5x10^-6T.{{refval|Israelevich20015|e=-6|u=T}}.<ref name="israelevich2001" />

The magnetic field at the surface of the Sun is about 10^{{val|e=-4 tesla|ul=T}}. If the form of the field were a [[magnetic dipole]], the strength would decrease with the cube of the distance, resulting in about 10^{{val|e=-11 tesla|ul=T}} at the Earth's orbit. The heliospheric current sheet results in higher order multipole components so that the actual magnetic field at the Earth due to the Sun is 100 times greater.

==External Links==

===Electric Currentcurrent===

*[http://www.izmiran.rssi.ru/magnetism/SSIMF/SB/mfi/hcs.html The Heliospheric Current Sheet]

*[http://www.firstscience.com/site/articles/north.asp A Star With Two North Poles] (features animation)

*[http://pluto.space.swri.edu/IMAGE/glossary/IMF.html The interplanetary magnetic field]

*[http://gse.gi.alaska.edu/recent/3DHCS.html 3-Dimensional View of the Heliospheric Current Sheet]

*[http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&sim_query=YES&aut_xct=NO&aut_logic=OR&obj_logic=OR&author=&object=&start_mon=&start_year=&end_mon=&end_year=&ttl_logic=OR&title=%22Heliospheric+Current+Sheet%22&txt_logic=OR&text=&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&obj_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1 NASA Astrophysics Data System article references] ([http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&sim_query=YES&aut_xct=NO&aut_logic=OR&obj_logic=OR&author=&object=&start_mon=&start_year=&end_mon=&end_year=&ttl_logic=OR&title=%22Heliospheric+Current+Sheet%22&txt_logic=OR&text=&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=YES&gif_link=YES&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&obj_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1 Online full text articles])

The electric current in the heliospheric current sheet ishas directeda radiallyradial component (directed inward) as well as an [[azimuthal]] component, the radial circuit being closed by outward currents aligned with the Sun's magnetic field in the solar polar regions. The totalradial current in the circuit is on the order of {{val|3&times;10^|e=9 |u=[[ampere]]s{{ref|Israelevich2001}}.<ref name="israelevich2001" /> As a comparison with other astrophysical electric currents, the [[Birkeland current]]s that supply the Earth's [[Aurora (astronomy)|aurora]] are about a thousand times weaker at a million amperes. The maximum current density in the sheet is on the order of 10^{{val|e=-10 |u=A/m²}} (10^{{val|e=-4 amps|u=A/km²}}).

==History==

The heliospheric current sheet was discovered by [[John M. Wilcox]] and [[Norman F. Ness]], who published their finding in 1965.<ref name="wilcox1965">{{cite journal |first1=John M. |last1=Wilcox |first2=Norman F. |last2=Ness |title=Quasi-Stationary Corotating Structure in the Interplanetary Medium |date=1965 |journal=[[Journal of Geophysical Research]] |volume=70 |issue=23 |pages=5793–5805 |doi=10.1029/JZ070i023p05793 |bibcode = 1965JGR....70.5793W |hdl=2060/19660001924 |s2cid=121122792 |hdl-access=free }}</ref> [[Hannes Alfvén]] and [[Per Carlqvist]] speculate on the existence of a [[galactic current sheet]], a counterpart of the heliospheric current sheet, with an estimated galactic current of 10¹⁷ to 10¹⁹ amperes, that might flow in the plane of symmetry of the galaxy.<ref name="alfven1978">{{cite journal |first1=Hannes |last1=Alfvén |first2=Per |last2=Carlqvist |bibcode=1978Ap&SS..55..487A |title=Interstellar clouds and the formation of stars |date=1978 |journal=Astrophysics and Space Science |volume=55 |issue=2 |pages=487–509 |doi= 10.1007/bf00642272|s2cid=122687137 |url=https://cds.cern.ch/record/118596 }}</ref>

==References==

{{reflist|2}}

==External Linkslinks==

*[https://web.archive.org/web/20060721120205/http://www.izmiran.rssi.ru/magnetism/SSIMF/SB/mfi/hcs.html The Heliospheric Current Sheet]

*[http://www.firstscience.com/site/articles/north.asp A Star With Two North Poles] (features animation)

*[http://pluto.space.swri.edu/IMAGE/glossary/IMF.html The interplanetary magnetic field] {{Webarchive|url=https://web.archive.org/web/20120429193636/http://pluto.space.swri.edu/image/glossary/IMF.html |date=2012-04-29 }}

*[https://web.archive.org/web/20111113225043/http://gse.gi.alaska.edu/recent/3DHCS.html 3-Dimensional View of the Heliospheric Current Sheet]

*[http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&sim_query=YES&aut_xct=NO&aut_logic=OR&obj_logic=OR&author=&object=&start_mon=&start_year=&end_mon=&end_year=&ttl_logic=OR&title=%22Heliospheric+Current+Sheet%22&txt_logic=OR&text=&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&obj_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1 NASA Astrophysics Data System article references] ([http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&sim_query=YES&aut_xct=NO&aut_logic=OR&obj_logic=OR&author=&object=&start_mon=&start_year=&end_mon=&end_year=&ttl_logic=OR&title=%22Heliospheric+Current+Sheet%22&txt_logic=OR&text=&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=&data_and=YES&gif_link=YES&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&obj_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1 Online full text articles])

{{Magnetospherics}}

*{{ref|alfven1978}}Hannes Alfvén and Per Carlqvist, "[http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1978Ap%26SS..55..487A Interstellar clouds and the formation of stars]" (1978) in ''Astrophysics and Space Science'', vol. 55, no. 2, May 1978, p. 487-509.

{{The Sun}}

*{{note|wilcox1965}}John M. Wilcox and Norman F. Ness, "Quasi-Stationary Corotating Structure in the Interplanetary Medium" (1965) ''Journal of Geophysical Research'', 70, 5793.

*{{note|Israelevich2001}}Israelevich, P. L., ''et al'', "[http://aanda.u-strasbg.fr:2002/papers/aa/full/2001/34/aah2814/aah2814.html MHD simulation of the three-dimensional structure of the heliospheric current sheet]" (2001) ''Astronomy and Astrophysics'', v.376, p.288-291

*{{note|Mursula2003}}Mursula, K.; Hiltula, T., "[http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003GeoRL..30vSSC2M&amp;db_key=AST&amp;data_type=HTML&amp;format=&amp;high=42ca922c9c03266 Bashful ballerina: Southward shifted heliospheric current sheet]]" (2003), Geophysical Research Letters, Volume 30, Issue 22, pp. SSC 2-1

*{{note|parker1958}}Parker, E. N., "[http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?1958ApJ...128..664P Dynamics of the Interplanetary Gas and Magnetic Fields]", (1958) ''Astrophysical Journal'', vol. 128, p.664

*{{note|wilcox1980}}Wilcox, J. M.; Scherrer, P. H.; Hoeksema, J. T., "[http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1980STIN...8133113W&amp;db_key=AST&amp;data_type=HTML&amp;format=&amp;high=42ca922c9c12139 The origin of the warped heliospheric current sheet]" (1980)

[[Category:AstronomyDynamics of the Solar System]]

[[Category:AstrophysicsSolar phenomena]]

[[Category:Plasma physicsSpirals]]

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[[Category:Space plasmas]]

[[Category:Magnetism]]