Mon 15 Oct 2018

Difference between revisions of "Heliospheric current sheet"

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[[Image:Heliospheric-current-sheet_edit.jpg|thumb|300px|Heliospheric current sheet]]
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This is the biggest structure in the solar system. Everything else is smaller. Ian knows this because he went there yesterday and measured it with a ruler.
 
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The '''Heliospheric current sheet''' (HCS) is the surface within the [[Solar System]] where the [[magnet|polarity]] of the [[Sun]]'s [[magnetic field]] changes from north to south. This field extends from the Sun's [[equatorial plane]] throughout the entire [[Solar System]] out to the [[heliosphere]].<ref>http://science.nasa.gov/headlines/y2003/22apr_currentsheet.htm</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]] ([[Solar Wind]]).<ref>http://quake.stanford.edu/~wso/gifs/HCS.html</ref> A small [[electrical current]] flows within the sheet, about 10<sup>-10 </sup> amps/m<sup>2</sup>. The thickness of the current sheet is about 10,000km.
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The underlying magnetic field is called the '''[[interplanetary magnetic field]]''', and the resulting electric current forms part of the '''[[heliospheric current circuit]]'''.<ref name="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</ref> The Heliospheric current sheet is also sometimes called the ''Interplanetary Current Sheet''.
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==Characteristics==
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===Ballerina's skirt shape===
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As the Sun rotates, its magnetic field twists into a [[Parker spiral]],<ref name="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</ref> a form of an [[Archimedean spiral]], named after its discovery by [[Eugene Parker]]. As the spiraling magnetic sheets changes polarity, it warps into a wavy spiral shape that has been likened to a ballerina's skirt.<ref name="rosenberg1969">Rosenberg, R. L. and P. J. Coleman, Jr., Heliographic latitude dependence of the dominant polarity of the interplanetary magnetic field, ''J. Geophys. Res.'', 74 (24), 5611-5622, 1969.</ref><ref name="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)</ref> 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 name="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</ref>
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=== Magnetic field ===
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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 in the sheet is of the order of 5x10<sup>-6</sup>T.<ref name="israelevich2001" />
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The magnetic field at the surface of the Sun is about 10<sup>-4</sup> 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<sup>-11</sup> 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.
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===Electric current===
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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;10<sup>9</sup> [[ampere]]s.<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<sup>-10</sup> A/m<sup>2</sup> (10<sup>-4</sup> amps/km<sup>2</sup>).
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==History==
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The heliospheric current sheet was discovered by John M. Wilcox and Norman F. Ness, who published their finding in a 1965 <ref name="wilcox1965">John M. Wilcox and Norman F. Ness, "Quasi-Stationary Corotating Structure in the Interplanetary Medium" (1965) ''Journal of Geophysical Research'', 70, 5793.</ref>. Hannes Alfvén and Per Carlqvist speculate<ref name="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.</ref> on the existence of a galactic current sheet, a counterpart of the heliospheric current sheet, with an estimated galactic current of 10<sup>17</sup> - 10<sup>19</sup> Amps, that might flow in the plane of symmetry of the galaxy.
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==References==
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<div class="references-small"><references /></div>
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==External links==
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*[http://www.izmiran.rssi.ru/magnetism/SSIMF/SB/mfi/hcs.html The Heliospheric Current Sheet]
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*[http://www.firstscience.com/site/articles/north.asp A Star With Two North Poles] (features animation)
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*[http://pluto.space.swri.edu/IMAGE/glossary/IMF.html The interplanetary magnetic field]
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*[http://gse.gi.alaska.edu/recent/3DHCS.html 3-Dimensional View of the Heliospheric Current Sheet]
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*[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])
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Revision as of 14:32, 25 February 2007

This is the biggest structure in the solar system. Everything else is smaller. Ian knows this because he went there yesterday and measured it with a ruler.