- Heliospheric current sheet
The heliospheric current sheet (HCS) is the surface within the
Solar System where the polarity of theSun 'smagnetic field changes from north to south. This field extends throughout the Sun'sequatorial plane in theheliosphere . [ [http://science.nasa.gov/headlines/y2003/22apr_currentsheet.htm A Star with two North Poles] , April 22, 2003, Science @ NASA] [Riley, Pete; Linker, J. A.; Mikić, Z., " [http://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] )] The shape of thecurrent sheet results from the influence of the Sun'srotating magnetic field on the plasma in theinterplanetary medium (Solar Wind ). [ [http://quake.stanford.edu/~wso/gifs/HCS.html] Dead link|date=March 2008] A smallelectrical current flows within the sheet, about 10−10 A/m². The thickness of the current sheet is about 10,000 km.The underlying magnetic field is called the
interplanetary magnetic field , and the resulting electric current forms part of the heliospheric current circuit.Israelevich, P. L., "et al", " [http://aanda.u-strasbg.fr/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] The Heliospheric current sheet is also sometimes called the "Interplanetary Current Sheet".Characteristics
Ballerina's skirt shape
As the Sun rotates, its magnetic field twists into a
Parker spiral ,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] a form of anArchimedean spiral , named after its discovery byEugene Parker . Parker's spiral magnetic field was divided in two by a current sheet [ " [http://www.nature.com/nature/journal/v264/n5588/abs/264730a0.html;jsessionid=55DC5F768647B390C384E7AF83122081 Current Sheet Magnetic Model for the Solar Corona] ", K. H. Schatten, Cosmic Electrodynamics, 2, 232-245, 1971.] , a mathematical model first developed in the early '70's by Schatten. As the spiraling magnetic sheet changes polarity, it warps into a wavy spiral shape that has been likened to a ballerina's skirt.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.] Wilcox, J. M.; Scherrer, P. H.; Hoeksema, J. T., " [http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1980STIN...8133113W&db_key=AST&data_type=HTML&format=&high=42ca922c9c12139 The origin of the warped heliospheric current sheet] " (1980)] 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".Mursula, K.; Hiltula, T., " [http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003GeoRL..30vSSC2M&db_key=AST&data_type=HTML&format=&high=42ca922c9c03266 Bashful ballerina: Southward shifted heliospheric current sheet] " (2003), Geophysical Research Letters, Volume 30, Issue 22, pp. SSC 2-1]The cause of the ballerina spiral shape has sometimes been called the "garden sprinkler effect" or "garden hose effect" [Louise K. Harra, Keith O. Mason, "Space Science" 2004, Imperial College Press, ISBN 1860943616] [Smith, E., " [http://trs-new.jpl.nasa.gov/dspace/handle/2014/18860?mode=simple The Sun, Solar Wind, and Magnetic Field] ", Jul 1999, Proceedings of the International School of Physics Enrico FERMI Varenna, Italy] , and likening to holding a lawn sprinkler, and moving it in your hand vertically up and down, while your body rotates. The stream of water represents the Solar Wind, and moves radially outwards at all times.
Magnetic field
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 5×10−6 T.
The magnetic field at the surface of the Sun is about 10-4
tesla . If the form of the field were amagnetic 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.Electric current
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 3×109
ampere s. As a comparison with other astrophysical electric currents, theBirkeland 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 A/km²).History
The heliospheric current sheet was discovered by John M. Wilcox and Norman F. Ness, who published their finding in a 1965.John M. Wilcox and Norman F. Ness, "Quasi-Stationary Corotating Structure in the Interplanetary Medium" (1965) "Journal of Geophysical Research", 70, 5793.] 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.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.]
References
ee also
*
Interplanetary Magnetic Field External links
* [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] )
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