Ajay Kumar at 07:33, 2 September 2023

2023-09-02T07:33:32Z

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{{Short description|Magnetic field within the Solar System}}
{{More citations needed|date=December 2016}}
[[File:Heliospheric-current-sheet.gif|thumb|200px|The [[heliospheric current sheet]] is a three-dimensional form of a Parker spiral that results from the influence of the [[Sun]]'s [[rotating magnetic field]] on the [[plasma (physics)|plasma]] in the [[interplanetary medium]].<ref>http://wso.stanford.edu/gifs/helio.gif {{Bare URL image|date=March 2022}}</ref>]]

The '''interplanetary magnetic field''' ('''IMF'''), now more commonly referred to as the '''heliospheric magnetic field''' ('''HMF'''),<ref>{{cite journal |last1=Owens |first1=Mathew J. |last2=Forsyth |first2=Robert J. |date=2013-11-28 |title=The Heliospheric Magnetic Field |journal=Living Reviews in Solar Physics |language=en |volume=10 |issue=1 |pages=5 |doi=10.12942/lrsp-2013-5 |issn=2367-3648 |bibcode=2013LRSP...10....5O |arxiv=1002.2934|s2cid=122870891 }}</ref> is the component of the [[solar magnetic field]] that is dragged out from the solar [[Stellar corona|corona]] by the [[solar wind]] flow to fill the [[Solar System]].

==Coronal and solar wind plasma==
The [[solar corona|coronal]] and solar wind [[Plasma (physics)|plasma]]s are highly [[Conductor (material)|electrically conductive]], meaning the [[Magnetic field|magnetic field line]]s and the plasma flows are [[Alfvén's Theorem|effectively "frozen" together]]<ref>{{Citation|last=Roberts|first=Paul H.|chapter=Alfvén's Theorem and the Frozen Flux Approximation|date=2007|encyclopedia=Encyclopedia of Geomagnetism and Paleomagnetism|pages=7–11|editor-last=Gubbins|editor-first=David|publisher=Springer Netherlands|language=en|doi=10.1007/978-1-4020-4423-6_5|isbn=9781402044236|editor2-last=Herrero-Bervera|editor2-first=Emilio}}</ref> and the magnetic field cannot [[Diffusion|diffuse]] through the plasma on time scales of interest. In the solar corona, the magnetic pressure greatly exceeds the plasma pressure and thus [[Coronal loop|the plasma is primarily structured and confined by the magnetic field]]. However, with increasing altitude through the corona, the solar wind accelerates as it extracts energy from the magnetic field through the [[Lorentz force]] interaction, resulting in the flow momentum exceeding the restraining [[magnetic tension force]] and the coronal magnetic field is dragged out by the solar wind to form the HMF.

The dynamic [[pressure]] of the wind dominates over the [[magnetic pressure]] through most of the Solar System (or [[heliosphere]]), so that the magnetic field is pulled into an [[Archimedean spiral]] pattern (the [[Parker spiral]]<ref>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>) by the combination of the outward motion and the [[solar rotation|Sun's rotation]]. In near-Earth space, the HMF nominally makes an angle of approximately 45° to the Earth–Sun line, though this angle varies with solar wind speed. The angle of the HMF to the radial direction reduces with helio-latitude, as the speed of the photospheric footpoint is reduced.

Depending on the polarity of the photospheric footpoint, the heliospheric magnetic field spirals inward or outward; the magnetic field follows the same shape of spiral in the northern and southern parts of the heliosphere, but with opposite field direction. These two magnetic domains are separated by a two [[current sheet]] (an [[electric current]] that is confined to a curved plane). This [[heliospheric current sheet]] has a shape similar to a twirled [[ballerina]] skirt, and changes in shape through the solar cycle as the Sun's magnetic field reverses about every 11 years.

==Magnetic field at Earth orbit==
[[File:Animati3.gif|thumb|155px|A video simulation of Earth's magnetic field interacting with the (solar) interplanetary magnetic field (IMF)]]
The [[Plasma (physics)|plasma]] in the [[interplanetary medium]] is also responsible for the strength of the Sun's magnetic field at the orbit of the Earth being over 100 times greater than originally anticipated. If space were a vacuum, then the Sun's magnetic dipole field — about 10−4 [[Tesla (unit)|teslas]] at the surface of the Sun — would reduce with the inverse cube of the distance to about 10−11 teslas. But satellite observations show that it is about 100 times greater at around 10−9 teslas. [[Magnetohydrodynamic]] (MHD) theory predicts that the motion of a conducting fluid (e.g., the interplanetary medium) in a magnetic field induces electric currents, which in turn generates magnetic fields — and, in this respect, it behaves like an [[MHD dynamo]].

The interplanetary magnetic field at the Earth's orbit varies with waves and other disturbances in the solar wind, known as "[[space weather]]." The field is a vector, with components in the radial and azimuthal directions as well as a component perpendicular to the ecliptic. The field varies in strength near the Earth from 1 to 37 nT, averaging about 6 nT.<ref>Glossary, [http://pluto.space.swri.edu/image/glossary/IMF.html interplanetary magnetic field (IMF)] {{Webarchive|url=https://web.archive.org/web/20120429193636/http://pluto.space.swri.edu/image/glossary/IMF.html |date=2012-04-29 }}, Southwest Research Institute. Retrieved 11 February 2020.</ref> Since 1997, the solar magnetic field has been monitored in real time by the [[Advanced Composition Explorer]] (ACE) satellite located in a halo orbit at the Sun–Earth [[Lagrangian point|Lagrange Point]] L1; since July 2016, it has been monitored by the [[Deep Space Climate Observatory]] (DSCOVR) satellite, and also at Sun–Earth L1 (with the ACE continuing to serve as a back-up measurement).<ref>[https://www.spaceweatherlive.com/en/help/the-interplanetary-magnetic-field-imf The Interplanetary Magnetic Field (IMF)], Space Weather Live. Retrieved 11 February 2020.</ref>

==See also==
*[[Solar magnetic field]]
*[[Solar wind]]
*[[Magnetosphere]]
*[[List of plasma (physics) articles]]

==References==
{{Commons category|Interplanetary magnetic field}}
{{reflist}}

{{Magnetosphere}}

[[Category:Solar System]]
[[Category:Outer space]]
[[Category:Magnetism in astronomy]]

Interplanetary magnetic field - Revision history

Ajay Kumar at 07:33, 2 September 2023