- Interplanetary Magnetic Field
The Interplanetary Magnetic Field (IMF) is the term for the
Sun’s magnetic fieldcarried by the solar windamong the planets of the Solar System.
heliospheric current sheetis a three-dimensional form of a Parker spiral that results from the influence of the Sun's rotating magnetic fieldon the plasma in the interplanetary medium. [http://wso.stanford.edu/gifs/helio.gif] ] Since the solar wind is a plasma, it has the characteristics of a plasma, rather than a simple gas. For example, it is highly electrically conductive so that magnetic field lines from the Sun are carried along with the wind. The dynamic pressureof the wind dominates over the magnetic pressurethrough most of the solar system (or heliosphere), so that the magnetic field is pulled into an Archimedean spiralpattern (the Parker spiral) by the combination of the outward motion and the Sun's rotation. Depending on the hemisphere and phase of the solar cycle, the 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 currentthat is confined to a curved plane). This heliospheric current sheethas a similar shape to a twirled ballerinaskirt, and changes in shape through the solar cycle as the Sun's magnetic field reverses about every 11 years.
The plasma in the
interplanetary mediumis 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 10-4 tesla magnetic dipole field would reduce with the cube of the distance to about 10-11 tesla. But satellite observations show that it is about 100 times greater at around 10-9 tesla. 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 a MHD dynamo.
* [http://www.spaceweather.com/glossary/imf.html spaceweather.com]
* [http://pluto.space.swri.edu/image/glossary/IMF.html Southwest Research Institute]
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