this page is about helicity in magnetic fields. For fluid mechanical helicity, see helicity
In electromagnetism, magnetic helicity is the extent to which a magnetic field "wraps around itself". If magnetic field lines follow the strands of a twisted rope, this configuration would have nonzero magnetic helicity; left handed ropes would have negative values and right handed ropes would have positive values.
The magnetichelicity is a fundamental quantity in magnetohydrodynamics because it is conserved in the limit of infinite electrical conductivity.
The reason for the anomalous scalings of the magnetichelicity correlation function is that the magnetic field in the equation for the two-point correlation function of the magnetichelicity plays a role of a pumping with anomalous scalings.
Magnetic fields exhibit dipolar, quadrupolar or hemispherical structures as long as convection in the polar regions of the spherical fluid shells is inhibited owing to a sufficiently high rate of rotation.
This paper reviews several aspects of magnetichelicity, including its history from Gauss to the present, its relation to field structure, its role in Taylor relaxation, and how it is defined for sub-volumes of space.
Magnetichelicity is conserved in ideal MHD and approximately conserved during reconnection.
In recent years, solar observers have discovered a striking pattern in the distribution of coronal magnetic structures: northern hemisphere structures tend to have negative magnetichelicity, while structures in the south tend to have positive magnetichelicity.
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