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Comparing Values of the Relative Magnetic Helicity in Finite Volumes View all abstracts by submitter

Gherardo Valori   Submitted: 2012-02-13 08:59

Relative magnetic helicity, as a conserved quantity of idealmagnetohydrodynamics,has been highlighted as an important quantity to study inplasma physics. Due to its non-local nature, its estimation is notstraightforwardin both observational and numerical data. In the present study wederive expressionsfor the practical computation of the gauge-independent relative magnetichelicity in three-dimensional finite domains. The derived expressionsare easyto implement and rapid to compute. They are derived in Cartesiancoordinates,but can be easily written in other coordinate systems. We apply ourmethod to anumerical model of a force-free equilibrium containing a flux rope,and comparethe results with those obtained employing known half-space equations.We findthat our method requires a much smaller volume than half-spaceexpressionsto derive the full helicity content. Additionally, we prove thatvalues of relativemagnetic helicity of different magnetic fields can be compared witheach otherin the same sense as free-energy values can. Therefore, relativemagnetic helicitycan be meaningfully and directly compared between different datasets,such asthose from different active regions, but also the same dataset atdifferent times.Typical applications of our formulae include the helicity computationin threedimensionalmodels of the solar atmosphere, e.g. coronal-field reconstructions byforce-free extrapolation and discretized magnetic fields of numericalsimulations.

Authors: Valori, G., Demoulin, P., Pariat E.

Publication Status: Solar Phys (accepted)
Last Modified: 2012-02-17 05:38
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