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Tuesday 26 Nov 2019Spatial Scales and Locality of Magnetic Helicity

Gareth Hawkes - University of Exeter

Harrison 170 13:30-15:30

Magnetic helicity, a measure of the entanglement of a magnetic field embedded within a plasma, is approximately conserved in resistive MHD models. The transport and removal of helicity is crucial in both the dynamo in the solar interior and active region evolution in the solar corona, for which we observe highly inhomogeneous distributions of entanglement.  However, spectral helicity decompositions, which are the current dominant method for scale analysis, do not respect this inhomogeneity. We apply a multiresolution wavelet decomposition to the magnetic field and demonstrate how it can be applied to various quantities associated with magnetic helicity, including the field line helicity. We use a geometrical definition of helicity which allows these quantities to be calculated for fields with arbitrary boundary conditions. It is shown that the multiresolution decomposition of helicity has the crucial property of local additivity, and we demonstrate a general linear energy-topology conservation law.

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