Computation of Relative Magnetic Helicity in Spherical Coordinates 

Kostas Moraitis Submitted: 20180610 22:14
Magnetic helicity is a quantity of great importance in solar studies because it is conserved in ideal magnetohydrodynamics. While many methods to compute magnetic helicity in Cartesian finite volumes exist, in spherical coordinates, the natural coordinate system for solar applications, helicity is only treated approximately. We present here a method to properly compute relative magnetic helicity in spherical geometry. The volumes considered are finite, of shell or wedge shape, and the threedimensional magnetic field is considered fully known throughout the studied domain. Testing of the method with wellknown, semianalytic, forcefree magneticfield models reveals that it has excellent accuracy. Further application to a set of nonlinear forcefree reconstructions of the magnetic field of solar active regions, and comparison with an approximate method used in the past, indicates that the proposed methodology can be significantly more accurate, thus making our method a promising tool in helicity studies that employ the spherical geometry. Additionally, the range of applicability of the approximate method is determined and discussed.
Authors: Moraitis, K., Pariat, E., Savcheva, A., Valori, G.
Projects: None

Publication Status: accepted by Solar Physics
Last Modified: 20180613 12:39


