Evolution of Magnetic Helicity and Energy Spectra of Solar Active Regions

Hongqi Zhang, Axel Brandenburg, D. D. Sokoloff

Published 2015-03-03Version 1

We adopt an isotropic representation of the Fourier-transformed two-point correlation tensor of the magnetic field for estimating magnetic energy and helicity spectra as well as current helicity spectra of individual active regions and the change of their spectral indices with the solar cycle. The departure of the spectral index of current helicity from 5/3 is analyzed, and it is found that it is lower than that of magnetic energy. There is no obvious relationship between the change of the normalized magnetic helicity and the integral scale of the magnetic field for individual active regions. The evolution of the spectral index reflects the development and distribution of various scales of magnetic structures in active regions. It is found that around solar maximum the magnetic energy and helicity spectra are steeper.