Helicity in the northern outer atmosphere. The values are written out at the point, r = 1.5 R, 90° − θ = 17°, and ϕ = 9°. Top panel: phase relation between the toroidal B_ϕ and poloidal B_θ field, plotted over time t/τ. Bottom panel: helicity H(k) is plotted over normalized wavenumber kR. The helicity is calculated with the Taylor hypothesis using the Fourier transformation of the poloidal and toroidal field. Adapted from Warnecke et al. (2011).