Fig. 4: Results of 3D MHD simulations of wave propagation along an overdense open coronal waveguide.

a, Forward modelled 1,074-nm emission from a flux tube supporting both propagating kink and torsional Alfvén waves. The emission is shown from an LOS that is 45° to the plane of motion of the kink mode. b, Corresponding Doppler velocity, which shows a pattern dominated by the kink motions. c, Residual Doppler velocity, estimated in the same manner as the observations. Within the flux tube, the pattern of an n = 0 torsional Alfvén mode is clearly visible. d, Doppler velocities of an individual kink (pink dashed line) and torsional modes (lower edge in purple and upper edge in green). In this simulation of a single flux tube, the amplitudes are larger than the corresponding observed values, which are thought to result from averaging wave motions from several flux tubes along the LOS. The blue dashed lines in a–c indicate the measured centre of the flux tube.