a) Magnetic setup at the start of the simulation showing the logarithm of the magnetic field strength in gauss. The white contour displays the equipartition level, where c_s = c_A. The crosses indicate three different locations of local wave excitation, individually discussed in Sect. 3. b) Corresponding temperature in Kelvin (colors) and velocity (arrows). The longest arrows correspond to 10 km s^-1. The dashed curve indicates optical depth τ_c = 1.