Evolution of the tube wave amplitude with distance along the plume for different values of the wave period. The dotted, dashed, solid, and dash-dotted lines correspond to periods of 400, 500, 600, and 700 s, respectively. The effective viscosity is 2.4 × 10¹⁴ cm² s^-1, V_A = 130 km s^-1, c₀ = 175 km s^-1, the magnetic field is B₀ = 1.5 G, and the initial wave amplitude (longitudinal velocity u) is 20 km s^-1.