Assuming a magnetic field strength of 500 mT at the surface of the Sun and a density 10E-12 kg/m³ in the corona, we find that the velocity of Alfvén waves is:
v = B/sqrt(µ0 · ρ) = 500E-3/(4πE-7 T · m/A · 10E-12 kg/m³ = 4,460 km/s
This is, of course, a pretty high value: the Sun is a place of violent phenomena and immense forces! Read more