Acoustic waves, or sound waves, are longitudinal waves that need a material medium to propagate. Acoustic waves create pressure gradients in the medium as they travel through it.  In a plasma the speed of sound waves is

γ = ratio of specific heats in an ideal gas
T = temperature
k = Boltzmann’s constant

There are two types of magnetic waves but they do not exist independently of each other. Alfvén waves are transverse magnetic waves that travel along a magnetic field line like a wave travels along a plucked string.  The speed of Alfvén waves is

B = magnetic field strength
μ = permeability constant
ρ = particle density

Magnetosonic waves are longitudinal magnetic waves that propagate perpendicular to magnetic field lines. They create magnetic pressure gradients as they travel across the magnetic field.

Usually we discuss electromagnetic (EM) waves by describing the oscillating electric field. But we know that EM waves also have a magnetic field that oscillates perpendicular to the electric field.

So, if Alfvén and magnetosonic waves are magnetic waves, it's probably not surprising that they have an electric field that oscillates perpendicular to the magnetic wave. This is one mechanism that allows magnetic waves to drive acoustic waves. Here is a diagram of how this might happen: It is described below.

As a magnetic wave propagates through a plasma, the electric field creates pressure gradients in the plasma (i.e. in the “gelatin”). These pressure gradients in the gas of the plasma oscillate and are therefore acoustic waves.

Another possible mechanism involves the velocity pertubations to the magnetic field. Magnetic field perturbations are also perturbations to the gas because this wave is in a plasma and the gas moves with the magnetic field. In both cases, when the wave is in a ß~1 plasma, the perturbations to the gas cause oscillating pressure gradients that can decouple from the magnetic field and continue to exist and propagate as acoustic waves.

 

Next: Does ß=1 anywhere in Earth’s atmosphere?

 

How are aurorae created?
Can we hear the aurorae?
Wave transformation on the Sun
What is ß?
How can a magnetic wave transform into an acoustic wave?
Does ß=1 anywhere in Earth’s atmosphere?
Continuing research
Bibliography