Alfvén frequency
= Alfvén frequency
{c}
{title2=$\omega_a=\mathbf k\mathbin\cdot\mathbf B/\sqrt{\mu_0\rho}$}
The Alfvén frequency is the frequency of an <Alfvén wave> with <wavevector> $\mathbf k$ in a uniform <magnetic field> $\mathbf B$ and <mass density> $\rho$. For a vertical field and vertical <wavenumber> $k$, its square is $\omega_a^2=k^2B_z^2/(\mu_0\rho)$. Its competition with orbital shear determines the <ideal magnetorotational dispersion relation>.