Alfvén velocity
= Alfvén velocity
{c}
{title2=$\mathbf v_a$}
The <Alfvén velocity> is the signed vector $\mathbf v_a=\mathbf B/\sqrt{\mu_0\rho}$, whose magnitude is the <Alfvén speed>. It follows the orientation of the <magnetic field>, unlike the nonnegative scalar <speed>.