Magnetic-to-thermal diffusivity ratio
= Magnetic-to-thermal diffusivity ratio
{title2=$\zeta=\eta/\kappa$}
The ratio of <magnetic diffusivity> $\eta$ to <thermal diffusivity> $\kappa$ controls their relative relaxation times. In nonrotating vertical-field <magnetoconvection>, oscillatory linear onset in the simple stress-free layer requires $0<\zeta<1$, so thermal perturbations diffuse faster than magnetic perturbations. This is distinct from the <magnetic Prandtl number>, $\nu/\eta$.