= Magnetostrophic balance
{title2=$2\rho\Omega\hat z\times u=-\nabla p+f_b+J\times B$}
The leading force balance in a rapidly rotating conducting fluid when inertial and viscous forces are small, while <Coriolis force>, <pressure>, <buoyancy> and <Lorentz force density> remain significant. The <Rossby number> and <Ekman number> measure the omitted inertia and bulk viscosity. Rotation does not balance an arbitrary magnetic torque: impenetrable axisymmetric boundaries impose the <Taylor constraint>. Magnetic diffusion can remain in the induction equation even when viscosity is neglected in momentum balance.
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