Monochromatic coupled magnetic and velocity response ($D=\nu \eta k^4+(\mathbf{B}\cdot \mathbf{q}{)}^2/({\mu }_0\rho )$)

For a steady forced Fourier mode with $|\mathbf{q}|=k$, coupled viscous and magnetic response gives $\hat{\mathbf{u}}=[\eta k^2\hat{\mathbf{f}}+i(\mathbf{B}\cdot \mathbf{q})\hat{\mathbf{g}}/({\mu }_0\rho )]/D$ and $\hat{\mathbf{b}}=[\nu k^2\hat{\mathbf{g}}+i(\mathbf{B}\cdot \mathbf{q})\hat{\mathbf{f}}]/D$. Their mean-field electromotive force contains both forcing helicities and a possible weighted cross-forcing correlation. Jointly isotropic forcing removes the latter; its vanishing at zero mean field alone is insufficient for anisotropic forcing.