 Equal-diffusivity interface dynamo

An ideal planar alpha-Omega dynamo places poloidal regeneration above an interface and shear-generated toroidal induction below it. With equal constant diffusivities, decay away from the interface and ordinary electromagnetic matching, its surface-wave branch grows when $D>32$ for positive $k,\alpha ,V$. The model separates the two regeneration regions while allowing diffusive coupling. The threshold refers to this model, not every solar interface dynamo or a full isotropic alpha closure.