Ambient-controlled interfacial plug current
= Ambient-controlled interfacial plug current
{title2=$u\sim\Delta\rho gH^2/\mu$}
The gravity force per interfacial area is $\Delta\rho gH^2/R$, while ambient viscous <traction> is $\mu u/R$. Their balance gives the radial velocity scale independently of current <viscosity> within the appropriate plug-flow window.