Polar confinement of the Sun's interior magnetic field by laminar magnetostrophic flow

摘要: The global-scale interior magnetic field needed to account for the Sun's observed differential rotation can be effective only if confined below convection zone in all latitudes, including polar caps. Axisymmetric nonlinear MHD solutions are obtained showing that such confinement brought about by a very weak downwelling flow U~10^{-5}cm/s over each pole. Such is consistent with helioseismic evidence. All three components of decay exponentially altitude across thin "magnetic layer" located at bottom tachocline. With realistic parameter values, thickness layer ~10^{-3} radius. Alongside baroclinic effects and stable thermal stratification, take into compositional stratification helium settling layer, present as today's Sun, small diffusivity through hydrogen, chi. value chi relative produces double boundary-layer structure which "helium sublayer" smaller vertical scale sandwiched between top rest layer. Solutions using both semi-analytical purely numerical, finite-difference techniques. confinement-layer flows magnetostrophic excellent approximation. More precisely, principal force balances Lorentz, Coriolis, pressure-gradient buoyancy forces, accelerations viscous forces negligible. This despite kinematic viscosity being somewhat greater than We discuss how layers pole might fit global dynamical picture solar That picture, turn, suggests new insight early Sun longstanding enigma lithium depletion.