Hydromagnetic dynamos at the low Ekman and magnetic Prandtl numbers

Hydromagnetic dynamos are numerically investigated at low Prandtl, Ekmanand magnetic Prandtl numbers using the PARODY dynamo code. In all the investigatedcases, the generated magnetic fields are dominantly-dipolar. Convection is small-scaleand columnar, while the magnetic field maintains its large-scale structure. In this studythe generated magnetic field never becomes weak in the polar regions, neither at largemagnetic Prandtl numbers (when the magnetic diffusion is weak), nor at low magneticPrandtl numbers (when the magnetic diffusion is strong), which is a completely differentsituation to that observed in previous studies. As magnetic fields never become weak inthe polar regions, then the magnetic field is always regenerated in the tangent cylinder.At both values of the magnetic Prandtl number, strong polar magnetic upwellings andweaker equatorial upwellings are observed. An occurrence of polar magnetic upwellings iscoupled with a regenaration of magnetic fields inside the tangent cylinder and then with anot weakened intensity of magnetic fields in the polar regions. These new results indicatethat inertia and viscosity are probably negligible at low Ekman numbers.