Magnetic field stretching at the top of the shell of numerical dynamos

• DOI: 10.1186/s40623-016-0453-x
• Publication Date: 2016-05-13T23:57:52Z
• Authors: Diego Peña; Hagay Amit; Katia J. Pinheiro
• Keywords: Magnetic diffusivity; Downwelling; Magnetic Reynolds number; Secular Variation

The process of magnetic field stretching transfers kinetic energy to and by that maintains dynamos against Ohmic dissipation. Stretching at the top outer core may play an important role specific regions. High-latitude intense flux patches be concentrated flow convergence. Reversed emerge due expulsion toroidal advected core–mantle boundary fluid upwelling. Here we analyze snapshots from self-consistent 3D numerical unravel nature field–flow interactions induces secular variation core. We find shell has a significant influence on despite relatively weak poloidal flow. In addition, locally is often more effective than advection in particular regions field-aligned Magnetic are downwelling dispersed efficient intensifying patches. Both mostly depend Prandtl number Pm. Decreasing Pm gives smaller but stronger stretching. Accounting for both terms suggests Reynolds overestimates actual ratio diffusion ∼50 %. Morphological resemblance between local our dynamo models observed geomagnetic suggest presence Earth’s Our results shed light kinematic origin have implications convective state upper