Study On Magnetic Field And Flow Structures In ABC-dynamo

Dynamo theory describes the magnetic field induced by the rotating,convecting and electrically conducting fluid in a celestial body.It is so far the most widely accepted theory to explain the production of the geomagnetic field.Though most problems have been solved since the theory is proposed,the mechanism of the dynamo is still not fully understood by people.Under such a background,a model so called ABC dynamo which has the fast dynamo action in dynamo theory is studied in the paper.Spectral method is used in the numerical simulation.After verification of the reliability,the evolution of the magnetic energy under high-symmetric situation is analyzed.And it is found that the oscillation of energy is due to the turnover of the magnetic field.Further studies of the magnetic structures enable us to illustrate the turnover process and raise the concept of the principle magnetic structures.Later,during the study of the critical situation,it is found that the principle magnetic structures no longer exist and the turnover pattern also changes.During the analyze of flow field,Lagrangian coherent structures(LCSs)are introduced through Finite-time Lyapunov exponents(FTLE).On this basis,skeleton structures of the flow field is also proposed in this paper.It is found that this kind of structures has strong relations with the distribution and evolution of magnetic energy.In the high-symmetric model,strict geometric relations is found between the skeleton structures and magnetic structures.Though these relations will change with the parameters,the distribution of the magnetic structures still has close link with the stagnation points and LCSs.