A New Approach To The Theory Of Geomagnetic Dynamo

Now several decades later after publication of work about magneto rotation instability (MRN, Velikhov E.P. JETP,vol. 36, pp 1399--1404, 1959), recent years witnessed dramatic progress in understanding of how turbulence arises and transports angular momentum in astrophysical accretion disks. The instability occurs when outwardly decreasing differential rotation takes place generating magneto hydrodynamic turbulence. As a result a greatly enhanced effective viscosity appears, the origin of which had been a long standing problem. The nature of the MNR can link two subfields of magnetized fluid research: accretion theory and dynamos, the assumptions of classical dynamo theory meaning break down in accretion disks. The study of MNR experimentally with liquid sodium was done in spherical geometry intended originally for study of the theory of a geomagnetic dynamo. It was shown that in absence of gradients of temperature i. e., convection so important for the traditional theory of a geomagnetic dynamo, generation of a magnetic field was obtained due to development MRN. It allows to propose a new mechanism of geomagnetic dynamo where the basic role plays MRN, describing not only occurrence of magnetic field of the Earth, but also its evolution in time. The last seismological measurements giving persuasive evidence that the real core is spinning faster than the rest of the Earth enables us to describe phenomenologically the development of nonlinear regime of MNR and predict the correlation between the evolution of magnetic field and that of differential rotation of the inner core and the mantle.