Observational estimate of magnetic field and geodynamo parameters under the surface of the Earth’s core

For the first time, estimates (averaged in latitude and longitude) of the radial derivatives of the vortex magnetic field hidden directly under the surface of the Earth’s core were obtained on the basis of contemporary determinations of the electric conductivity and systematic observations of the geomagnetic dipole evolution, as well as Faraday’s and Ohm’s laws. This allows one to formulate the simplest, ‘almost dipole” model of the vortex field under the core surface and to estimate a characteristic scale of the field measurements, which determines the depth of the adequacy area of the proposed simplest model. According to this estimate, the spatial size of the field (around 60 km) is an order of magnitude less than its typical size, following from an extrapolation of the observable field to the mantle–core boundary. This agrees well with the modern theory of hydromagnetic dynamos of planets, making it possible to refine the typical values of the magnetic field, the convection rate, and specific power, together with other geodynamo parameters, on the basis of known scaling laws and observations. The proposed new approach to determining the surface characteristics of the vortex magnetic field hidden in the interior of a physical object from the observed evolution of the potential field may be used for both astrophysical and engineering objects with an inaccessible current system.