Small-scale velocity field at the Core-Mantle Boundary constructed from the gufml global model

The aim of this study is to construct the fluid flow at the Earth’s Core–Mantle Boundary (CMB). We employ the global “gufm1” model which describes the dipolar geomagnetic field for the last 400 years. We work under the frozen–flux approximation. Using the continuity of the radial component of the geomagnetic field (B_r) component through the CMB, we obtain the respective equation. The two-dimensional velocity field at the CMB is separated into toroidal and poloidal parts. Then these parts as well as the radial component of geomagnetic field and its secular variation are expanded in spherical harmonics series and are substituted in the induction equation. Straightforward calculations lead to a system of algebraic equations. Due to reliability, we use spherical harmonic coefficients and their time derivatives for the period 1850-1986. We obtain the maps of the velocity field as well as the respective maps of the changes of first and second order of the velocity. Generally the changes of in the velocity field span time-scales of the order of decades suggesting a possible connection with the secular variation of the geomagnetic field.