Variation in the rotation rate of the earth and the geomagnetic field

In its first part this work focuses on connection of length of day (LOD) with centered and eccentric geomagnetic dipole fields described with the use of Gaussian coefficients derived from global geomagnetic observations is discussed for the epoch 1900–2000. The statistical comparison of temporal variation of earth magnetic and astronomical data shows close correlation of geomagnetic dipole momentum M0 and ΔLOD. It should be mentioned that the time-correlation is closer when the centred geomagnetic dipole is used for statistical modelling. In the same time no relation was found between ΔLOD and the orientation variations of the geomagnetic dipole.In the second part of present study the connection of geomagnetic field and the LOD is investigated in geological time-scale. A significant ΔLOD was found which coincides in time with the geomagnetic Mesozoic low. The reason of this coincidence is enigmatic.