On the 60-year signal from the core

The decadal variation in the length of day and in the Earth's magnetic field is analyzed by empirical mode decomposition (EMD). The existence of a periodicity of about 60-years in the Earth's angular velocity has often been inferred and is confirmed here, with a new estimate of approximately 62 years. The existence of a similar periodicity in the geomagnetic field has been controversial. From the time series analyses presented here of the magnetic declination at 10 observatories, it is concluded that a geomagnetic periodicity of about 62 ± 3 years does exist. A similar analysis of the magnetic inclination at five observatories gives a period of 58 ± 5 years. The declination data from four observatories is found to correlate with the length of day signal, with a correlation coefficient of approximately 0.6.