Intradecadal variation in Earth’s length of day – the link to geomagnetism

Recently, we have demonstrated that intradecadal variations in length-of-day for the last 50 years can be well explained by a simple approximately 6-year oscillation, broadly constant in amplitude and phase. There is also some evidence that this variation may also be present in earlier records. There is a strong correlation with changes in the geomagnetic record, both with geomagnetic jerks and the recently defined geomagnetic pulses. This correlation poses a strong constraint on mantle electrical conductivity, and therefore the structure and composition of the deep mantle.