Unexpected variations found in Earth’s rotation

New Scientist : Earth’s rotation is known to vary periodically because of the flow of the oceans and the fluid nature of the mantle and outer core. The result is several overlapping cycles of the lengthening and shortening of days. Using 50 years of GPS and astronomical data that recorded those patterns, Richard Holme of the University of Liverpool, UK, then removed the known cycles to try to uncover other variances in day length. The result was a collection of nonregular jumps that interrupted the regular cycles by a fraction of a millisecond for several months at a time before returning to normal. Three of the jumps occurred in the past 10 years. Satellite recordings of Earth’s magnetic field from the past 20 years revealed that the new rotation variations coincided with variations in the magnetic field. Holme believes that both events could be caused by parts of the outer core temporarily sticking to the mantle, which would explain the suddenness of the changes.