Decade fluctuations in geomagnetic westward drift and Earth rotation

Abstract

Numerous studies of the variations of the Earth's rotation have been made since 1900 (summarized in refs 1, 2). It seems well established that variations in the rotation with periods equal to or less than 2 yr are due to variations in the zonal circulation of the atmosphere2–4. However, there is no general agreement about the cause of the longer-period variations of the Earth's rotation, sometimes known as the ‘decade variations’, although the most favoured explanation is electromagnetic core–mantle coupling (see ref. 5). Several studies6–8 of the correlation between Earth rotation and magnetic field variations have obtained marginally positive results. We have been able to clarify such a correlation over the past 120 yr by studying those magnetic field indicators that are the most sensitive to variations in westward drift of the outer regions of the core. We suggest here that the correlation can be extended back ∼300 yr. Simple models of core–mantle coupling, based on Dullard's ideas, give reasonable quantitative agreement with the observations.