Philip W. Livermore Christopher C. Finlay and Matthew Bayliff
The wandering of Earth’s north magnetic pole, the location where the magnetic field points vertically downwards, has long been a topic of scientific fascination. Since the first insitu measurements in 1831 of its location in the Canadian arctic, the pole has drifted inexorably towards Siberia, accelerating between 1990 and 2005 from its historic speed of 0–15 km yr−1 to its present speed of 50–60 km yr−1. In late October 2017 the north magnetic pole crossed the international date line, passing within 390 km of the geographic pole, and is now moving southwards. Here we show that over the last two decades the position of the north magnetic pole has been largely determined by two large-scale lobes of negative magnetic flux on the core–mantle boundary under Canada and Siberia. Localized modelling shows that elongation of the Canadian lobe, probably caused by an alteration in the pattern of core flow between 1970 and 1999, substantially weakened its signature on Earth’s surface, causing the pole to accelerate towards Siberia. A range of simple models that capture this process indicate that over the next decade the north magnetic pole will continue on its current trajectory, travelling a further 390–660 km towards Siberia.
Historical determinations of the pole position, made for example by Ross in 1831, and later by Amundsen in 1904, relied on ground surveys, searching for the location where the horizontal component of magnetic field H was zero and a mag-netic needle pointed directly down to the centre of the Earth. Such direct determinations are difficult, especially if the pole position is not on land, and because of field fluctuations due to currents in the high-latitude ionosphere. More recently the magnetic pole position has been determined from global models of the geomagnetic field built using measurements made by both satellites and by a network of ground observatories. The accuracy of such pole determinations, which depends on the quality and distribution of the contributing observations along with the ability to estimate the external mag-netic field, has steadily improved over time; since 1999 there has been continuous monitoring of the geomagnetic field from space by a series of dedicated satellite missions, most recently the Swarm mission. In Fig. 1 we show the path of the pole since 1840 from the COV-OBS.x1 (ref. 7) and CHAOS-6-x8 (ref. 8) geomagnetic field models alongside insitu historical measurements. The loca-tion of the magnetic pole is a characteristic of the core-generated magnetic field that is spherically–radially attenuated through the mantle, which may be considered as an electrical insulator on the timescales of relevance here. The magnetic pole’s position is thus only an indirect indicator of the state of Earth’s dynamo. However the specific geometry of the magnetic field on Earth’s surface is of broad societal importance, as was demonstrated by the need for a high-profile irregular update in 2019 of the World Magnetic Model used for navigation in many mobile devices.
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