Magnetic flux expulsion from the core as a possible cause of the unusually large acceleration of the north magnetic pole during the 1990s

• Published in: Journal of Geophysical Research
• Main Authors: Chulliat, A., Gauthier, Hulot, R. Newitt, L.
• Other Authors: Institut de Physique du Globe de Paris (IPGP), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS), Boreal Language and Science Services, Ottawa, Ontario, Canada.
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2010
• Subjects: [SDU]Sciences of the Universe [physics]; New Siberian Islands; North Magnetic Pole
• Online Access: https://hal-insu.archives-ouvertes.fr/insu-01288849; https://hal-insu.archives-ouvertes.fr/insu-01288849/document; https://hal-insu.archives-ouvertes.fr/insu-01288849/file/jgrb7143.pdf; https://doi.org/10.1029/2009JB007143

International audience The north magnetic pole (NMP) has been drifting in a north‐northwesterly directionsince the 19th century. Both local surveys and geomagnetic models derived fromobservatory and satellite data show that the NMP suddenly accelerated during the 1990s.Its speed increased from about 15 km/yr in 1989 to about 60 km/yr in 2002, after which itstarted to decrease slightly. Using a Green’s function, we show that this acceleration ismainly caused by a large, negative secular variation change in the radial magnetic field atthe core surface, under the New Siberian Islands. This change occurs in a region of thecore surface where there is a pair of secular variation patches of opposite polarities, whichwe suggest could be the signature of a so‐called “polar magnetic upwelling” of the typeobserved in some recent numerical dynamo simulations. Indeed, a local analysis of theradial secular variation and magnetic field gradient suggests that the secular variationchange under the New Siberian Islands is likely to be accompanied by a significant amountof magnetic diffusion, in agreement with such a mechanism. We thus hypothesize thatthe negative secular variation change under the New Siberian Islands that produced theNMP acceleration could result from a slowdown of the polar magnetic upwelling duringthe 1990s. We finally note that the NMP drift speed is determined by such a combinationof factors that it is at present not possible to forecast its future evolution