An Update on the Centered and Eccentric Geomagnetic Dipoles and Their Poles for the Years 1980?￠????2015

摘要

This paper is an update and extension of an earlier study of the centered and eccentric dipole models of the Earth's magnetic field. We use the 1980?￠????2015 IGRF Gauss coefficients to recalculate the magnetic dipole moments and pole positions for both the centered and eccentric dipoles for an additional 35????years. The changes that have taken place are mostly extensions of the trends described earlier. Interestingly, the earlier weak suggestion of an accelerated decline in the magnetic moment over the interval 1975?￠????1985 persists in the more recent data; if the current decline for the years 2000?￠????2015 continues, the Earth's field is projected to decline to nothing around the year 3797????A.D. This projected decline to zero field will almost certainly not occur on this date, but it is of interest because the timescale for the decline is remarkably short compared with the timescales derived for past field reversals. The asymmetry of the Earth's field continues to increase quite rapidly, with the offset of the equivalent dipole from the Earth's center now close to 9% of the Earth's radius. Since we now know that all the planets in our solar system with global magnetic fields have asymmetric fields that can be modeled more accurately as eccentric dipole fields, and not as centered dipole fields, the eccentric dipole analysis reported here can now be viewed more generally as an approach to planetary magnetic fields and not just to the magnetic field of our own planet.