Secular Drift of the Auroral Ovals: How Fast Do They Actually Move?

A surprisingly fast secular drift of the Northern geomagnetic dip pole during the last two decades has attracted much interest lately, in particular, evoking speculations about a possibility of a sweeping relocation of the auroral oval. This letter presents first results of a model investigation of this issue, based on an empirical representation of the distant magnetosphere combined with a series of internal geomagnetic field models for 12 epochs, covering the interval from 1965 to 2020. The secular drift of the northern auroral oval was found to result in its net displacement over the 55-year period, commensurate with the concurrent shifts of the centered, eccentric, and corrected geomagnetic poles, all of them much smaller than the enormous spurt of the northern dip pole. In the Southern Hemisphere, the shift of the auroral oval and of the poles over the same period is much weaker, revealing a remarkable interhemispheric asymmetry. Plain Language Summary The auroral displays associated with space storms occur within two band-like regions, encircling north and south polar caps and called auroral ovals. Aside from highly dynamical reconfigurations of the ovals during space weather events, there exists a much slower and steady shift of their position, associated with a gradual change of the geomagnetic field, termed secular variations and closely related to slow relocation of the geomagnetic poles over the Earth's surface. A remarkable phenomenon observed during the last few decades is an unusually fast shift of the geomagnetic dip pole (a point with strictly vertical field direction) from North Canada toward East Siberia. A natural question is then: how large is the secular shift of the auroral ovals in comparison with the fast relocation of the dip pole? In this work, the problem is addressed from the viewpoint of a magnetospheric model based on spacecraft data. It is shown that the secular shift of the auroral oval between 1965 and 2020 is about the same as that of the geomagnetic dipole axis, which is much slower than the fastly racing dip pole. In the Southern Hemisphere, the oval shifts are much smaller than in the Northern Hemisphere.