Auroral oval long-term changes linked to secular variations in earth’s magnetic field and geomagnetic activity

Abstract

Changes in the Earth’s magnetic field and in geomagnetic activity through solar wind conditions can both deeply modify the auroral ovals, which are the regions of most frequent precipitation of energetic particles causing aurora. These two auroral change drivers present long-term trends: the well-known magnetic field secular variation, and the Gleissberg cycle of solar and geomagnetic activity that can also be considered as a secular variation. In this work, both induced long-term changes are compared by estimating the variations in the auroral zone boundaries and area as a consequence of each one acting independently during the period 1932-2022. That is the last 9 decades, which is the period covered by Kp geomagnetic activity index availability. In the first case, the IGRF is used to estimate the timeevolution of the zone enclosed by the fixed geomagnetic latitudes typical for auroral boundaries during quiet geomagnetic activity levels considering steady interplanetary conditions and assuming scaling relations for a purely dipolar field. In the second case, under fixed Earth’s magnetic field conditions, a Kp-based model is used considering an 11-year running mean of this index in order to filter out short-term variations typical of geomagnetic activity. A comparative analysis is then made between the auroral ovals modifications over these last 9 decades.