Observed Auroral Ovals Secular Variation Inferred from Auroral Boundary Data

We analyze the auroral boundary corrected geomagnetic latitude provided by Auroral Boundary Index (ABI) database to estimate long-term changes of core origin in area enclosed this during 1983–2016. design a four-step filtering process minimize solar contribution temporal variation for northern and southern hemispheres. This includes activity effects, removal high-frequency signal, additional ~20–30-year dominant periodicity. Comparison our results with secular change plus polar cap areas obtained using simple model magnetosphere field reveals decent agreement, increase/decrease southern/northern hemisphere respectively both observations model. encouraging agreement provides observational evidence surprising recent decrease zone area.