Estimating Maximum Extent Of Auroral Equatorward Boundary Using Historical And Simulated Surface Magnetic Field Data

The equatorward extent of the auroral oval, the region which separates the open-field polar cap regions with the closed field subauroral regions, is an important factor to take into account when assessing the risk posed by space weather to ground infrastructure. During storms, the auroral oval is known to move equatorward, accompanied by ionospheric current systems and significant magnetic field variations. Here we outline a simple algorithm which can be used to estimate the maximum extent of the auroral equatorward boundary (MEAEB) using magnetic field data from ground-based observatories. We apply this algorithm to three decades of INTERMAGNET data, and show how the auroral oval in the Northern hemisphere moves South with larger (more negative Dst) storms. We simulate a number of storms with different magnitudes using the Space Weather Modeling Framework (SWMF), and apply the same auroral boundary detection algorithm. For SWMF simulated storms with Dst > -600nT, the estimates of the MEAEB are broadly in line with the same estimates for historical events. For the extreme scaled storms (with Dst < -1,000 nT), there is considerable scatter in the estimated location of the auroral equatorward boundary. Our largest storm simulation was calculated using Carrington-like estimates for the solar wind conditions. This resulted in a minimum Dst = -1,142 nT, and a minimum estimated auroral boundary of 35.5 degrees MLAT in places.