Bayesian approach for auroral oval reconstruction from ground-based observations

Abstract

To understand long term variability of solar activity, homogeneous time series are required. However, proxies like the Zurich sunspot number or cosmogenic isotopes suffer from discontinuities. Naked eye observations of aurorae, however, might be used to bridge discontinuities in solar activity indices in order to approach a homogeneous solar activity record. With information derived from aurora observations like observing site, time of aurora sighting and position on sky we can reconstruct the auroral oval. Since aurorae are correlated with geomagnetic indices like the Kp index, it is possible to obtain information about the terrestrial magnetic field in the form of the position of the magnetic poles as well as the magnetic disturbance level. \\ Here we present a Bayesian approach to reconstruct the auroral oval from ground-based observations by using two different auroral oval models. With this method we can estimate the position of the magnetic poles in corrected geomagnetic coordinates as well as the Kp index. The method is first validated on synthetic observations before it is applied to four modern geomagnetic storms between 2003 and 2017 where ground-based reports and photographs were used to obtain the necessary information. We have shown that we are able the reconstruct the pole location with an accuracy of $\approx 2^{\circ}$ in latitude and $\approx 11^{\circ}$ in longitude. The Kp index can be inferred with a precision of one class. \\ The future goal is to employ the method to historical observations.