Lefèvre, Laure

Talk presented at SouthWest Research Institute , Boulder, CO, USA on 2017-09-15

Abstract: I will present an original historical analysis of Sun-Earth connections in the context of the most extreme space weather events of the last 150 years. To identify the key-factors leading to these extreme events, we have selected a sample of the most important geomagnetic storms based on the well-known aa index. Here we focus on characterizing the active regions most probably responsible for these major geomagnetic storms. For this purpose, we use detailed sunspot catalogs as well as solar images and drawings. For geomagnetic events during the SOHO era, vast amounts of detailed solar data is readily available and thus solar terrestrial connections easy to access through various detailed studies. Events posterior to the 1940s are still relatively easy to study because mainly of the availability of flare data and numerous solar drawings. However, back to the beginning of the aa index in 1868, solar data from catalogs become scarce as well as sunspot drawings. In this study, we have systematically gathered the most interesting sunspot parameters back to 1868, going as far as hunting solar drawings from the old Greenwich archives, and extracting the parameters ourselves. Here we present an analysis of the active region parameters preceding these extreme geomagnetic events at the Sun.