Reconstructing Extreme Space‒Weather Events in History

Abstract:

Studies of extreme space‒weather events are important in the modern world, due to the impacts of such extreme events on any civilization that is increasingly depending on the technological infrastructure. The most extreme space‒weather event ever recorded is arguably the Carrington event in 1859, both in terms of the amplitude of the associated magnetic disturbance and the equatorward extension of the auroral oval. However, it is not immediately clear what kind of position the Carrington event occupies in comparison with other extreme space‒weather events. Here, we evaluated the strength of the extreme space weather events in 1770, 1872, and 1921 in terms of the equatorward boundary of the auroral oval (auroral emission region) on the basis of eyewitness auroral records, in order to compare them with one another. Our studies indicate that the reconstructed auroral oval for the Carrington event is comparable to the reconstructed auroral ovals for these extreme events. Here, we concentrate our discussions on the records with information about elevation angle of the auroral display. As a result, the strength of the magnetic storm, in terms of the equatorward boundary of the auroral oval (auroral emission region) in the Carrington event is comparable to those of the events in 1770, 1872, and 1921. This result indicates the importance of further analyses on the correlation between the intensity of the magnetic disturbance and the equatorward extension of auroral oval in extreme space‒weather events, and further comparisons with theoretical analyses on the frequency of extreme events.