Extreme Geomagnetic Field Variations: Historical Measurements, and Modern Simulations

Abstract:

Much work has been performed studying extreme geomagnetic storms, with their potential to damage and disrupt grounded infrastructure. Examples of these storms include the March 1989 event, the 2003 Halloween storms, and perhaps most extreme of all, the 1859 Carrington event. Thankfully, storms of this magnitude are relatively rare. When considering geomagnetic field data availability, the rarity of these events becomes a problem however. Although geomagnetic field observatories have been operating since the 1830s, widespread high-cadence (60s) digital data are only readily available since the 1980s, meaning few examples of extreme geomagnetic storms have good coverage. Recent work has carefully analysed analogue geomagnetic field measurements (as well as auroral sightings) for a number of superstorm events, expanding our understanding of the scale and frequency of extreme geomagnetic storms.

In this talk, I will discuss recent examples of digitising 19th and early-20th century geomagnetic field measurements, including a dataset from Rome during the Carrington event which hints at the extent of the auroral oval. In addition, I will outline our recent attempts to recreate aspects of these extreme storms using the Space Weather Modeling Framework. By tailoring the solar wind inputs for these magnetohydrodynamic simulations, aspects of these old geomagnetic field measurements can be recreated, allowing for a more informative study of extreme historical events. Examples of this include estimating the equatorward extent of the auroral oval for 'Carrington-scale' (i.e., Dst < -1000 nT) events, as well as the famous rapid dip and recovery of $B_H$ measured at Colaba during the Carrington event.