Abstract:
Based on an estimated solar wind condition around 1–2 September 1859, we were able to reproduce the Carrington magnetic storm magnetometer record, with the H-component depression of −1600 nT, made at Colaba Observatory in Mumbai, India. We used an updated Dst prediction model from Temerin and Li (2002), which provides a prediction efficiency of 0.91 for 1995–2002 interval using a fixed set of modeling parameters. The negative depression in the magnetometer record could be explained by assumptions as to the condition of the solar wind that, though far more geoeffective than any that have ever been observed, do not seem improbable given the known average speed of the interplanetary shock for this event. The extremely fast recovery of the magnetometer record, however, required that the dynamic pressure of the solar wind also be substantially larger than has ever been observed. We also showed how the strength of the magnetic storm would have depended on the season and the time of day. For the same solar wind conditions in GSM coordinates, the largest magnetic storms occur around the fall equinox and at the time of day when the dipole axis is most perpendicular to the solar wind velocity. Given the assumed very fast solar wind with a very large negative interplanetary magnetic field (IMF) Bz directly impacting the Earth, our model together with the known magnetometer record indicates that a super magnetic storm with minimum Dst less than −1600 nT could have occurred and thus can occur again. For the magnetic storm of 1–2 September 1859, however, the extremely fast recovery of Dst requires an extremely large pressure enhancement. This suggests that this particular event was doubly unusual.
