On geomagnetic variations during the August–September storms of 1859 Original Research Article

Hourly magnetic readings of H and D from six geomagnetic observatories in Finland and Russia were utilized for analysis of the time behavior of the extreme space weather event of August/September 1859. The observatories cover about 200° in longitude and magnetic latitudes 45–60°N. The August/September 1859 event consisted of two consecutive magnetic storms that started on August 28th and September 2nd, respectively. The latter and stronger is known as the “Carrington storm”. The August 28–29 storm was greatest at high latitudes (Sitka; magn. lat. 60°N) where field variations (D) of ±700 nT were recorded. On September 2 05–07 UT, exceptionally great magnetic disturbances occurred simultaneously worldwide. The largest magnetic field excursions were about 1500 nT (in D) in a few hours. The disturbances (mainly positive) in H have clearly been even greater but the variometers went off scale. The maximum time derivative of the field was estimated to be about 30 nT/s. During the Carrington storm on September 2 (05–07 UT) the observatories were well inside the auroral oval and the disturbances (mostly positive) registered were connected with eastward flowing auroral electrojets and field-aligned currents. No magnetic signatures of the ring-current can be seen in the observations. However, simultaneous magnetic variations at the Colaba observatory (magn. lat. 10.5°N) near the Equator showed a deep depression (about −1600 nT) in H mostly due to ring-current effects.