Upper panel: The largest time derivative of the horizontal ground magnetic field (|dH/dt|) along each meridian (1° separation) in the northern hemisphere as calculated from the simulated Carrington event at 06:10–06:38 UT on 2 Sep 1859. Red dots indicate values exceeding the largest known measured value (2700 nT/min) at the Lovö observatory in Sweden on 13 Jul 1982 and also marked as a dashed line. Lower panel: geomagnetic latitude of the site of maximum |dH/dt| at each longitude. Red colour is used similarly to the upper panel.