An estimation of the Carrington flare magnitude from solar flare effects (sfe) in the geomagnetic records

The aim of this work was to derive a method of estimating the size of a solar flare from the related magnetic variation, or solar flare effect (sfe), observed at magnetic observatories. The particular goal was to re-assess the Carrington flare, which occurred at 11.15 UT on 1st September 1859. We review previous work to estimate the flare magnitude and re-examine observations of the sfe on the Kew and Greenwich (both London area) observatory magnetograms, recovered from the BGS archives. We correlate recent flares of known X-ray flux against the related sfe, taking into account location at the time of the event and use this relationship to estimate the size of the Carrington flare.