The Largest Magnetic Storm on Record...or is it?
The 'Carrington Event' of August 27th to September 7th, 1859 was recorded at the time by analogue magnetometer systems directly onto photographic paper at Greenwich Observatory, London
Declination, or compass direction east of true north (D), is the lower trace on each image and the horizontal force (H) is the upper trace. Universal Time is the time recorded here (astronomical) plus 12 hours and measured D precedes H by approximately 12 hours.
This is one example of the historical data contained in the British Geological Survey geomagnetic archives. We have digistised our complete collection of over 250,000 magnetograms and these are now available to view freely online. In this archive you will find that the Carrington Event was also recorded at the Kew Magnetic Observatory in west London. Greenwich and Kew magnetic observatories were ultimately replaced by more modern and more remote observatories elsewhere in the UK, during the 20th century, to minimise electromagnetic interference.
Please note that these timings are approximate and should not be regarded as definitive. Also note, the size and scale of each image is only approximately similar, day-to-day. Some data have also been lost, either due to ink and paper degradation, or because the variations were so large they were off-scale and therefore unrecorded. These images are also described in an accompanying poster: The Largest Magnetic Storm on Record - Carrington Event 1859.
In these images, a very clear solar flare effect, a short-lived geomagnetic 'pulse' caused by enhanced electrical currents that were created high in the atmosphere by an intense solar flare, is recorded in H as beginning at 23:15 on August 31st. But this actually occurred at 11:15 Universal Time (or Greenwich Mean Time) on September 1st. The solar flare effect was measured as 110 nT in H and 0.283 degrees in D.
This flare was the first recorded as being observed by telescope, in this case by British astronomer Richard Carrington at Redhill in Surrey (and corroborated by an independent observation made by another British astronomer, Richard Hodgson). The flare and subsequent severe geomagnetic storm, which began just 17.6 hours after the solar flare effect, bear Carrington’s name. The storm was the result of an intense coronal mass ejection (CME), associated with the flare. To get here in that time, the CME must have travelled at over 2300 kilometres per second, or over 5.2 million miles per hour.
A scientific paper puts the Carrington Event into context, compared to other notable magnetic storms of the last 150 years. The Table to the right also shows the top 21 geomagnetic storms in our UK magnetogram archive and online digital data, according to a standard measure of geomagnetic field activity. (* We include Carrington as the #1 storm, though the aa index only commenced in 1867.)
