The 1859 Space Weather Event Revisited
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Number: | 213 |
1st Author: | Ed Cliver |
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Published: | November 25, 2013 |
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Introduction
After more than 150 years, the space-weather event of 1859 associated with Carrington's name, continues to intrigue and inform us. It was comprehensively observed by many of the most modern tools available at that early time, which of course did not include any of the electronics that we take for granted today. The phenomena observed included the Carrington flare itself, plus various [geomagnetic] processes that (mostly in retrospect) laid the foundation stones for [heliospheric physics] and [space weather]. One of the simplest and most important indices is [Dst], a measure of global geomagnetic variability during a [magnetic storm] such as that associated with the 1859 event.
This "Carrington flare" is doubly intriguing because of its distinction both as the first reported solar flare and, coincidentally, the largest geomagnetic disturbance yet recorded. It is the exemplar and guide for us as regards extreme space-weather events.
Estimates of Event Magnitudes
In a recent paper [Ref. 1], Bill Dietrich and I have reassessed the size of the 1859 event and its consequences. Our best guesses are as follows: a flare magnitude (soft X-ray classification) and total (flare radiation plus CME kinetic) energy of ~X45 and ~5 x 1032 erg, respectively (Figure 1); a >30 MeV proton fluence (F30) of ~1010 cm-2; and a minimum Dst index of ~ -900 nT. These estimates and those measured for the closest modern competitors in each category are shown in tabular form here:
Event GOES Energy PFU Dst erg cm-2 [nT] SOL1859-09-01 X45 1032 1 x 1010 -900 SOL2003-11-04 X35 1033 SOL1972-08-04 5 x 109 SOL1921-05-14 -850
The estimated geomagnetic Dst index for the Carrington magnetic storm, reduced from a reported -1760 nT value based on Colaba (near Mumbai, India) observations, reflects direct (Green and Boardsen, 2006) and indirect (Figure 2) evidence that the Colaba reading included an [auroral] component.
In a related paper ([Ref. 2]) we question the recent attribution of the cosmogenic nuclide event of 775 AD to the Sun (Ref. 3]). Such a solar event would imply an F30 value of ~8 x 1010 cm10-2 (approximately 10 times the value recorded during the three-month interval of sustained strong SEP activity from August-October 1989), a 1 GV proton fluence 45 times larger than that of the February 1956 ground level event, or a single flare with a GOES classification of X230 (1034 erg) flare.
Conclusion
The solar flare and terrestrial effects of the Carrington space-weather event of 1859 are still of great current interest, and the work described here is helping to place it in the context of recent remarkable discoveries. There is a caveat regarding the coincidence of first flare and greatest storm in the 1859 event. Hugh Hudson (personal communication, 2013) cautions that the first flare reported was bound to have been a whopper. That said, there is no guarantee that a big flare will produce a big magnetic storm, since their heliographic position is also crucially important for such effects. The 4 August 1972 flare had a CME with a shorter transit time to Earth than that of the 1859 event (14.6 hr vs. 17.5 hr) but the associated 1972 storm (Dst = -125 nT) does not rank in the top 25 of such events.
References
[1]
[2]
[3] "The AD775 cosmic event revisited: the Sun is to blame"
RHESSI Nugget Date | 25 November 2013 + |
RHESSI Nugget First Author | Ed Cliver + |
RHESSI Nugget Index | 213 + |