Recently I read a post on Facebook about the Carrington Event, a massive , powerful solar storm that hit the Earth 159 years ago on 2 September 1856.
In the post, which appears to have been written in 2012 as it opens with the statement “156 years ago; a geomagnetic storm:“, the author recites some of the effects from the storm including: “On Sept. 2nd, a billion-ton coronal mass ejection (CME) slammed into Earth’s magnetic field. Campers in the Rocky Mountains woke up in the middle of the night, thinking that the glow they saw was sunrise. No, it was the Northern Lights. People in Cuba read their morning paper by the red illumination of aurora borealis. Earth was peppered by particles so energetic, they altered the chemistry of polar ice.
Hard to believe? It really happened–exactly 156 years ago. This map shows where auroras were sighted in the early hours of Sept. 2, 1859:
As the day unfolded, the gathering storm electrified telegraph lines, shocking technicians and setting their telegraph papers on fire. The “Victorian Internet” was knocked offline. Magnetometers around the world recorded strong disturbances in the planetary magnetic field for more than a week.“
Then the article provides a little more recent solar history to consider: “The cause of all this was an extraordinary solar flare witnessed the day before by British astronomer Richard Carrington. His sighting marked the discovery of solar flares and foreshadowed a new field of study: space weather. According to the National Academy of Sciences, if a similar storm occurred today, it would cause a trillion dollars in damage to society’s high-tech infrastructure and require four to ten years for complete recovery.
In fact, a similar flare did occur just a few years ago. On July 23, 2012, a CME of rare power rocketed away from the sun. The storm was in all respects at least as strong as the 1859 Carrington event. The only difference is, it missed. no harm done. The July 2012 event serves as a reminder, however, that extreme space weather is not a thing of the past.“
It appears that the Facebook article was compiled primarily from Wikipedia and NASA references and while most of the detail is correct there is one part which is incorrect according to the most recent studies, and that part goes to the heart of the claim that the 2012 Coronal Mass Ejection was as strong as the Carrington Event CME.
In 2013, physicist Daniel Baker of the University of Colorado along with colleagues from NASA and other universities, published a seminal study of the July 2012 storm in the December 2013 issue of the journal Space Weather. Their paper, entitled “A major solar eruptive event in July 2012,” describes how a “powerful coronal mass ejection (CME) tore through Earth orbit on July 23, 2012.”
According to Dr. Baker “…the July 2012 storm was in all respects at least as strong as the 1859 Carrington event, The only difference is, it missed.”
In their Dec. 2013 paper, Baker et al. estimated the Dst (remember that acronym) for the July 2012 storm. “If that CME had hit Earth, the resulting geomagnetic storm would have registered a Dst of -1200, comparable to the Carrington Event and twice as bad as the March 1989 Quebec blackout.”
However, In 2014 a physicist by the name of Pete Riley published a paper titled “On the probability of occurrence of extreme space weather events” in which he “looked carefully at a parameter called Dst, short for “disturbance – storm time.” This is a number calculated from magnetometer readings around the equator. Essentially, it measures how hard Earth’s magnetic field shakes when a CME hits. The more negative Dst becomes, the worse the storm. Ordinary geomagnetic storms, which produce Northern Lights around the Arctic Circle, but otherwise do no harm, register Dst=-50 nT (nanoTesla). The worst geomagnetic storm of the Space Age, which knocked out power across Quebec in March 1989, registered Dst=-600 nT. Modern estimates of Dst for the Carrington Event itself range from -800 nT to a staggering -1750 nT.”
Note that the Atmospheric and Environmental Research group, a highly qualified and influential group of scientists, also mark the Carrington Event at -1750 nT.
Consequently if modern equipment permitted scientists to peg the Dst for the July 2012 solarstorm at -1200 nT, and modern estimates of the Carrington Event are that it was a -1750 nT storm, it quite possible that the 1859 solarstorm is yet to be matched.
One more sobering thought: Riley, by extrapolating the frequency of ordinary storms to the extreme, calculated the odds that a Carrington-class storm would hit Earth in the next ten years.
For more on these two storms and the Carrington Event, here are a couple of good references: