Some notes I've collected on the subject. The Carrington Event was by no means the last geomagnetic storm of any consequence, nor was it the worst geomagnetic storm uncovered.
quiet times: between +20 nT and -20 nT
moderate geomagnetic storm: between -50 nT and -100 nT
moderate storm: between -100 nT and -250 nT
geomagnetic super-storm: greater than -250 nT
- current flows are greatly increased in areas that sit directly on rock, the rock prevents current flowing through the earth and instead takes the better flow path through power lines (this is called geomagnetically induced currents)
- long transmission lines (many kilometers in length) are subject to damage by geomagnetically induced currents, this chiefly includes operators in China, North America, and Australia (especially in modern high-voltage, low-resistance lines), the European grid consists mainly of shorter transmission circuits which are less vulnerable to damage
- internet service providers may well go down during geomagnetic storms and remain non-operational long after, so any equipment requiring a working internet connection to function may not work (and that includes some power plant equipment)
- rapidly fluctuating geomagnetic fields can produce geomagnetically induced currents in pipelines, which can cause pipeline flow meters to transmit erroneous flow information
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2005/01/20-Solar activity released the highest concentration of protons ever directly measured
2003/11/04-Halloween Solar Storm series, solar flare rated X28 but some researchers calculated it could have been as high as X45, even at X28 it was the biggest solar flare ever recorded but fortunately it only indirectly affected Earth, before it was over x-rays overloaded the detectors on the Geostationary Operational Environmental Satellites (GOES), a one hour power outage occurred in Sweden as a direct result of the solar activity, the Ulysses (near Jupiter), Cassini (approaching Saturn), and Voyager-2 (so far out it took until April 2004 for the energy to reach it) spacecraft all detected the storm, at least one of the solar storms in the series was compared by some scientists in its intensity to the Carrington Event, researchers from the University of Otago/New Zealand used an indirect method of radio wave-based measurements of the x-rays' effects on the Earth's upper atmosphere to revise the flare's size from a merely huge X28 to a "whopping" X45, the solar flare that knocked Quebec's electrical grid out in August 1989 was "only" a X15-X20 ("minimum Dst values were -151, -353 and -383 nT" - Wikipedia)
2001/04/03-Solar flare rated X20, the same intensity as the flare that took out Quebec's electrical grid in August 1989
2000/07/14-Bastille Day Solar Storm, solar flare rated X5.7, geomagnetic super storm occurred on July 15–17, despite the storm's strength no power distribution failures were reported, this was observed by Voyager-1 and Voyager-2, this was the biggest solar radiation event since the 1989/03/13 Quebec blackout, the proton event was four times more intense than any previously recorded since the launches of SOHO in 1995 and ACE in 1997 ("the minimum of the Dst index was -301 nT" - Wikipedia)
1989/08/16-Solar flare rated X20, this tied 2001/04/02 as the biggest solar flares on record prior to the X28/X45 event on 2003/11/04
1989/03/13-Solar storm rated X15-X20 knocked out Quebec's hydroelectric system and blacked out the entire province for twelve hours and affecting six million people, the Northern Lights were seen as far south as Texas and Cuba, Australian UN troops in Namibia had severe problems with their communications (which depended on HF radio communications), four of the Navy's navigational satellites had to be taken out of service for up to a week ("The minimum of Dst was -589 nT." - Wikipedia)
1921/05/15-Immense solar storm, produced ground currents as much as ten times stronger than the 1989/03/13 Quebec storm, auroras were seen Pasadena/CA and in the eastern US, strongly affected New York state and Europe, ended all communications traffic from the Atlantic Coast to the Mississippi ("The study said a future solar storm like the great magnetic storm of May 1921 would black out most states east of the Mississippi River along with most states in the Pacific Northwest.") ("According to a study by Metatech corporation, a storm with a strength comparable to that of 1921 would destroy more than 300 transformers and leave over 130 million people without power in the United States, costing several trillion dollars.")
1882/11/17-Geomagnetic storm lasted from November 11-26, knocked out some telegraph lines and started a few fires
1859/09/03-Carrington Event, immense solar storm shorted out telegraph wires in the US and in Europe and aurora were seen as far south as Rome, Hawaii (about 20 degrees N), and Cuba, auroras over the Rocky Mountains were so bright, the glow woke campers who began preparing breakfast because they thought it was morning, estimated to be three times the size [also saw as ten times the size] of the 1989/03/13 Quebec solar storm and 50% or more stronger than the superstorm of May 1921, estimated at 200 nT (nano-Teslas) in strength ("The horizontal field was reduced by 1600 nT as recorded by the Colaba Observatory. It is estimated that Dst would have been approximately -1760 nT. - Wikipedia"
0993-0994-"The 993–994 carbon-14 spike was a rapid increase in carbon-14 content from tree rings, and followed the 774–775 carbon-14 spike. This event is also confirmed by a sharp increase of beryllium-10 and hence considered as solar-origin. It may have come from a massive solar storm as a series of auroral observations are known to be observed in late 992."
0774–0775-"The common paradigm is that the event was caused by a solar particle event (SPE), or a consequences of events as often happen, from a very strong solar flare, perhaps the strongest ever known, but still within the Sun's abilities." / "The event of 774 is the strongest spike over the last 11,000 years in the record of cosmogenic isotopes.
