CORONAL MASS EJECTIONS AND THE CARRINGTON EVENT

Anthony G Williams

This is a modified version of an article originally posted on my SFF blog in July 2009

If global warming plus the possibility of a major asteroid strike aren't enough to worry about, there's another threat to our civilisation: coronal mass ejections (CMEs). These occur when storms on the surface of the sun throw out plasma balls, which fly through space at high velocity and occasionally connect with the Earth. They were in the news early in 2011 because the sun is at the start of an active phase when large numbers of storms occur. Some CMEs struck the Earth soon after, causing spectacular night-time Northern Lights (aurora borealis) to be visible much further south than usual.

They can cause a lot more than this. CMEs vary a lot in size and small ones are common and relatively harmless, but if a giant one hits the Earth, we are in trouble deep. This is no idle threat, as was made clear in the New Scientist magazine of 23rd March 2009 in an article on the potential impact of CMEs, based on a report funded by NASA and issued by the US National Academy of Sciences (NAS) in January 2009. Such a giant event happened in 1859, as described by the British astronomer Richard Carrington. This caused stunning auroras even at equatorial latitudes and severely disrupted telegraph networks. The consequences of an event on a similar scale today would be far worse.

Our problem is that in the 150 years since the Carrington event we have become much more vulnerable to its effects. Satellite communication and navigation systems in the CME's path would be fried. Much worse, the long cable lines of our electricity grids would act as aerials, capturing the plasma and focusing it on the transformers which convert the high-voltage grid supply to lower voltage domestic supplies. The massive flow of DC current would overheat and melt the transformers' copper wiring, effectively destroying them. Power supplies in the area hit by a large plasma ball would fail. A small-scale version of this happened in Quebec province in March 1989, and six million people were without electricity for nine hours. A giant strike the size of the Carrington event would be orders of magnitude worse.

The NAS report outlines the consequences if a Carrington event hit the USA. Within 90 seconds, 300 key transformers would be knocked out, cutting off power to 130 million people. All kinds of electronic communications would fail. Within a few hours, water taps would run dry as there would be no power to pump the supply. All electrically-powered transport would grind to a halt. So would petrol and diesel vehicles as their tanks ran dry, because there would be no power to pump fuel at the filling stations. With no transport, supplies of food in urban areas would rapidly run out; typically, cities only have about three days' supply of food (and much of that is in freezers or refrigerators, so would soon spoil). Even establishments with backup generators, such as hospitals, could only keep going for as long as their fuel lasted probably three days. Medicines would soon begin to run out, as the factories would have no power to make them and the vehicles no fuel to transport them.

Worst of all, it would take a very long time to put matters right. The wrecked transformers would have to be replaced, a job which takes a skilled crew at least a week for each one assuming they have a spare one handy. There are very few spare ones lying around; they are usually made to order, a process which can take a year. And the factories which can make them will probably have no power or, if they are outside the affected zone, problems in transporting them to where they're needed. Even with the transformers repaired, there would be a kind of Catch-22 because almost all the natural gas and fuel pipelines which supply power stations require electricity to operate. No electricity = no fuel = no electricity. Coal fired power stations may have 30 days of fuel, but nuclear ones would automatically shut down when the grid fails.

Given the difficulties and delays in responding to and recovering from Hurricane Katrina, an event which affected only a very small percentage of the USA, it is easy to see that rescue and recovery services would be completely overwhelmed by a national disaster on such a scale. The net result of all this, according to the NAS report, is that the recovery time would be four to ten years and the USA may never be the same again. The New Scientist article quotes an estimate of the death toll of "tens of millions of lives". The rest of the developed world is just as vulnerable to a major geomagnetic storm as the USA. Ironically, it is the poorest and most rural societies which would be least affected.

In the past, solar satellites were only capable of giving a few minutes warning that a CME was on the way. However, a follow-up report in the 11th April 2009 issue of the New Scientist described a new technique for predicting CMEs using NASA's STEREO (Solar Terrestrial Relations Observatory) pair of spacecraft which follow the same orbit as the Earth. A check following a small CME event of 16 December 2008 discovered that STEREO spotted changes to the sun which presaged the event. Given some improvements to the software to speed up data analysis, up to 24 hours warning could be provided of a CME about to head our way. Such long-term warnings have already happened in 2011.

Such advance warnings are essential to prepare for Carrington events. Precautions to protect the grid could then be taken, such as adjusting voltages and loads and restricting energy transfers - provided that the supply companies have such procedures in place and well-practiced. As a back-up to this, physical modifications to the grids might also be made in order to protect transformers from such massive surges with over-current relays which would fail before the transformers were damaged; blackouts would still occur, but recovery would be a lot faster. Such a programme of modifications would be costly, however, so governments would probably have to pay private sector suppliers to do this.

Let's hope that someone is working on a system for automatic warnings to be sent to power grid organisations worldwide and that those organisations are compelled to put in place and rehearse the precautionary measures, with government funding for more extensive passive protection measures. The consequences of failing to do so could be catastrophic.

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