#Carrington #Level #SolarStorm #CME #space #astronomy
Preparedness is one of those attributes which has been sorely tested in recent times and in many ways has been found wanting but there are many bullets out there with our name potentially on them, one of which we have touched on before, namely solar storms and the CME or coronal mass ejections that usually follow shortly afterwards. These have the potential to create havoc with our modern technological lifestyle, not only affecting satellites but also power generation and all the knock-on effects that losing either of these could bring, one of them even affected the operations of the US navy in the Vietnam war, so I thought that it would interesting just how prepared we are and would it really be as bad as the popular media makes out.
Just as the earth has weather, so does the sun, but on a much, much larger scale and were as our weather systems are restricted to the earth, the suns weather affects the whole solar system and when the sun sneezes in our direction we catch a cold.
The earth is exposed to a continuous stream of energetic charged particles called the solar wind that travel at up to 3.2 Million km/h and flow out into the solar system to well beyond the outer planets.
As these particles are affected by magnetism, some are trapped by the earth’s magnetic field and channelled to the poles where they interact with the oxygen and nitrogen in the upper atmosphere to create the auroras or the northern and southern lights
Now the sun rotates once every 27 days but different areas of the sun rotate at differing speeds, this causes the suns magnetic field to twist and contort.
The sun also goes through cycles of activity approximately every 11 years. During the periods of peak activity, the solar maximum, disturbances on the suns surface called sunspots become much more common. Along with these are more violent disturbances called a solar flares.
If the Flare is powerful enough it will often eject huge quantities of plasma or charged particles that make up the suns surface or corona, these are called Coronal Mass Ejections or a CME’s.
During a solar flare, initially, there is a sudden burst of x-rays and ultraviolet light which reaches earth in about 8 minutes, this interacts with the ionosphere to affect radio communications.
About 30 mins later a flood of high energy electrons and protons travelling at nearly the speed of light hit the Earths magnetic field and any spacecraft that are outsides its protection. This can cause computer errors and failures of electronic circuits causing satellites to glitch or fail and expose astronauts to high levels of ionising radiation. These charged particles are drawn into the magnetosphere and channelled to the poles creating intense auroras that can be seen much farther from the poles than normal.
In the most violent solar flares, huge magnetic loops bulge out from the suns surface that are many times the size of the earth. When these loops break a billion tons or so of plasma are ejected into space, this is the coronal mass ejection. If the Earth is in the wrong place at the wrong time then this along with a part of the suns magnetic field will come barreling through space to hit us in between about 14 to 40+ hours later.
It’s the polarity of the CME’s magnetic field which can do so much damage when it gets to earth. If it is opposite to the earth’s magnetosphere, the two are drawn together just like two magnets, dumping energy all around the earth. If they are the same then they will repel each other and the damage will be much less.
The problem is that CME’s travel at a very high speed and it’s only in the last 15 minutes that we know what their polarity is so that leaves very little time in which to prepare.
When a large CME hits the Earths magnetic field, its a bit like a hammer hitting a bell, the magnetic field rings, compressing and stretching and when a magnetic field lines break the charged particles trapped in it travel back down to the earth creating arouras and inducing electrical currents into the Earths surface and anything running over it like powerlines.
Ones that run north to south, parallel to the Earths magnetic field are the most affected, those that run east to west are less so.
This fluctuating magnetic field can induce DC voltages into the high voltage AC power lines causing the step-down transformers to saturate and overheat and burn out in a matter of seconds. To help protect the transformers against geomagnetically induced currents, giant capacitors that block DC but allow AC to flow are installed. However series capacitors are very expensive and while they may protect one power line, the DC could end up rerouted and concentrated into unprotected lines causing more damage than if capacitors weren’t used.
Although there are backups if too may fail then entire grids can shut down. Because there is much more interconnectivity than ever before with smaller grids sometimes from other countries linked together to form super grids, a shut down in one area could ripple through and cause power outages hundreds to thousands of kilometres away.
CME’s hit the earth all the time with about 2 on average per week but these are small and we bearly notice them. Its when a really big one comes along that we are in for a problem. We have now been watching the sun for long enough to know that the largest the sun can produce would be about 3 times the largest we have seen so far but these are extremely rare, in the order of one every few thousand years.
The first recorded CME to cause us a problem was the “Carrington Event”. A super solar flare seen by the British astronomer Richard Carrington on the 1st Sept 1859. Over the next couple of days there were reports of amazing auroral displays as the northern lights reached as far south as Mexico, Cuba and Hawaii and the Southern lights as far north as Queensland, Australia.
The CME reached the earth 17.6 hours after Carrington saw the initial flare which was quicker than the usual day or two. This is because CME’s sometimes come in a series of bursts with the first usually being smaller but clearing the way of cosmic debris allowing the following ones to arrive faster.
As there was very little in the way of electrical infrastructure at the time, the Telegraph system was the first to show the electrical effects with sparks jumping from switches, shocking the operators and even powering sections of routes when the battery power was removed.
There have been several superstorms since the Carrington event, though none as large but the one which stands out was the March 1989 geomagnetic storm which blacked out large parts of Canada and very nearly blacked out the northeastern United States. This is memorable because it was first have a big impact on our modern infrastructure and it revealed the very real threat that space weather and things like CME’s could have here on Earth.
Since then our power usage has increased but so has our understanding of how solar storms affect us here on earth with much of this data coming from a lucky escape the earth had in 2012, more on that in a moment.
Geomagnetic storms and CME’s are measured using the DST or the Disturbance storm time index, in fact it’s only been since 1957 that we have had proper records of the DST, before then we had to rely on a few magnetometers scattered around the globe.
The DST index measures the ring current around the earth which is created by solar protons and electrons trapped by the Earths magnetosphere. The Ring current produces a magnetic field that protects the lower latitude regions around the equator but is also opposite to the Earths magnetic field, so during geomagnetic storms and CME’s, an increase in the amount of charged particles being trapped here weakens the Earths geomagnetic field.
The DST is measured in NanoTeslas, the lower the negative DST value the weaker the Earths magnetic field and the more the earth is affected by the solar storm.
The typical quite time measurement of DTS is between plus and minus 20nT. An intense geomagnetic storm might decrease that to around -300nT, the Carrington event was believed to have been between -900 and -1750 nT. The reason for this wide range was because of the very limited data that was recorded in 1859 so much of it has to be guestimated from the observations of things like auroras at the time.
Although DST is a good measure for recording events, for measuring realtime changes in the magnetic field like the electrical gid companies need to know, the Kp-index is used. This uses continuous measurements from 13 different measuring stations in the auroral zones around the world. The Kp index utilises a quasi-logarithmic scale of 1 to 9, where 1 is calm, 5 is a solar storm and 9 is an extreme solar storm.
The map above shows you what the Kp-index would be needed to be to see the aurora overhead at a given location.
Now In 2012 we dodged a “Carrington Event” sized bullet when a -1200 nT CME crossed the earth’s orbit, the lucky thing for us was that it was a week late, if it had happened 7 days earlier it would have been a direct hit but it did hit probably the best-equipped satellite for this very issue, the STEREO A solar observatory.
This is one of two nearly identical satellites designed to image the sun and in particular things like solar storms and CME’s. The data collected from this event gave us a huge amount of information and greatly increased our knowledge on how to protect our earth based systems.
Whilst a large CME will be big enough to completely engulf the earth, where you live can have a major impact on how bad the effects could be.
One of the reasons why Canada was affected so much by the 1989 solar storm was that the long stretches of power lines they have, the longer the lines the more electrical energy can be induced into them but it now been discovered that the type of rock the lines run over can also make a big difference.
Its not just metal power cables that the magnetic disturbance can induce power into it’s the ground its self.
In recent years it has been found that the type of rocks under where you live can magnify the effect a CME can have on things like the power grid by up to 100 times. Igneous and metamorphic rocks have a very high electrical resistance while sedimentary rocks which have water in them have a very low electrical resistance and allow electrical currents induced into them to flow.
Now whilst it might seem that a highly resistive rock like Igneous and metamorphic ones would be a good thing, they act like a giant insulator but the power lines that cross them provide a short circuit through their ground connection allowing currents to build up and flow through them to damage things like transformers. The North Eastern US was also badly hit by the 1989 storm and was on the verge of a shut down and again much of that area is covered by the Appalachian mountain range which is Igneous and metamorphic in its makeup.
In the United Kingdom, the highland area of Scotland is igneous and metamorphic rock where as the farther south east you go in England they are mostly sedimentary rocks, so Scotland could be affected much more than England.
In recently declassified US Navy documents, the crew of a US Task Force 77 aircraft saw a group of 20-25 magnetic sea mines which were laid by the US off the coast of Vietnam at Hai Phong, detonate over a 30 second period on August 4th 1972. At the time there was no obvious reason as to why this should have happened. The mines had a self destruct time built time but that was not for another 30 days or so.
However, the US Navy noticed that an X-class solar flare had been detected earlier that day and in a record 14.6 hours a CME hit the Earth. Although the DST value was only -125Nt, its thought that the speed at which it hit the Earths magnetosphere caused it to compress in a similar way to a larger storm and it was this rapid change in the earth’s magnetic field that triggered the magnetic mines.
By mapping the resistance of the rocks and the local magnetic hot spots in the US and other countries its possible to work out where large currents could build up and thus to make provisions in the power grid connectivity.
In the UK the National Grid has been replacing high voltage transformers with newer designs that are more resilient to extra current surges. The strategy in the UK is that if large CME is expected and the polarity is opposite to the earths, they will turn on as much of the 8000km of the UK power lines as possible to dump energy over the entire system and drain it back to earth rather than allowing it to overload a few key system areas and causing costly and lengthy repairs.
Places like the US, Canada and even Australia where there are very long high voltage cable runs which run north to south over varying geologies are more susceptible. Even with blocking capacitors installed, early warnings from satellite observations will be key to knowing which parts might be affected more than others and as such which to protect or temporarily shut down to avoid long term damage.
With our much-increased knowledge of how solar weather affects us here on earth and how the earth its self reacts, it much less likely that even a Carrington class event would have much impact on the countries like the UK which have prepared for this kind of situation but in the end, it’s down to the individual countries and their power companies to make sure that when that once in a hundred year CME comes along the lights won’t go out.