[thedoc (OP)]

Ed Wilson  asked the Naked Scientists:
   
Accepting its limitations I've used Wikipedia information as the basis of my back-of-an-envelope calculations. Please point out any errors in assumptions, logic or arithmetic.

The estimate is that a Carrington event has a 12% chance of occurring between 2012 and 2022.  I'm assuming that's based on known cycles of solar activity.

But a Carrington event is not just a coronal mass ejection (CME).  It's a CME which hits the earth (or its magnetic field).  

My calculations make the area of a section through the earth = 127516118 square kilometres
and the surface area of a sphere of radius (distance from sun to earth) = 282743trillion square kilometres

The area of intersection of those two is about 1/20million the area of the big sphere, so you'd think the chance of any particular CME  hitting us would be slight.  I know they're big beasts and one might only have to clip the magnetic field, but even so...

1.  Are CMEs extremely frequent?
2.  Are they emitted preferentially in the orbital plane of the planets?
3.  Have I got this horribly wrong?

I could probably work it all out for myself if I read further, but my brain's beginning to hurt, so I wondered if you could help.

What do you think?

[CliffordK]

Those numbers seem a bit high.

According to Wikipedia, a a Carrington sized solar event may impact Earth about once every 500 years.  Each event is likely independent, so with simple math, over the next decade, it would be about a 1:50 chance, or about 2%. 

There are, of course, smaller events such as the one that struck Canada in 1989 which could still wreak havoc on our electronic infrastructure.

Our current solar cycle is one of the weakest in a century, and some very early estimates (and perhaps more wishful thinking than accurate) indicate the next cycle may be even weaker.  Of course Solar Cycle 10 in 1859 wasn't particularly strong, and estimates are that at least one flare that missed Earth in 2012 could have been of similar strength to the Carrington flare.  But the weaker cycles should reduce the probability somewhat.

The impact of a CME would be generally a cone traveling from the surface of the sun out into space.  I'm not sure how many degrees, but don't consider a laser pointer directed towards Earth.  Small CME's frequently occur on the sun's surface, perhaps on a weekly basis.  Large ones are somewhat less frequent.  However, we haven't had the ability to fully track them until recently. 

Sun spots aren't always in the plane of the planets.  If you look at what is often called a "butterfly chart", you will see that most of the sunspots early in each solar cycle are in the polar regions of the sun, and thus would have less of a chance of impacting Earth.  Starting at about the solar maximum (where we are now), some of the sunspots start occurring near the sun's equator, and thus having CMEs in the plane of the planets.

Anyway, looking at potential large CME's impacting Earth, the highest liklihood in the next decade would be either in the next couple of years (say before 2017) near the current solar maximum, or in the middle of the next solar cycle, say after about 2022, with a low probability period late in this decade and early next decade.

[alancalverd]

The key word here is "catastrophic".

Our neolithic ancestors were happy if the sun rose regularly, and whilst snow made home life temporarily uncomfortable, it made hunting a lot easier. Thus anything short of a year-long eclipse would not have been considered catastrophic.

Modern society is increasingly interdependent, fragile, and intolerant of failure. Temporary loss of the electricity grid, which has only existed for less than a century, has shut down large chunks of North America for days, with enough attributable death and destruction to be considered a disaster if not a catastrophe. As more and more coal- and oil-burning machinery is replaced by "clean" electrical equipment, we can anticipate cities being wiped out in a couple of weeks by disease from a lack of water and sewage.

Disruption of long-range radio communication would ground all scheduled flights. This might appear as a temporary inconvenience but containing half a million displaced persons (the number of air passengers passing through London's airports in one day) for more than a week (food and drink would run out in one day, no trains, and the road exits blocked as soon as the traffic lights fail....) would stretch the resources of an army that, frankly, has more important things to do.

Hospital patients would begin to die by about Day 3 of a major power cut, as nobody has "essential diesel power" reserves for more than 2 days. Lack of communication would prevent proper disposal of the bodies.

And so it goes on. The point is that what might have been a small event a century ago, would be a catastrophe today, as evidenced by the effect of hurricanes and tsunamis on increasingly dense and fragile coastal conurbations.

If anyone feels like writing the screenplay for the next big disaster movie ("Carrington" is a catchy title), do please get in touch. There's no doubt about the underlying engineering, but shall we let Bruce Willis and Jodie Foster save the planet, or make an art film where everyone dies?

[dlorde]

One major problem with such an event would be the difficulty of recovering a viable industry to make new infrastructure. Modern large-scale manufacturing requires large-scale electricity distribution, which requires an electrical grid. Even if you could get the power stations functioning again, key components of electrical grids are transformers, which would be destroyed. I'm told that there is no significant stockpile of grid transformers, and manufacturing them is a slow process requiring parts from many industries that also rely on electricity... A few generators here and there won't be enough, and manufacturing more generators also requires electricity.

I had thought that a partial solution would be to decouple as many transformers as possible prior to the arrival of such a solar event, so they don't get blown, but apparently (at least in the UK) policy is to connect the whole grid so as to dissipate the generated current as much as possible and avoid overloading any particular part. This would mean an extreme event would potentially destroy the whole grid rather than just part of it. Perhaps the strategy would change for a known Carrington-scale event, I don't know.

[alancalverd]

I'm told that there is no significant stockpile of grid transformers, and manufacturing them is a slow process requiring parts from many industries that also rely on electricity... A few generators here and there won't be enough, and manufacturing more generators also requires electricity.

Something of an understatement. Current lead time one more than two 11 kV/400 kVA units is about 6 weeks in any one region of the country, and quite how you order them if the telephone system is down, I have no idea. Getting hold of a 400 kV multimegawatt unit is another story altogether.

[CliffordK]

Fortunately the speed of light is much faster than the speed of the solar wind.  So presumably one could have a 24 hour notice prior to a large CME event impacting Earth. 

We have Tsunami early warning systems.  Perhaps one should design a CME early warning system. 

Of course, that will probably only come after a CME that throws us back in to the Dark Ages. 

Shutting down and disconnecting much of the grid would help, but it may be an extremely labor intensive process. 

Some equipment such as Nuke Plants may take more than 24 hours to shut down, even if the decision to shut them down comes immediately after an impending CME is detected.

Keep in mind it is not just the transformers that would blow, but anything actually connected to the grid would be at risk.  I've had power supplies in equipment blow when transformers blow, or otherwise there is a major power surge. 

A strong enough EMP may even affect instruments that are otherwise powered down.  And, how much of our world is not really powered off when shut down?

Ohhhh.... 
According to Wikipedia, CME's have been detected up to about 3,200 km/s which puts one down to about 12 hours early warning for a powerful one.   And, if it happens in the middle of the night (at least somewhere on Earth), one could potentially tune-out at 8:00 PM, and be slammed at 8:00 AM.