People are talking about what, to me, seem like a cartoonish version of the threat posed by an EMP attack on the US. The story goes something like this: a rogue state like N. Korea decides it is tired of the US and its meddling, and launches an EMP attack. Using just one single nuclear weapon to produce a powerful EMP, all electronics in the nation are fried in one stroke. Everything stops working, chaos in the streets, I hope you stockpiled ammo in advance.
It doesn’t seem to add up. I don’t doubt that there is such a thing as an EMP generated by a nuclear weapon, but IIRC the intensity of that declines the farther you get from the source at the rate of 1/r^2. It seems like the effect should be pretty local, not orders of magnitude larger than the blast radius.
But- I don’t know the magnitude of charge generated by nukes and I can’t estimate the effective range of an EMP. Am I on the right track here, or is it actually me who is… in the dark?
I think you should read “Arsenal,” by Kosta Tsipis, (1983). In chapter 3, (page 60) he details the effects of an EMP burst. It’s frightening. A thermonuclear burst high above the middle United States would effectively eliminate radio communications nationwide, as well as destroy most of our modern [computer] electronics devices within 1000 miles of the airburst.
An airburst EMP is a real thing, and a real threat…to any nation.
An exoatmospheric nuclear explosion a high altitute electromagnetic pulse (HEMP) which can cover a large region by the interaction of X-rays with the ionosphere, producing a semi-coherent pulse that would energize any delicate electronics attached to some kind of external antenna or input. At the 50 kv/m atmospheric breakdown threshold, it could be expected to damage commercial electronics across a regional and perhaps national range. This is not a direct effect of radiation from the device but rather overcharging of ionized particles, hence the much longer range than 1/r[SUP]2[/SUP], and the actualy field of effect depends upon the altitude at which it was detonated and intensity of X-ray radiation that is produced.
Whether North Korea could effect such an attack is another question as it requires a high radiation yield at a specific altitude, but for technically competent attacker it would be entirely plausible to both disable consumer electronics across a wide region as well as do substantial damage to the North American electrical distribution grid.
An EMP attack on the electrical grid will succeed or fail for many reasons.
The grid is a complex system. But it has safeguards built in. It also has weaknesses that have caused large blackouts from smaller incidents snowballing in effect.
Any force that radiates from a point is victim to the inverse square law. The further away from the source, the less energy per area. So the effects of EMP fall off rapidly with distance. But the grid is a complex combination of antennas to absorb that energy and ground points to dissipate it. Devices attached to the grid have their own more or less vulnerable characteristics as well.
I don’t think any accurate estimate of damage is possible. Nor how long it would take to repair it. The variables are too many.
Solar events worry me more. They can impact the entire continent with equal and large power at almost every point at the same time. Also destroying satellites.
This is the thing right here. The effects drop quickly with distance.
I used to do IT stuff in hospitals and we occasionally had to install a PC near an MRI. The permanent magnet in those things were huge! We were given drawings of the field strength and had to make sure all the electronic equipment we installed was outside a certain range.
I was kind of amazed at how close we could be (maybe 10-15 feet) and all was ok. It dropped rapidly too. Under 10 feet might demagnetize your credit cards. 11+ feet and no problem.
That said modern electronics work on very low currents. An EMP induced current can fry modern electronics with ease because it takes so little to surpass their tolerances.
Magnetic fields fall off even more quickly than 1/r^2. That’s what you would get from a magnetic monopole, but those are really rare (there are expected to be approximately zero in the known Universe). For any magnet you’ll actually encounter, it’ll be at least a dipole, which falls off as 1/r^3.
Chronos: It is hard to think of a nuclear blast as a dipole as it emanates from what might as well be a point source. But what do I know about the electromechanics of nukes? Not much. Maybe you could say a little more about what is going on in a blast to produce this effect?
Stranger: We should hang out sometime. You’re saying it isn’t the EMP from the blast at all, but rather a sort of electromagnetic hijacking of the upper atmosphere that causes this effect. So what, the ionosphere becomes highly charged and basically grounds itself like a 1000 mile radius stroke of lightning, frying electronics everywhere? Can you say a little more about the interaction of x-rays with the atmosphere, how they are generated by the blast, and why it could extend over such a large area?
Thanks to everybody else too. I do know people in RL who can answer questions like this, but their patience is limited
EMP is caused when x-rays from the explosion ionize the rarified atmosphere. The free electrons created then follow the Earth’s magnetic field and travel downwards. These free electrons create a large potential gradient, which induces large voltages in any long wires.
In a vacuum, a large part of a nuclear explosion’s energy is released as X-rays. There is no blast in space. In fact, the blast is caused by the absorption of x-rays with the atmosphere. So, in space, the x-rays from the explosion will travel outwards from the explosion until they reach the atmosphere, or just get lost in space.
