# Would a nuclear explosion over one of the Earth’s magnetic poles momentarily disrupt/weaken the Earth’s magnetic field?

If say the Tsar Bomba had been detonated directly over one of the Earth’s magnetic poles at ground level, would the nuclear electromagnetic pulse generated from that blast have had any momentary effect on the strength of Earth’s magnetic field?

If a nuclear EMP cannot disrupt/weaken the Earth’s magnetic field, would it still be powerful enough to momentarily energize the Earth magnetic field and would this powerful electromagnetic discharge fry any sensitive electronics devices around the Earth and/or satellites in low Earth orbit?

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• This is off-topic, also your idea is simply bad. Where Tsar Bomba detonated didn't have much difference as far as Earth is concerned. – Mithoron Aug 14 '18 at 22:02
• @Mithoron The EMP pulse of the nuclear blast is very short, the question ("...momentarily...") asks for the sudden effect. My first thought was what you said, but for the second I am not so sure. I think it worths a discussion, because an objective answer likely exists and it is ontopic. – peterh Aug 14 '18 at 23:34
• @peterh The answer is "No, no, no!" and I can't see anything on-topic. – Mithoron Aug 14 '18 at 23:44
• Since the Earth's magnetic field is generated deep inside the planet and a nuclear blast is at or very near the surface, I do not see how such a blast, regardless of how strong, could effect the Earth's magnetic field in any measurable, meaningful way. – BillDOe Aug 15 '18 at 18:19

“to momentarily energize the Earth magnetic field”... hm.

A nuclear explosion has two effects that one could connect with the subject of magnetic fields:

1. The EMP. This is very quick. Like any EM signal, it just follows the wave solution of the Maxwell equations (which are in air very linear, so the amplitude isn't really important), meaning it spreads out at the speed of light, well ahead of the pressure and ionisation effects. The lower-frequency parts will partly be reflected at the ionosphere, you may get some whistler-mode dispesion. This isn't really special to the nuclear bomb (it also happens with lightning transients), and it's completely independent of the Earth's static magnetic field. Yes, the EMP itself also has a magnetic component, but this is short-lived and actually not that strong; only because it's a dynamic field with a strong electrical component does the pulse destroy electronics. (Magnetically, it's much weaker that the disturbances solar flares can cause on Earth.)
2. The ionisation. A nuclear bomb turns a significant volume of air into plasma, both through the heating and through radiation. In plasma, you don't have separate dynamics for the gas and EM fields anymore, but both are linked together in magnetohydrodynamics. However, not much air is heated so much that, at the high densities you have a surface level, you'd actually have electrical conductivity for a long time – recombination removes most of the ions quickly. Only a high voltage would be able to sustain a current (and thus effect a magnetic field), which again is just what happens in a lightning, but that too is short-lived.

So, no, I don't think there's much interesting to be said here.

It might also be worth noting that the Tsar Bomba actually did explode at quite high latitude, 74°N. At that time the magnetic pole itself was only at 75°N (albeit on the western hemisphere, so the explosion wasn't actually at very high magnetic latitude).

The hard radiation which does most of the initial heating in the fireball does so precisely because it interacts strongly with air, but that also means it doesn't reach very far. The components that reach through air can immediately burn surfaces miles away, but they don't much heat the air they pass through. Only the mechanical (i.e. acoustic) shock wave causes a heating again, but this is transient.

• I think although the magnetic effect propagates with $c$, the important factor to determine its duration depends more on the active time length of the source. It might be much longer, maybe even tenths of seconds (my own estimation). – peterh Aug 16 '18 at 18:41
• @peterh I'm not really an expert on nuclear weapons, but the superficial research suggests that most of the EMP energy is in the “E1” pulse, which only lasts nanoseconds. Makes sense, because the violence of this pulse is due to relativistic effects, so it can only work as a quick transient. The slower E2 and E3 components aren't that strong. – leftaroundabout Aug 17 '18 at 10:25

There are a few different questions lurking here.

• No, it would not have any lasting effect on the Earth's magnetic field. That field is not generated at the surface, at the poles or otherwise.

• Yes, it would produce an electromagnetic pulse, and that could be harmful to unshielded electronics in at least a line-of-sight sense.

• Yes, this EMP would definitely cause localized magnetic effects for a very brief moment, which one could argue constitute a change in the natural magnetic field.

• I'm not sure whether there's any reason to think that the earth's magnetic field could help these effects to propagate beyond line of sight - which I think is what you're really asking. Perhaps a physicist could chime in...

• @Semifiurnal Simon, since a magnetic field is essentially a continuous flow of photons, I think that an obstacle put in the path of those photons would an effect on the magnetic field. A nuclear explosion produces gamma rays and x-rays which may interact with the flow of the photons moving between the North and South magnetic poles. – user13650 Aug 16 '18 at 13:37
• Also, a nuclear EMP will produce electrical energy and this concentrated electrical energy produced over a magnetic pole may be dissipated throughout the Earth’s magnetic field causing damage to sensitive electronics. – user13650 Aug 16 '18 at 13:48
• Query regarding the second point. Did you mean harmful to shielded or unshielded electronics? – Fred Aug 16 '18 at 14:20
• @Fred, to unshielded electronics – user13650 Aug 16 '18 at 15:02
• @FanofComets " since a magnetic field is essentially a continuous flow of photons" - I think you need to consult a physicist. – Semidiurnal Simon Aug 16 '18 at 19:39