EMP pulse

EMP stands for Electromagnetic Pulse is is the result of a nuclear explosion.
If the bomb is not focused to specific forms of energy or radiation, i.e
neutron bombs, then energy is released all across the
spectrum from microwaves, light, heat, x-rays, gamma rays etc.  An EMP
does damage by overloading the system with a huge pulse of energy across

the whole bandwidth. One example of intense microwave radiation would be
putting a metal object in your kitchen microwave. Multiply the light show from
your 200 watt microwave to the megawatts generated by EMP and you can see how
electronics get fried. The only reason a nuke would be set off in the
atmosphere and not higher up in orbit is that a lot of the powerful radiation
(i.e. short wavelengths) tends to disperse quickly unless focused and since
it's difficult to point a nuclear blast, to get

the most out of a bomb it needs to be relatively close to the target, about
200 miles up to get good coverage of 80% of the lower 48 and some of Alaska.

--Binhan