electromagnetic pulse

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The pulse of intense electromagnetic radiation generated by a nuclear explosion.
• noun A short-duration, broadband, high-intensity emission of electromagnetic energy, such as lightning.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A short-duration burst of high-intensity electromagnetic radiation generated by a physical event, in particular by a large thermonuclear explosion in the atmosphere. The pulse causes a damaging surge of voltage within electrical and electronic systems.
• noun Compton-recoil electrons and photoelectrons from photons scattered in the materials of a nuclear event causing electric and magnetic fields to couple with electrical and electronic systems to produce damaging current surges.