The electromagnetic signal due to the interaction of nuclear explosions with the Earth's magnetic field

There are two mechanisms by which the earth's magnetic field affects the electromagnetic signal from a nuclear explosion in the atmosphere. First, the Compton recoil electrons generated in the air by explosion γ rays interact with the earth's magnetic field producing a ‘back’ field that tends to cancel the earth's field in the region near the explosion. Such a cancellation is equivalent to radiation from a magnetic dipole. Approximate calculations described here indicate that this ‘back’ field is small at sea level, but increases with altitude. The other mechanism is that the earth's field is perturbed by the blast wave motion of heated (conducting) air. Calculations indicate that this mechanism produces a substantial effect, and its magnitude is crudely estimated.