[mikeash]

EMP from nuclear detonations is more of a high altitude thing. The gamma rays knock electrons off atoms in the atmosphere, which move really fast because the gamma rays are energetic. Up where the atmosphere is thin, those electrons can move a substantial distance before the collide with another atom. As they move, the Earth's magnetic field causes their path to curve, which causes them to emit electromagnetic radiation. At lower altitudes (which a bomber interception would be, relatively speaking) the electrons don't get far enough before they collide with stuff.