The transient electrical activity of thunderstorms (primarily return and intracloud activity) generates electromagnetic (EM) radiation events known as sferics. A typical return stroke produces radiation peaking at ~10 kHz while typical intracloud stroke produces radiation peaking at a slightly higher frequency (at ~40 kHz) with 2 orders of magnitude less energy than a typical return stroke [Volland, 1995]. EM radiation at these frequencies propagates through the earth-ionosphere waveguide, so can be observed at large distances (greater than 2000 km) from the source.