Measurement of sensitive current and charge motion using coherent averaging of remote low frequency magnetic field observations
Measuring lightning charge transfer, especially on time scales longer than several milliseconds, is a challenge. Instrumented towers can measure this quantity precisely but only for a tiny fraction of cloud-to-ground lightning. Electrostatic field measurements of lightning signals can provide robust estimates of this quantity, but the fast decay with distance of the electric field limits the measurement range to roughly 100 km at best. In contrast, low frequency and nearly-static magnetic fields from slowly varying lightning current decay much more slowly with distance and can therefore be measured at very long ranges. By measuring these low frequency magnetic fields, it is possible to broaden the geographic reach of lightning charge measurements. Sensitivity and noise, however, often limit these measurements to very large charge transfer lightning.
