Balser and Wagner , using a vertical antenna, have recently measured the spectrum of natural noise in the frequency region 4–35 c/s. The results are shown in Figure 3. This note reports preliminary results of a theory advanced to account for the detailed shape of this spectrum.
Experimentally observed VLF noise is thought to consist of a superposition of responses from lightning flashes all over the world. Therefore, assuming that this hypothesis is correct down to ELF, a theoretical model based on it should yield more accurate calculations of the spectrum of observed ELF noise than a theory based on response to a single impulse source. Such a model has been constructed and used to calculate the ELF noise spectrum, and the results have been compared with the experimental results referred to above.