Natural atmospheric noise statistics from VLF measurements in the eastern Mediterranean

Very low frequency (VLF) (3-30 kHz) and extremely low frequency (ELF) (3-3000 Hz) electromagnetic transient signals and noise are generated by various natural and anthropogenic processes. On a global basis by far the most significant source is ELF/VLF radiation from lightning propagating in the Earth-ionosphere waveguide. This atmospheric "noise," originating essentially from lightning discharges, is the main source of interference for VLF/LF telecommunications. One of the statistical measures that is used to define the properties of low-frequency radio noise is the voltage deviation V_d, which is a measure of the impulsiveness of the noise that is widely used to characterize radio noise, particularly in the International Radio Consultative Committee reports. In this paper we present atmospheric noise statistics based on VLF measurements at different temporal resolution (from minutes to seasonal variations). For the first time we present analysis of the statistical parameters of V_d from continuous broadband VLF measurements for a period extending more than 1 year. Our analysis shows that the long-term observed V_d characteristics can be reasonably estimated as the sum of two Gaussians distribution functions, while the hourly and seasonal distributions of V_d values can be fitted using a single Gaussian distribution with different mean and variance values.