Study of Positive Lightning Discharges in WWLLN Data Using Extremely Low Frequency Electromagnetic Wave Measurements

An automatic procedure for identification of VLF detected lightning discharges in Extremely Low Frequency (ELF) measurements is presented to enable large scale analysis of global lightning and ELF propagation properties which are determined by the lower ionosphere. Using a single ELF sensor in Poland we are able to identify the majority (∼80% or more) of lightning events detected by the WWLLN VLF network. Measured in ELF magnetic impulse components, EW and NS, enable the polarity (positive or negative) determination of the WWLLN‐detected strokes, thereby complementing the WWLLN data set with polarity information. We separately analyzed the data from Africa and from the whole globe, identifying positive discharges among all identified impulses. We find that the lightning energy evaluations based on VLF measurements are only weakly correlated with lightning charge moments, which manifest themselves in the measured signal amplitudes in the ELF band. The ratio of positive discharges shows an expected significant increase for the highest amplitude impulses. We also reveal a low amplitude component dominated by positive discharges that we attribute to artifacts of the recording hardware and filtering processes.