Cloud Lightning: Detection and Utilization for Total Lightning Measured in the VLF/LF Regime

Abstract

Lightning detection networks operating in the VLF/LF-regime have been traditionally designed to report cloud-to-ground (CG) strokes with currents above ~5 kA while they suppress recording of all types of cloud discharges (IC) by special methods. Efficient detection and reporting of IC emission has been achieved mainly with VHF arrays. The Munich group studies VLF/LF radiation with methods equally sensitive to CG and IC signals and utilized a new 21-sensor network (LINET, lightning detection network) to obtain total lightning data by means of a single technique. Three important network features are i) the measurement of estimated currents as low as ~1 kA, a range which has attracted little experimental attention in the past, ii) discrimination of IC events from CG strokes by means of a special 3D-feature in the location algorithm, and (iii) the reporting of IC emission heights. In accordance with general expectations, high IC event rates have been found at low amplitudes. Typical IC’s exhibit multi-polar pulse-trains which defy assignment of a clear-cut sign for the amplitude; however, there is also a large portion of IC events which are sufficiently mono-polar to allow classification as having positive or negative polarity. In most storm cells an excess of positive polarity IC (IC+) events is found; together with negative polarity IC (IC-) events promising information is obtained about discharge types, identification of storm cells and of the onset of super-cell storms and severe weather conditions.