An assessment of whistlers generated from tree-like gigantic jets

Abstract

The characteristics of whistlers generated from an observed gigantic jet (GJ) are assessed and possible locations to detect these waves are deduced. Modeling is based on disturbances in the electric field, as measured by NCKU ELF/VLF station, associated with a tree-like GJ event over typhoon Lionrock. The power spectrum of GJ differs from that of common cloud-to-ground lightning; therefore, this study also investigates differences between GJ-generated signals and common lightning-generated whistlers. Detectability is evaluated by considering the absorption of amplitudes resulted from collisional damping associated with the propagation of generated waves. Our results show that in the ionosphere the waves are subject to greater attenuation as the frequency increases; however, a reversal occurs at lower frequencies of a few hundred Hz. The calculated waveforms show that the whistlers generated by the tree-like GJs are preceded by small fluctuations at high frequencies generated by the initiating lightning. Overall, the amplitudes increase with the passage of time; however, they are more randomly-distributed over time for whistlers generated from common lightning. The amplitudes decrease again when lower-frequency components below a few hundred Hz arrive. The amplitudes drop to the order of 1 mV/m as the waves propagate in the ionosphere, which puts them within a range detectable by the instruments on most satellites. Based on the locations of tree-like GJ events observed by ISUAL (Imager of Sprites and Upper Atmospheric Lightning), regions of the western and southeastern Pacific Ocean, as well as northern Africa region are the most likely locations to detect these whistlers.