On the Peculiar Properties of Extremely Low Frequency Lightning Generated Whistlers Detected at Low Earth Orbit Altitudes Close to the Magnetic Equator

Abstract Lightning strikes generate broadband electromagnetic signals. At Extremely Low Frequencies (ELF), these signals partly leak into the ionosphere and produce so‐called Lightning Generated (LG) whistlers that the Absolute Scalar Magnetometers on board the ESA Swarm satellites can detect. The dispersion of LG whistlers has been empirically described by Eckersley (1935, https://doi.org/10.1038/135104a0 ): , where is the group delay of a wave packet, its frequency and is called the dispersion of the whistler. Although we find that ELF LG whistlers detected by Swarm generally follow this law, this is not the case for those detected close to the magnetic equator. Modeling ELF LG whistlers with ray‐tracing technique successfully predicts the observed dispersions and allows us to decipher what makes ELF LG equatorial whistlers different. For such whistlers, low frequencies follow rays with shorter paths than high frequencies, partly compensating for the fact that high frequencies travel faster.