Coupling of lightning generated electromagnetic waves to the inner magnetosphere: a case study

Our case study aims at contributing to the discussion on sources of plasmaspheric hiss, which is known for its interactions with the Earth radiation belts. We analyze multi-point measurements of electromagnetic field waves by the Wide Band Data instruments onboard the four Cluster spacecraft in order to find sources of hiss observed close to the geomagnetic equator in the dayside outer plasmasphere. We find hiss to be triggered from whistlers of different spectral properties. Whistlers with the lowest observed dispersion arrive to different spacecraft with time delays indicating their origin in the northern hemisphere. Positions of source lightning discharges are then found using the time coincidences with the Word Wide Lightning Location Network data from three active thunderstorm regions in Europe. We find that subionospheric propagation of lightning atmospherics is necessary to explain the observations. Geographic locations of their ionospheric exit points then determine spectral properties of resulting unducted whistlers and triggered hiss. By this well documented chain of events starting with a lightning discharge in the atmosphere we confirm that magnetospherically reflecting whistlers and hiss triggered from them are among possible sources of plasmaspheric hiss.