Very Low Frequency Whistler Mode Wave Events Observed Simultaneously by the Kannuslehto Station and Van Allen Probes

Abstract

Abstract

Events characterized by substantial intensity enhancements in the frequency range between about 1.5 and 4 kHz in the measurements of the ground-based Kannuslehto station, Finland are analyzed. Altogether, as many as 465 events are identified in the Kannuslehto data measured during the campaigns between December 2012 and October 2019. It is shown that the events usually last for several hours and they occur preferentially on the dawn side during geomagnetically active periods. Simultaneous measurements performed by the Van Allen Probes spacecraft are used to reveal the L-shells and magnetic local times where a corresponding intensity increase occurs in space. A backward ray tracing analysis is further employed to investigate the wave propagation between the tentative source region and the ground. Wave normal angles of waves eventually detectable at Kannuslehto are determined and compared with those obtained from a detailed wave analysis. Either a wave ducting, propagation in the Earth-ionosphere waveguide, or their combination seem to be needed for the waves to reach Kannuslehto.