Electromagnetic ion cyclotron (EMIC) waves potentially cause precipitation loss of relativistic electrons from the outer radiation belt to the atmosphere through pitch angle scattering. However, the direct evidence of each EMIC wave element and burst of precipitation has not yet been reported. Here we show the temporal and spatial correspondence of the EMIC waves with relativistic electron precipitation (REP) during the geomagnetic storm of 27 March 2017. EMIC waves were observed at several stations in North America. REP was detected as a decrease of subionospheric radio amplitudes observed at Athabasca, Canada. When isolated proton aurora, observed at Athabasca, appeared on the radio propagation path, we found a good correspondence between the temporal variations of REP and EMIC waves, and REP preceded EMIC waves by 24 s. This time lag is consistent with the travel time difference between relativistic electrons and EMIC waves from the magnetospheric equatorial plane to the ionosphere.
- EMIC waves
- energetic electron precipitation
- subionosheric propagation