Pitch angle distribution of relativistic electrons in the inner radiation belt and its relation to equatorial plasma wave turbulence phenomena

The pitch angle distribution of relativistic electrons in the inner radiation belt and its relation to local plasma waves were investigated using the data from the Akebono satellite. It was found that energetic electrons (> 1 MeV) in the inner radiation belt showed an unexpected dumbbell distribution near the magnetic equator. This feature was commonly observed both in magnetically disturbed and undisturbed conditions. It was also found that this anomalous pitch angle distribution of energetic electrons was always accompanied with the enhancement of local UHR waves around the magnetic equator. These newly found features indicate the existence of an unknown wave-particle interaction process between the relativistic electrons and quasi-electrostatic plasma waves in the equatorial region of the plasmaphere.