Inner belt and slot region electron lifetimes and energization rates based on AKEBONO statistics of whistler waves

Abstract

Global statistics of the amplitude distributions of hiss, lightning‐generated, and other whistler mode waves from terrestrial VLF transmitters have been obtained from the EXOS‐D (Akebono) satellite in the Earth's plasmasphere and fitted as functions of L and latitude for two geomagnetic activity ranges (Kp<3 and Kp>3). In particular, the present study focuses on the inner zone L∈[1.4,2] where reliable in situ measurements were lacking. Such statistics are critically needed for an accurate assessment of the role and relative dominance of each type of wave in the dynamics of the inner radiation belt. While VLF waves seem to propagate mainly in a ducted mode at L∼1.5–3 for Kp<3, they appear to be substantially unducted during more disturbed periods (Kp>3). Hiss waves are generally the most intense in the inner belt, and lightning‐generated and hiss wave intensities increase with geomagnetic activity. Lightning‐generated wave amplitudes generally peak within 10° of the equator in the region L<2 where magnetosonic wave amplitudes are weak for Kp<3. Based on this statistics, simplified models of each wave type are presented. Quasi‐linear pitch angle and energy diffusion rates of electrons by the full wave model are then calculated. Corresponding electron lifetimes compare well with decay rates of trapped energetic electrons obtained from Solar Anomalous and Magnetospheric Particle Explorer and other satellites at L∈[1.4,2].