Relation between fine structure of energy spectra for pulsating aurora electrons and frequency spectra of whistler mode chorus waves
Abstract
We investigate the origin of the fine structure of the energy spectrum of precipitating electrons for the pulsating aurora (PsA) observed by the low-altitude Reimei satellite. The Reimei satellite achieved simultaneous observations of the optical images and precipitating electrons of the PsA from satellite altitude (similar to 620km) with resolution of 40ms.
The main modulation of precipitation, with a few seconds, and the internal modulations, with a few hertz, that are embedded inside the main modulations are identified above similar to 3keV. Moreover, stable precipitations at similar to 1keV are found for the PsA.
A precipitation gap is discovered between two energy bands. We identify the origin of the fine structure of the energy spectrum for the precipitating electrons using the computer simulation on the wave-particle interaction between electrons and chorus waves.
The lower band chorus (LBC) bursts cause the main modulation of energetic electrons, and the generation and collapse of the LBC bursts determines on-off switching of the PsA. A train of rising tone elements embedded in the LBC bursts drives the internal modulations.
A close set of upper band chorus (UBC) waves causes the stable precipitations at similar to 1keV. We show that a wave power gap around the half gyrofrequency at the equatorial plane in the magnetosphere between LBC and UBC reduces the loss rate of electrons at the intermediate energy range, forming a gap of precipitating electrons in the ionosphere.