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An Application of Transfer Entropy to Analyzing Cross-Scale Coupling Processes in MHD Simulations of Kelvin-Helmholtz Instabilities
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Detecting Cross-Scale Coupling in MHD Simulations of Kelvin-Helmholtz Instabilities with Transfer Entropy
No full textThe roles of flux-tube entropy and effective gravity in the inward plasma transport at Saturn
No full textObservation and numerical simulation of cold ions energized by EMIC waves
No full textThis is the first report of significant energization (up to 7,000 eV) of low-energy He+ ions, which occurred simultaneously with H-band electromagnetic ion cyclotron (EMIC) wave activity, in a direction mostly perpendicular to the ambient magnetic field. The event was detected by the Arase satellite in the dayside plasmatrough region off the magnetic equator on 15 May 2019. The peak energy of the He+ flux enhancements is mostly above 1,000 eV. At some interval, the He+ ions are energized up to ∼7,000 eV. The H-band waves are excited in a frequency band between the local crossover and helium gyrofrequencies and are close to a linear polarization state with weakly left-handed or right-handed polarization. The normal angle of the waves exhibits significant variation between 0° and 80°, indicating a non-parallel propagation. We run a hybrid code with parameters estimated from the Arase observations to examine the He+ energization. The simulations show that cold He+ ions are energized up to more than 1,000 eV, similar to the spacecraft observations. From the analysis of the simulated wave fields and cold plasma motions, we found that the ratio of the wave frequency to He+ gyrofrequency is a primary factor for transverse energization of cold He+ ions. As a consequence of the numerical analysis, we suggest that the significant transverse energization of He+ ions observed by Arase is attributed to H-band EMIC waves excited near the local helium gyrofrequency
O-mode instability for non-thermal continuum radiation generated near the plasmapause
No full textAnalysis of the ordinary mode (O-mode) instability is performed to comprehend the nonthermal continuum (NTC) radiation near the plasmapause, taking into account the relativistic wave-electron resonance effect. The energy source is the anisotropy in the velocity of the minority suprathermal electron population. Numerical solutions demonstrate that the O-mode can be unstable with multiple narrow frequency bands located close to harmonics of the electron cyclotron frequency above the local electron plasma frequency. These waves have narrow beaming angle bands of nearly 90º relative to the ambient magnetic field. Our findings indicate that NTC radiation generated by this wave-electron resonance instability near the plasmapause can propagate nearer to the magnetic equator with multiple harmonics, which is in agreement with a recent statistical study using Van Allen Probes
