Study of Spatiotemporal Development of Global Distribution of Magnetospheric ELF/VLF Waves Using Ground‐Based and Satellite Observations, and RAM‐SCB Simulations, for the March and November 2017 Storms

Abstract

Magnetospheric Extremely Low‐Frequency/Very Low‐Frequency (ELF/VLF) waves have an important role in the acceleration and loss of energetic electrons in the magnetosphere through wave‐particle interaction. It is necessary to understand the spatiotemporal development of magnetospheric ELF/VLF waves to quantitatively estimate this effect of wave‐particle interaction, a global process not yet well understood. We investigated spatiotemporal development of magnetospheric ELF/VLF waves using 6 PWING ground‐based stations at subauroral latitudes, Exploration of energization and Radiation in Geospace and RBSP satellites, POES/MetOp satellites, and the RAM‐SCB model, focusing on the March and November 2017 storms driven by corotating interaction regions in the solar wind. Our results show that the ELF/VLF waves are enhanced over a longitudinal extent from midnight to morning and dayside associated with substorm electron injections. In the main to early storm recovery phase, we observe continuous ELF/VLF waves from ∼0 to ∼12 MLT in the dawn sector. This wide extent seems to be caused by frequent occurrence of substorms. The wave region expands eastward in association with the drift of source electrons injected by substorms from the nightside. We also observed dayside ELF/VLF wave enhancement, possibly driven by magnetospheric compression by solar wind, over an MLT extent of at least 5 h. Ground observations tend not to observe ELF/VLF waves in the post‐midnight sector, although other methods clearly show the existence of waves. This is possibly due to Landau damping of the waves, the absence of the plasma density duct structure, and/or enhanced auroral ionization of the ionosphere in the post‐midnight sector.

Relative Contribution of ULF Waves and Whistler‐Mode Chorus to the Radiation Belt Variation During the May 2017 Storm

“…Note that the quantitative analysis regarding the global picture of wave contribution is not addressed in this study because it is difficult to derive the spatial distribution of waves only from in‐situ observations. For example, the wave estimation technique based on the distributions of observed precipitating hot electrons detected by NOAA POES satellites (e.g., Chen et al., 2014; Takeshita et al., 2021) would be helpful for the quantitative discussion of the wave contribution. The different time sequences of wave contributions are sometimes observed during other magnetic storms.…”

Possible Global Generation Region of Nonlinear Whistler‐Mode Chorus Emission Waves at Mercury

“…They also showed that the spatial chorus development is mostly suppressed in the linear growth in the slow solar wind case, but it can still take place the nonlinear growth as exciting dawn chorus in the premidnight-postdawn region in relatively weak geomagnetic activities. Moreover, Takeshita et al (2021) showed a global spatiotemporal development (a longitudinal extent from midnight to morning and dayside associated with substorm electron injections) of the Earth's whistler mode waves given from the linear growth rate using the temperature anisotropy, hot electron density, ambient magnetic field, and cold density by a global simulation. The possible spatial development of chorus generation can be quantitatively estimated by the hot and cold electron densities and ambient magnetic fields (intensity and curvature) from these previous studies based on the linear and nonlinear wave growths.…”