Multiple roles of plasma waves in Geospace

There are several plasma and particle populations in the Geospace. The plasmasphere consists of cold/dense plasma populations, and the ionosphere is the source of the plasmaspheric plasma. The ring current and plasma sheet energies range from a few keV to about 100 keV, and these populations contribute to the ambient plasma pressure. The energies of the radiation belt particles range from a few hundred keV to more than 10 MeV, which are the highest energy population in geospace. Thus, plasma and particle populations with a wide range of energies from a few eV to more than 10 MeV coexist in the inner magnetosphere. Besides plasma/particle populations, there are different kinds of plasma waves at the wide frequency range from ULF to HF frequency range in geospace. Geospace is often referred as "zoo of plasma waves", i.e., there exist MHD waves in the low-frequency range, ion cyclotron waves, whistler mode waves, free space mode waves, and several kinds of electrostatic waves. These waves work essential roles for dynamical evolutions of plasma/particles in geospace via the cross-energy coupling. The geospace exploration satellite Arase (ERG) has been launched in 2016 and started the prime mission from the end of March 2017 [ Miyoshi et al., 2018 ]. The Arase satellite observes 3-dimenational distribution function and/or pitch angle distribution for wide energy electrons (~20 eV – a few MeV) and ions (10 eV/q – 180 keV/q with mass discriminations. The satellite also measures electric fields from DC to 10 MHz with three different receivers and magnetic fields from DC to 100 kHz with fluxgate and search coil magnetometer [ Kasahara et al., 2018 , Matsuda et al., 2018 , Matsuoka et al., 2018 ]. As an example, heating and acceleration of plasma and energetic electrons and ions are identified by Arase. Arase also observed direct evidence to show scattering of energetic electrons by whistler mode waves, which cause the aurora emissions in the ionosphere. In this presentation, we will show some highlight observations from Arase and discuss future directions of measurement of plasma waves in geospace.