Simultaneous macroscale and microscale wave–ion interaction in near-earth space plasmas

Abstract

Identifying how energy transfer proceeds from macroscales down to microscales in collisionless plasmas is at the forefront of astrophysics and space physics. It provides information on the evolution of involved plasma systems and the generation of high-energy particles in the universe. Here we report two cross-scale energy-transfer events observed by NASA’s Magnetospheric Multiscale spacecraft in Earth’s magnetosphere. In these events, hot ions simultaneously undergo interactions with macroscale (~$${10}^{5}$$ 10 5 km) ultra-low-frequency waves and microscale ($$\sim {10}^{3}$$ ~ 10 3 km) electromagnetic-ion-cyclotron (EMIC) waves. The cross-scale interactions cause energy to directly transfer from macroscales to microscales, and finally dissipate at microscales via EMIC-wave-induced ion energization. The direct measurements of the energy transfer rate in the second event confirm the efficiency of this cross-scale transfer process, whose timescale is estimated to be roughly ten EMIC-wave periods about (1 min). Therefore, these observations experimentally demonstrate that simultaneous macroscale and microscale wave-ion interactions provide an efficient mechanism for cross-scale energy transfer and plasma energization in astrophysical and space plasmas.

Anomalous resonance between low-energy particles and electromagnetic plasma waves

“…which can also be expressed as Eq. (8). Similar conclusions can be also obtained via the modified Hamiltonian analysis 35,36 .…”

“…(1). These phase-bunching features are unambiguous manifestation of wave-particle cyclotron resonance 8,24 . More recently, spacecraft observations have also identified the formation of proton hills in phase space, which has been attributed to cyclotron resonance and believed to cause the frequency chirping of the observed EMIC waves 25 .…”

“…Cyclotron resonance plays a key, if not dominant role in shaping the particle dynamics in the near-Earth and planetary space environments. Two branches of plasma waves, namely, the electromagnetic ion cyclotron (EMIC) waves at frequencies slightly below the ion gyrofrequency 2,3 and the whistler-mode chorus waves below the electron gyrofrequency 4,5 , are especially important in accelerating positively-charged ions [6][7][8] and energetic electrons [9][10][11] , respectively. The latter process is also a major mechanism responsible for the formation of Earth's and Jupiter's radiation belts [12][13][14] .…”

Particle-sounding of the spatial structure of kinetic Alfvén waves

“…These stripes have a negative slope on the spectrogram and repeat at about 1-second intervals, following the frequency of the KAWs. Similar distributions have been reported in recent observations of cyclotron wave-ion interactions and explained as nonlinear gyrophase bunching of ions by wave perpendicular electric fields [37][38][39] . Phase-bunching stripes (PBSs) are also observed in higher energy channels (Figs.…”

Velocity-space Signatures of Resonant Energy Transfer between Whistler Waves and Electrons in the Earth’s Magnetosheath

“…Resonant wave-particle interactions include Landauresonant and cyclotron-resonant processes. They are efficient mechanisms to convert energy between electromagnetic fields and particles, causing particle acceleration/deceleration, the kinetic evolution of the particle velocity distribution function (VDF), and turbulence dissipation (Marsch et al 1982;Gurnett & Reinleitner 1983;He et al 2015;Xiao et al 2015;Chen et al 2019;Liu et al 2022). Nonresonant wave-particle interactions include stochastic heating and magnetic reconnection in wave fields (Johnson & Cheng 2001;Voitenko & Goossens 2004;Chandran et al 2010;Loureiro & Boldyrev 2017;Agudelo Rueda et al 2021.…”