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

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 (similar to 10(5) km) ultra-low-frequency waves and microscale (similar to 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-waveinduced 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 efficientmechanism for cross-scale energy transfer and plasma energization in astrophysical and space plasmas.

Automated summary

Identifying the energy transfer from macroscales to microscales in collisionless plasmas is crucial for astrophysics and space physics. Two cross-scale energy-transfer events observed in Earth's magnetosphere demonstrate the efficiency and timescale of this process, where hot ions interact with ultra-low-frequency waves and electromagnetic-ion-cyclotron waves.