Wave-particle interactions in the Earth magnetotail during dipolarization

The energy of particles in the Earth's magnetosphere changes significantly when the configuration of the magnetic field lines suddenly changes from stretched to more dipolar (dipolarization). Energy changes can be caused by variation in electric fields,  due to the generation of electrostatic waves, etc. The presence of heavy ions at the heights of the magnetosphere significantly changes the physics of the processes since, in addition to changing the main characteristics of the plasma (temperature, pressure, Alfven velocity thickness of the current/plasma layer), the conditions and rate of development of instabilities (in particular, the Kelvin-Helmholtz instability) and the nature of turbulent processes will change as well.

In this work, the change of ion and electron fluxes is considered and the peculiarities of resonant interaction of charged particles with electromagnetic fluctuations during the dipolarizations are determined.

The data from the Cluster-II mission spacecraft (magnetic field measurements from ferroelectrode magnetometers (FGM) and energetic particle fluxes from RAPID spectrometers) were used for the analysis. The analysis of individual events is carried out, and a statistical consideration of changes in particle fluxes during magnetic field dipolarizations for 2001–2015 is presented.

Among the features of proton fluxes for individual events, an non-correlation between flux changes in different energy channels is recorded (example, the flux at 27 keV is approximately constant, and is peaks in higher energy ranges). Thus, we have a selective non-adiabatic acceleration of a part of a proton spectrum depending on energy. The change of the spectral index for different energy channels and components was studied.

The values of the power of magnetic field oscillations at gyrofrequencies for different ion types obtained by epoch superposition method showed that resonant interactions of ions with low-frequency electromagnetic waves are more significant for "heavier" components. Therefore the ions can effectively be accelerated by the interaction with these waves during the dipolarization.

This work was supported by the grant no. 97742 of the Volkswagen Foundation (VW-Stiftung), the Royal Society International Exchanges Scheme 2021 IES\R1\211177, and BF/30-2021.