Abstract
Abstract. Beams of Almost Monoenergetic Ions (AMI) in the energy range from 20 to 800 keV were discovered in the DOK-2 experiment (Interball project) in the magnetosheath and upstream of the Earth's bow shock. This work summarizes the analysis results of ~730 AMI events registered in 1995–2000. Statistics of AMI properties, their nature and origin are considered. The analysis of a large array of new data confirmed our earlier suggested ideas on the AMI nature, origin, and their acceleration model. These ideas were further developed and refined. According to this model, AMI are a result of solar wind ions acceleration in small regions with a potential electric field arising due to disruptions of the bow shock current sheet filaments. It has been found that the reason of the current filaments disruptions in most cases was the Hot Flow Anomaly phenomenon (HFA) caused by an interaction of a tangential discontinuity in the solar wind with the Earth's bow shock. It is shown that the study of AMI can provide new information on large-scale properties and dynamics of the bow shock current sheet.
Highlights
Ions and electrons accelerated in the near-Earth plasma in the energy range of 20 keV to 1000 keV usually have smooth spectra with a negative slope
According to this hypothesis Almost Monoenergetic Ions (AMI) are a result of solar wind ions acceleration by bursts of strong potential electric fields in small parts of current sheets in the magnetosphere and on its boundaries
A sum of the electromotive force of the circuit (EMF) and the self-inductance EMF (B in Fig. 15) will be applied to the short disruption interval W as a voltage difference V = A + B. This assumption was entirely confirmed by the results of our full analysis of the ∼730 AMI events, in particular: 1. by the positions of AMI observation points, 2. by the energy ratios of AMI lines corresponding to the ratios of H, He, and the CNO-group charges, 3. by the average energy of the proton line, which is not inconsistent with the average potential drop across the magnetosphere due to the motional electric field of the solar wind: Esw = −(V sw × Bsw), 4. by short durations of AMI events, 5. by the character of time variations of proton line energies and intensities at the event start
Summary
Ions and electrons accelerated in the near-Earth plasma in the energy range of 20 keV to 1000 keV usually have smooth spectra with a negative slope. Note that in energetic electron spectra measured with the same resolution narrow lines were observed only in the dispersion events (Lutsenko et al, 2005, 2008) associated with the acceleration processes in the plasma sheet of the magnetospheric tail. In our previous papers we have published results based on the analysis of the limited number of AMI events and suggested a hypothesis about their nature and origin According to this hypothesis AMI are a result of solar wind ions acceleration by bursts of strong potential electric fields in small parts of current sheets in the magnetosphere and on its boundaries. To find the reasons for current disruptions As it was noted, the discovery and study of AMI became possible owing to the record high energy and time resolutions of the DOK-2 instrument (Lutsenko et al, 1998). At high particle fluxes the spectrum accumulation time was reduced to 2–5 s, and at low fluxes it increased, but not more than Tmax
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