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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/angeo-2019-54
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/angeo-2019-54
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Regular paper 09 Apr 2019

Regular paper | 09 Apr 2019

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This discussion paper is a preprint. A revision of this manuscript was accepted for the journal Annales Geophysicae (ANGEO) and is expected to appear here in due course.

Acceleration of protons and heavy ions to suprathermal energies during dipolarizations in the near-Earth magnetotail

Andrei Yu. Malykhin1,2, Elena E. Grigorenko1,2,3, Elena A. Kronberg4,5, Patrick W. Daly4, and Ludmila V. Kozak6,7 Andrei Yu. Malykhin et al.
  • 1Space Research Institute of Russian Academy of Sciences, Moscow, Russia
  • 2St. Petersburg State University, Saint Petersburg, Russia
  • 3Department of Space Physics, Moscow Institute of Physics and Technology, Moscow, Russia
  • 4Max Planck Institute for Solar System Research, Göttingen, Germany
  • 5Ludwig Maximilian University of Munich, Munich, Germany
  • 6Kyiv Taras Shevchenko University, Kyiv, Ukraine
  • 7Space Research Institute National Academy of Sciences of Ukraine and State Space Agency of Ukraine, Kyiv, Ukraine

Abstract. In this work we present an analysis of the dynamics of suprathermal ions of different masses (H+, He+, O+) during prolonged dipolarizations in the near-Earth magnetotail (X > −17 RE) according to Cluster/RAPID observations in 2001–2005. All dipolarizations from our data base were associated with fast flow braking and consisted of multiple dipolarization fronts (DFs). We found statistically that fluxes of suprathermal ions started to increase ~ 1 min before the dipolarization onset and continued to grow during ~ 1 min after the onset. The start of flux growth coincided with the beginning of decrease in the spectral index γ. The decrease in γ was observed for protons during ~ 1 min after the dipolarization onset, and for He+ and O+ ions - during ~ 3 min and ~ 5 min after the onset respectively. The negative variations of γ for O+ ions were in ~ 2.5 times larger than for light ions. This demonstrates more efficient acceleration for heavy ions. The strong negative variations of γ were observed in finite energy ranges for all ion components. This indicates the possibility of non-adiabatic resonant acceleration of ions in the course of their interaction with multiple DFs during dipolarizations. Our analysis showed that some fraction of light ions can be accelerated up to energies ≥ 600 keV and some fraction of oxygen ions can be accelerated up to ~ 1.2 MeV. Such strong energy gains cannot be explained by acceleration at a single propagating DF, and suggest the possibility of multistage ion acceleration in the course of their interaction with multiple DFs during the prolonged dipolarizations.

Andrei Yu. Malykhin et al.
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Andrei Yu. Malykhin et al.
Andrei Yu. Malykhin et al.
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Short summary
In this work we present an analysis of the dynamics of suprathermal ions of different masses (H+, He+, O+) during prolonged dipolarizations in the near-Earth magnetotail according to Cluster/RAPID observations in 2001–2005. All dipolarizations from our data base were associated with fast flow braking and consisted of multiple dipolarization fronts (DFs). We found statistically that fluxes of suprathermal ions started to increase ~ 1 min before the dipolarization onset and continued.
In this work we present an analysis of the dynamics of suprathermal ions of different masses...
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