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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 36, issue 3
Ann. Geophys., 36, 741-760, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Ann. Geophys., 36, 741-760, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Regular paper 17 May 2018

Regular paper | 17 May 2018

Contrasting dynamics of electrons and protons in the near-Earth plasma sheet during dipolarization

Andrey Y. Malykhin1, Elena E. Grigorenko1,2, Elena A. Kronberg3,4, Rositza Koleva5, Natalia Y. Ganushkina6,7, Ludmila Kozak8,9, and Patrick W. Daly3 Andrey Y. Malykhin et al.
  • 1Space Research Institute of RAS, Moscow, Russia
  • 2Moscow Institute of Physics and Technology, Moscow, Russia
  • 3Max Planck Institute for Solar System Research, Göttingen, Germany
  • 4Ludwig Maximilian University of Munich, Munich, Germany
  • 5Space Research and Technologies Institute of BAS, Sofia, Bulgaria
  • 6Finnish Meteorological Institute, Helsinki, Finland
  • 7University of Michigan, Ann Arbor, MI, USA
  • 8Kyiv Taras Shevchenko University, Kiev, Ukraine
  • 9Space Research Institute National Academy of Sciences of Ukraine and State Space Agency of Ukraine, Kiev, Ukraine

Abstract. The fortunate location of Cluster and the THEMIS P3 probe in the near-Earth plasma sheet (PS) (at X  ∼ −7–−9 RE) allowed for the multipoint analysis of properties and spectra of electron and proton injections. The injections were observed during dipolarization and substorm current wedge formation associated with braking of multiple bursty bulk flows (BBFs). In the course of dipolarization, a gradual growth of the BZ magnetic field lasted  ∼ 13min and it was comprised of several BZ pulses or dipolarization fronts (DFs) with duration  ≤ 1min. Multipoint observations have shown that the beginning of the increase in suprathermal ( > 50keV) electron fluxes – the injection boundary – was observed in the PS simultaneously with the dipolarization onset and it propagated dawnward along with the onset-related DF. The subsequent dynamics of the energetic electron flux was similar to the dynamics of the magnetic field during the dipolarization. Namely, a gradual linear growth of the electron flux occurred simultaneously with the gradual growth of the BZ field, and it was comprised of multiple short ( ∼  few minutes) electron injections associated with the BZ pulses. This behavior can be explained by the combined action of local betatron acceleration at the BZ pulses and subsequent gradient drifts of electrons in the flux pile up region through the numerous braking and diverting DFs. The nonadiabatic features occasionally observed in the electron spectra during the injections can be due to the electron interactions with high-frequency electromagnetic or electrostatic fluctuations transiently observed in the course of dipolarization.

On the contrary, proton injections were detected only in the vicinity of the strongest BZ pulses. The front thickness of these pulses was less than a gyroradius of thermal protons that ensured the nonadiabatic acceleration of protons. Indeed, during the injections in the energy spectra of protons the pronounced bulge was clearly observed in a finite energy range  ∼ 70–90keV. This feature can be explained by the nonadiabatic resonant acceleration of protons by the bursts of the dawn–dusk electric field associated with the BZ pulses.

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