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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 36, issue 3 | Copyright
Ann. Geophys., 36, 879-889, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Regular paper 15 Jun 2018

Regular paper | 15 Jun 2018

Magnetic depression and electron transport in an ion-scale flux rope associated with Kelvin–Helmholtz waves

Binbin Tang1, Wenya Li2,1, Chi Wang1, Lei Dai1, Yuri Khotyaintsev2, Per-Arne Lindqvist3, Robert Ergun4, Olivier Le Contel5, Craig Pollock6, Christopher Russell7, and James Burch8 Binbin Tang et al.
  • 1State Key Laboratory of Space Weather, National Space Science Center, Chinese Academy of Sciences, Beijing, China
  • 2Swedish Institute of Space Physics, Uppsala, Sweden
  • 3KTH Royal Institute of Technology, Stockholm, Sweden
  • 4Laboratory for Atmospheric and Space Physics, University of Colorado Boulder, Boulder, Colorado, USA
  • 5Laboratoire de Physique des Plasmas, CNRS, Ecole polytechnique, UPMC Univ Paris 06, Univ. Paris-Sud, Observatoire de Paris, Paris, France
  • 6NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
  • 7Department of Earth and Space Sciences, University of California, Los Angeles, California, USA
  • 8Southwest Research Institute, San Antonio, Texas, USA

Abstract. We report an ion-scale magnetic flux rope (the size of the flux rope is  ∼ 8.5 ion inertial lengths) at the trailing edge of Kelvin–Helmholtz (KH) waves observed by the Magnetospheric Multiscale (MMS) mission on 27 September 2016, which is likely generated by multiple X-line reconnection. The currents of this flux rope are highly filamentary: in the central flux rope, the current flows are mainly parallel to the magnetic field, supporting a local magnetic field increase at about 7nT, while at the edges the current filaments are predominantly along the antiparallel direction, which induce an opposing field that causes a significant magnetic depression along the axis direction (>20nT), meaning the overall magnetic field of this flux rope is depressed compared to the ambient magnetic field. Thus, this flux rope, accompanied by the plasma thermal pressure enhancement in the center, is referred to as a crater type. Intense lower hybrid drift waves (LHDWs) are found at the magnetospheric edge of the flux rope, and the wave potential is estimated to be  ∼ 17% of the electron temperature. Though LHDWs may be stabilized by the mechanism of electron resonance broadening, these waves could still effectively enable diffusive electron transports in the cross-field direction, corresponding to a local density dip. This indicates LHDWs could play important roles in the evolution of crater flux ropes.

Publications Copernicus
Short summary
The Kelvin–Helmholtz waves are believed to be an effective way to transport solar wind mass and energy into Earth's magnetosphere. In this study, we show that the ion-scale flux rope generated at the trailing edge of Kelvin–Helmholtz waves by multiple X-line reconnection could be directly related to this transfer process. The lower hybrid drift waves detected at the edges of the flux rope can also contribute to this process and then affect the revolution of the flux rope.
The Kelvin–Helmholtz waves are believed to be an effective way to transport solar wind mass and...