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Chinese Journal of Space Science ›› 2018, Vol. 38 ›› Issue (2): 147-168.doi: 10.11728/cjss2018.02.147

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Ion-scale Structures in Flux Ropes Observed by MMS at the Magnetopause

LIU Yang1, PU Zuyin1, XIE Lun1, GUO Ruilong2, WANG Xiaogang3, XIAO Chijie4, SHI Quanqi5, DUNLOP M6, BOGDANOVA Y V6, MOORE T E7, RUSSELL C T8, LINDQVIST P A9, TORBERT R B10, POLLOCK C7, ZHAO Cong8   

  1. 1. School of Earth and Space Sciences, Peking University, Beijing 100871;
    2. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029;
    3. Department of Physics, Harbin Institute of Technology, Haerbin 150001;
    4. Institute of Plasma Physics and Fusion Studies, Peking University, Beijing 100871;
    5. School of Space Science and Physics, Shandong University, Weihai 264209;
    6. RAL Space, Rutherford Appleton Laboratory, STFC, Didcot, OX110 QX, UK;
    7. Goddard Space Flight Center, NASA, Greenbelt, MD, USA;
    8. University of California, Los Angeles, CA, USA;
    9. Royal Institute of Technology, Stockholm, Sweden;
    1
    0. University of New Hampshire, Durham, NH, USA
  • Received:2017-11-03 Revised:2017-11-24 Online:2018-03-15 Published:2018-03-09

Abstract:

In this paper the structures with scale of ion inertial length (di) in flux ropes at the magnetopause are studied based on MMS measurements. The results show that currents (jm) of di scale are found to exist in many flux ropes with different scales, which flow in the -M direction in magnetopause local coordinates (i.e., in the same direction of the Chapman-Ferraro current at the magnetopause) and are carried by electrons' motion in the +M direction (vem). Within the current structures, magnetosheath and magnetospheric plasma populations are mixed; the magnetic field has open topology; ions are non-magnetized, while electrons are frozen-in with the magnetic field lines; the N-component of electric field (En), which is Hall electric field in nature, substantially enhances (up to about 20mV·m-1), accompanying with notable fluctuations. Detailed analysis shows that the current, separation of electrons' motion from ions and the Hall electric field are closely related to each other, and obey the general Ohm's Law. In addition, we have also analyzed the MMS measurements of magnetic reconnection events at the magnetopause. It is found that structures similar to those in flux ropes are also present inside the reconnection region in many cases. Their scales are of di length. The directions (magnitudes) of the Hall electric field EN, current filament jM and electron velocity veM are as same as (close to) those in flux ropes. On the bases of above observations and making use of the classical flux rope models, how the di-scale structures in flux ropes are formed is studied. It is suggested that they are likely to originate from the corresponding structures in the reconnection region at the magnetopause which play an essential role in the formation process of di-scale flux ropes.

Key words: Magnetic flux ropes, Ion-scale current, Hall electric field, Magnetopause, Magnetic reconnection

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