Abstract

Current sheets are phenomena of general occurrence in space plasmas where they form at the boundaries between plasmas and/or magnetic fields of different origin. Examples beyond the Earth's magnetospheres are heliospheric and planetary magnetospheric current sheets or coronal filaments. While the global properties of the Earth's magnetotail current sheet can be well understood as a MHD-scale process resulting from the interaction between the interplanetary magnetic field (IMF) carried by the solar wind and the Earth's intrinsic field, most dramatic energy conversion processes takes place when thin current sheets are formed with a thickness below several ion inertia lengths. An example is magnetic reconnection, which is one of the key process occuring in a thin current sheet. Here magnetic field energy is converted into particle energy and can affect the large-scale dynamics of the Earth's magnetotail, leading to explosive energy dissipation during substorms and magnetic storms. The proposed study aims at a comprehensive understanding of thin current sheet processes by examining its properties under different condition, i.e. during rather stable configuration and during active current sheets when reconnection is taking place. Furthermore, the transition phase between quiet and active thin current sheets are studied, which is a more challenging but a fundamental problem in the thin current sheet process. The three key science questions are: (1) How are thin current sheets formed? (2) How does the thin current sheet activate and how does reconnection start? (3) How are thin current sheets structured in the reconnection region? The following three work packages are planned in this research to answer these key questions, based on extensive analysis of data obtained by multi-point observations by Cluster and THEMIS.

  • WP1. Analysis of a stable/quiet thin current sheet
  • WP2. Analysis of transition phase from quiet to disturbed current sheet (reconnection onset)
  • WP3. Analysis of an unstable/active thin current sheet

Multi-point data analysis is performed at different spatial/temporal scales by combining different approaches of thin current sheet investigation, i.e., stable current sheet analysis and dynamic current sheet analysis. The former analysis allows to understand the slow formation of the thin current sheet and its condition just before the activation, while the latter analysis serves to identify the different local configuration of the active current sheets and their temporal/spatial development in terms of change in the topology as well as resultant particle acceleration processes. The results from these complementary data analysis are compared with the appropriate theoretical models to make further implication on plausible mode of the instabilities or plausible scenario of the evolution of the thin current sheet.