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Keywords:

  • dipolarization;
  • flow-braking region;
  • mirror instability;
  • plasma sheet;
  • shocklet;
  • temperature anisotropy

[1] We investigate the small-scale structure of jet fronts through a case study of multi-spacecraft Cluster observations in the near-Earth flow-braking region at ∼−10 RE. We find that the interaction between the earthward moving fast plasma jet and the high-β ambient plasma in the plasma sheet results in magnetic pileup and compression ahead of the jet and rarefaction trailing the jet. It is shown that mirror-mode structures of ion gyroradius scale develop within the pileup region due to the observed ion temperature anisotropy (Ti > Ti). We suggest that the growth of these mirror modes is driven by the perpendicular total pressure perturbation (Δp) generated by the braking jet. When Δp becomes too large, the mirror-mode structure cannot maintain pressure balance any longer, and consequently a shocklet is formed in the pileup region ahead of the jet front. We present the first evidence for such a kinetic shocklet in the flow-braking region.