Jet front-driven mirror modes and shocklets in the near-Earth flow-braking region

• 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 similar to-10 RE. We find that the interaction between the earthward moving fast plasma jet and the high-beta 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 (T(i perpendicular to) > T(i parallel to)). We suggest that the growth of these mirror modes is driven by the perpendicular total pressure perturbation (Delta p(perpendicular to)) generated by the braking jet. When Delta p(perpendicular to) 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.

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NATURVETENSKAP  -- Fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences (hsv//eng)

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