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Keywords:

  • solar wind;
  • interplanetary shock;
  • ion scale

[1] A formation of low-Mach-number quasi-perpendicular shocks is expected to be well understood. From theoretical considerations as well as from observations, it follows that the shock ramp thickness would scale with the ion inertial length. We present analysis of 12 subcritical or marginally critical interplanetary shocks that reveals that (1) the ion transition scale determined from direct measurements of plasma moments (speed, temperature, and density) are of the same order as the ramp thickness determined from the magnetic field and (2) the ion transition scale is directly proportional to the ion thermal gyroradius, Rth; it was found to be ≈3.2 Rth in a broad range of solar wind and shock parameters. These results stress a role of the ion kinetics in the shock formation.