Magnetic overshoots at heliospheric shocks: parameter studies

In the transition region of a collisionless shock, the magnetic field strength generally reaches a larger value than the eventual downstream one. The formation of this magnetic overshoot plays an important role in, e.g., regulating the ion reflection. The magnitude of the overshoot varies spatially and temporarily along the shock front, necessitating several measurements to quantify it.

Catalogues of in situ shock crossing observations are now readily available from across the whole heliosphere, enabling large statistical studies. Here we combine measurements from Earth, Mars, Saturn as well as interplanetary shocks in the inner heliosphere, to investigate how the magnitude of the overshoot depends on the upstream parameters.

Consistent with previous studies, we find that there is a clear relationship with the upstream Alfvén Mach number and the magnitude of the overshoot relative to the upstream field strength. In the low Mach number (< 4) range, however, there appears to be an intriguing difference between planetary and interplanetary shocks. In contrast to past studies, we find that the overshoot does not depend on the upstream plasma beta for a given Alfvén Mach number.