Observations of Earth’s bow shock with very high β>10 (ratio of thermal
to magnetic pressure) are extremely rare.
However, such shocks are supposed to be ubiquitous in astrophysical plasmas.
We present statistics of several tens β>10 shocks for MMS, Cluster and Geotail,
26 of which have β>30. For the latter subset the most of
crossings reveal very complex structure with quasi periodic shocklets,
gradually thermalising the solar wind ion flow. One fortuitous MMS shock event
allowed to study this phenomenon with unprecedented details. Each shocklet, in turn, consists
of very high-amplitude magnetic oscillations with the period about 1 sec, coupled with the pulses of the plasma flow. These variations have wavelength about 150 km and are almost standing in the plasma rest frame, consistent with the expectation for Weibel mode.
All together, the transition interval may last 5–10 min, but corresponds to a proton cyclotron scale in the solar wind,
due to very low magnetic field and very slow shock motion.