Tangential discontinuities as diagnostics for disordered (e.g. quasi-parallel) shocks

Using the 1 min CLUSTER data publicly available, we examine the ability of discrete structures, i.e. tangential or rotational discontinuities, to survive quasi-perpendicular and quasi-parallel shocks. As expected theoretically, discontinuities survive the quasi-perpendicular shocks. Surprisingly, in spite of the parallel shock re-formation and large disordered fields, discontinuities also seem to survive parallel shocks. This certainly must have theoretical implications to help our understanding of the physical processes behind parallel shocks; a process not yet completely clear. We also show that these discontinuities can also tell us when the spacecraft is in pre-shock plasma and when it is in post-shock plasma, hence providing an approximate shock location. In the same way, we can identify the magnetopause because the discontinuities vanish when the spacecraft enters it, and frequently the discontinuity there is unusually strong, possibly being the magnetopause itself. There are at least three signatures for a quasi-parallel shock that can be seen in 1 min data: little or no increase in the vector magnetic field components, large magnetic field fluctuations (comparable to ambient), and fluctuations seen well into the magnetosphere.