SLAMS at parallel shocks and hot flow anomalies

We present a review of Cluster observations of two bow shock phenomena, using data from a range of tetrahedron scales. The first are SLAMS: magnetic field enhancements embedded within the quasi-parallel shock transition. They are thought to play an essential role in plasma thermalisation at shocks. We show that their overall size exceeds 1000 km, but that they have internal structure on scales of ~150 km, and that they evolve on time scales of a few seconds. The second phenomena are Hot Flow Anomalies (HFAs): regions of explosively expanding hot plasma generated by the interaction of a tangential discontinuity with the bow shock. We explore the shape and evolution of HFAs. Small spacecraft separation scales are particularly suited for examining the boundary motion and orientation of these structures, and we demonstrate the occurrence of shocks at the edges of the expanding HFA bubble, and compare their orientations with the estimated orientation of the underlying discontinuity. Observations at large scales are appropriate for the examination of the time evolution of the HFA structure: we show an example upstream of the bow shock in the flank region when the four spacecraft observed the evolution of shocks from compressions at the HFA edges.

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