Downstream structures of interplanetary fast shocks associated with coronal mass ejections

We investigate 17 coronal mass ejection (CME) events identified by the ACE spacecraft during solar cycle 23, focusing upon the fine structures of the sheath region between the CME and its associated shock to find their dependence on the shock parameters. We observe the planar magnetic structure (PMS) downstream of a quasi-perpendicular shock when the Alfven Mach number > 2.0. Here, the PMS is characterized by the magnetic fields changing directions abruptly and intermittently within a plane parallel to the shock plane. The downstream PMS does not form when a magnetic cloud with beta value < 0.05 exists just upstream of a shock with Alfven Mach number < 2.0. The sheath magnetic fields become highly turbulent when the shock angle is < 60 and/or the upstream beta value is > 0.5 and the upstream is dominated by Alfvenic fluctuations.