Formation and Structure of Intermediate Shocks in Collisionless Plasmas

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9224553 Karimabadi Of the six types of shocks (fast, slow, and four types of intermediate shocks) allowed by magnetohydrodynamic (MHD) Rankine- Hugoniot relations, intermediate shocks are the least understood. Besides being of great theoretical interest, the study of intermediate shocks (ISs) is essential to the understanding of diverse space plasma phenomena, such as the magnetopause and shock fronts associated with coronal mass ejections. ISs provide an important dissipation process in space plasmas and are one of only two plasma discontinuities that allow for the rotation of the magnetic field, with the other being the rotational discontinuity (RD). Although the existence of ISs has recently been established within the resistive MHD framework, far less is known about their properties in collisionless plasmas. This work is to investigate the formation and properties of ISs and their relation to RDs in collisionless plasmas with applications to space plasmas. For the first time many important effects, such as temperature anisotropy, will be included in the calculations. We will examine the hypothesis that field rotations at the magnetopause and in the solar wind are due to ISs rather than RDs. Two approaches will be taken. One is the study of ISs as a single structure removed from external perturbations. The other approach involves the formation of multiple discontinuities and their interactions, much as would occur during reconnection events. The goal of this study is to determine the conditions under which ISs can be formed, and whether they can remain stable in the presence of perturbations. The primary tools of our investigation are state-of-the-art kinetic numerical simulations, although for comparison, MHD simulations will also be performed. ***