[P-EM16] Heliosphere and Interplanetary Space

[PEM16-06] Dependence of plasma properties on the pickup ion density in the heliosheath

*Ken Tsubouchi¹ (1.University of Electro-Communications)

Keywords:heliosheath, pickup ion, solar wind, termination shock

The heliosphere is surrounded by the termination shock (TS) and the heliopause (HP), the interface between the solar wind and interstellar plasma. The heliosheath (HS) is a region enclosed by these boundaries. It is filled with plasma that is the supersonic solar wind decelerated and heated at the termination shock. The passage positions of Voyager 1 and 2 through the HP and TS respectively indicate the pronounced north-south asymmetry of the heliosphere, particularly at the TS. Assuming a uniform interstellar environment, this asymmetry can be understood as differences in the plasma environment in the heliosheath. Since the plasma characteristics within the HS are determined by the heating process of the solar wind at the TS, it is necessary to verify the relationship with solar wind parameters. In this study, we focus on the dynamics of pickup ions (PUIs), which contribute to most of the energy density in the outer heliosphere. By conducting hybrid simulations introducing a one-dimensional shock tube model that discontinuously contacts solar wind plasma and interstellar plasma in systems containing PUIs, we verify the dependence of PUI density on parameters such as the energy distribution of plasma formed within the heliosheath. We further discuss the thermodynamic processes within the heliosheath by comparing polytropic indices directly derived from computational results, aiming to quantify the impact on the heliospheric structure.