THREE-DIMENSIONAL FEATURES OF THE OUTER HELIOSPHERE DUE TO COUPLING BETWEEN THE INTERSTELLAR AND INTERPLANETARY MAGNETIC FIELDS. I. MAGNETOHYDRODYNAMIC MODEL: INTERSTELLAR PERSPECTIVE

摘要

The properties of the Local Interstellar Cloud (LIC) are rather poorly examined, with the exception of the interstellar plasma velocity and temperature. The poorest known quantities are the strength and direction of the interstellar magnetic field (ISMF). We review available observational data and perform three-dimensional, time-dependent parametric modeling of the solar wind (SW) interaction with the local interstellar medium (LISM) for a number of typical strengths and directions of the ISMF. The effect of coupling the ISMF and the interplanetary magnetic field on the SW-LISM interaction pattern is investigated. In addition, we consider the case of an ISMF vector perpendicular to the LISM velocity vector and inclined at an angle of 60° toward the ecliptic plane, as suggested in recent publications relating LIC properties to the radio emission observed by Voyager 1. Since the existence of nonevolutionary MHD shocks remains controversial, special attention is paid to the case where the ISMF strength ahead of the bow shock falls into the region of nonevolutionary parallel shocks. It is shown that a complicated, multishocked solution, which exists in this case in the axially symmetric statement, acquires a regular evolutionary structure in a genuinely three-dimensional formulation of the problem. Current views regarding the existence and character of nonevolutionary shocks in space are presented, and an attempt is made to distinguish important physical questions of the uniqueness of MHD shock-wave structures from numerical artifacts. This is the first in a series of papers investigating the three-dimensional structure of the outer heliosphere. Here we present the results of purely MHD calculations, adopting an interstellar medium perspective. Subsequent papers will address the combined effect of charge exchange between neutral and charged particles and magnetic fields.