MHD MODELING OF THE OUTER HELIOSPHERIC STRUCTURES AROUND THE HELIOPAUSE

Abstract

Voyager 1 (V1) observed the first step increase of the galactic cosmic ray (GCR) flux for energies >70 MeV and >211 MeV near the heliopause at 2012.31, just before the magnetic field polarity changed from away to toward at 2012.47. This event was not accompanied by an anomalous cosmic ray (ACR) flux change. The second GCR step increase, together with an ACR decrease, was observed at 2012.65. The magnetic field change was observed with its polarity changing from a toward to an apparent away direction at 2012.56, at ~122 AU from the Sun, with an eventual orientation of 22°. The later magnetic field has been identified as the interstellar magnetic field and the current sheet at the polarity change is identified as the boundary of the interstellar magnetic field. We present a three-dimensional stationary MHD simulation with a heliopause located at ~122 AU and a magnetic field polarity change across the heliopause. The apparent away polarity of the magnetic field is confirmed to be that of the interstellar magnetic field in this simulation. We present a detailed analysis of the magnetic field line topology in the vicinity of the heliopause and argue for a favorable condition of the first GCR step increase with no concurrent ACR flux change before the time corresponding to the magnetic polarity change at 2012.47.