Propagation of large-scale solar wind events in the outer heliosphere from a numerical MHD simulation

摘要

Voyager 1 occasionally detected sudden jumps of the local interstellar magnetic field strength since its heliopause crossing in August 2012.These events were believed to be associated with outward propagating solar wind shocks originating in the inner heliosphere.Here we investigate the correlation between interstellar shocks and large-scale solar wind events by means of numerical MHD simulation.The solar wind is simplified as a symmetric flow near the equatorial plane,and the interstellar neutrals are treated as a constant flow with a fixed density distribution along the upwind direction of the local interstellar medium.The charge exchanges between the solar wind plasma and the interstellar neutrals are taken into account.At a heliocentric distance of 1 AU,the solar wind data from OMNI,STEREO A and B during the period between 2010 and 2017 are used as the inner boundary conditions to drive the simulation.The simulation results showed that the solar wind gradually merges into large-scale structures as the radial distance increases,consistent with observations by New Horizons.After propagating into the inner heliosheath,the shocks are fully developed and the corresponding pressure pulses roughly agree with the observations by Voyager 2 in the inner heliosheath.The arrival of the shocks beyond the heliopause is estimated and found to be consistent with the observed signatures of interstellar shocks by Voyager 1.The possible origins of interstellar shocks in the inner heliosheath are discussed based on the simulation.