Propagation of Large-Scale Solar Wind Events in the Outer Heliosphere From a Numerical MHD Simulation

Abstract

Voyager 1 occasionally detected the sudden jumps of the local interstellar magnetic field strength since its heliopause crossing in August 2012. These events were believed to be associated with the outward propagating shocks that had the solar wind origin in the inner heliosphere. Here we investigate the correlation between the interstellar shocks and the large-scale solar wind events by means of the 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-exchange 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 the year 2010 and 2017, are used as the inner boundary conditions to drive the simulation. The simulation results showed that the solar wind gradually merge into large-scale structures as the radial distance increases, being consistent with the observations by New Horizons. After propagating into the inner heliosheath, the shocks are fully developed and the corresponding pressure pulses roughly agree with the observation by Voyager 2 in the inner heliosheath. The arrival of the shocks beyond heliopause are estimated and found to be consistent with the observed signatures of interstellar shocks by Voyager 1. The possible origins of the interstellar shocks in the inner heliosheath are discussed based on the simulation.

Observations of the Outer Heliosphere, Heliosheath, and Interstellar Medium

“… 2017 ; Guo et al. 2021 ). These recent models have the advantage of including the termination shock, heliosheath and heliopause, but face difficulties such as how to determine the 3D solar wind input, and reproduce correct locations of the heliospheric structures and precise timing with the Voyager 1 measurements.…”

Effects of anomalous cosmic rays on the solar wind events in the outer heliosphere

“…For better comparison, the positions of New Horizons, Voyager 1 and 2 are marked in the figure. These three spacecrafts are assumed to move upwind toward the intestellar neutrals, which is roughly consistent with the reality (Guo et al, 2021). Note that Voyager 1 is approaching the heliopause which is located at 121.6 AU from the later observation, the termination shock is at about 81 AU at the time.…”

“…Richardson et al (2017) found that the pressure pulses detected by Voyager 2 in the heliosheath are correlated with the interstellar shocks by Voyager 1. Based on a spherically symmetric MHD model containing termination shocks, Guo et al (2021) performed the numerical simulations using three solar wind sources (STEREO A and B, and OMNI) with different longitudes as inner boundary conditions, and did comparison analyses with the in situ observations of New Horizons, Voyager 1 and 2 in the outer heliosphere. Their results indicate the possible connection between the pressure pulse observed by Voyager 2 and the interstellar shock events observed by Voyager 1.…”

Shocks in the Very Local Interstellar Medium

“…Recently, Guo et al. ( 2021 ) extended their 1-D numerical MHD model by using inputs from OMNI, STEREO-A, and B at 1 AU and found that each of the plasma oscillations and shock events in the VLISM are linked to large-scale solar wind events. An observational study by Richardson et al.…”