The development of a split-tail heliosphere and the role of non-ideal processes: a comparison of the BU and Moscow models

TL;DR

This study compares two 3D MHD heliosphere models, BU and Moscow, highlighting how different physical assumptions and numerical treatments influence the predicted structure and magnetic interactions of the heliosphere.

Contribution

It provides a direct comparison of two global heliosphere models with identical boundary conditions, emphasizing the impact of magnetic reconnection and numerical approaches on heliospheric structure.

Findings

BU model predicts a thinner heliosheath by 15%.

Different magnetic draping causes variations in ISM pressure and boundary locations.

Reconnection affects the heliosphere's magnetic topology and boundary shape.

Abstract

Global models of the heliosphere are critical tools used in the interpretation of heliospheric observations. There are several three-dimensional magnetohydrodynamic (MHD) heliospheric models that rely on different strategies and assumptions. Until now only one paper has compared global heliosphere models, but without magnetic field effects. We compare the results of two different MHD models, the BU and Moscow models. Both models use identical boundary conditions to compare how different numerical approaches and physical assumptions contribute to the heliospheric solution. Based on the different numerical treatments of discontinuities, the BU model allows for the presence of magnetic reconnection, while the Moscow model does not. Both models predict collimation of the solar outflow in the heliosheath by the solar magnetic field and produce a split-tail where the solar magnetic field confines the charged solar particles into distinct north and south columns that become lobes. In the BU model, the ISM flows between the two lobes at large distances due to MHD instabilities and reconnection. Reconnection in the BU model at the port flank affects the draping of the interstellar magnetic field in the immediate vicinity of the heliopause. Different draping in the models cause different ISM pressures, yielding different heliosheath thicknesses and boundary locations, with the largest effects at high latitudes. The BU model heliosheath is 15% thinner and the heliopause is 7% more inwards at the north pole relative to the Moscow model. These differences in the two plasma solutions may manifest themselves in energetic neutral atom measurements of the heliosphere.