Abstract
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 interstellar medium (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.
Highlights
The heliosphere is formed through the interaction between the solar wind and the interstellar medium (ISM) as the Sun moves through its local environment
The low latitude region of the tail in the BU model is dominated by ISM plasma while the heliopause in the Moscow model prevents penetration of ISM into this region
The BU model flows stagnate in this region, which does not occur in the Moscow model
Summary
The heliosphere is formed through the interaction between the solar wind and the interstellar medium (ISM) as the Sun moves through its local environment. In the model of Izmodenov & Alexashov (2015) and Izmodenov & Alexashov (2020) ( referred to as the Moscow model), reconnection between the interstellar and solar magnetic fields at the heliopause is not allowed by their numerical approach. The two numerical models of the heliosphere used in this work are the Moscow model (Izmodenov & Alexashov 2015; Izmodenov & Alexashov 2020) and the BU model (Opher et al 2015; Michael et al 2021) Both models are 3D kinetic-MHD models which treat the cold solar wind plasma and hot pick-up ion plasma as a single fluid, while treating neutral particles kinetically. Both models use the same inner boundary conditions for the solar wind (Figure 1), an averaged solar cycle condition from the years 1995 to 2017 and the same outer boundary conditions for the interstellar neutral H and protons (Izmodenov & Alexashov 2020)
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