The Development of a Split-tail Heliosphere and the Role of Non-ideal Processes: A Comparison of the BU and Moscow Models

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.

The Structure of the Large-Scale Heliosphere as Seen by Current Models

“…As shown by Kornbleuth et al. ( 2021b ), the shape of both the split-tail and comet-tail models agree at the nose. Kornbleuth et al.…”

“…Kornbleuth et al. ( 2021b ) compared the heliospheric solutions of the BU model and the Moscow model, which suppresses magnetic reconnection at the heliopause, and showed that regardless of heliopause treatment both models show a confinement of the solar wind plasma by the solar magnetic field (Fig. 14 ).…”

“…Recently it was settled that among different models, as BU, and Moscow Kornbleuth et al. ( 2021b ) (both with kinetic treatment of neutrals and same latitudinal solar wind) the heliotail plasma was confined by the solar magnetic field. The difference resides in that in the BU model at 400 au downtail the ISM flows in between the two confined jets while in the Moscow model the two jets are embedded in a long comet-like tail.…”

“…( 2021 ) and Kornbleuth et al. ( 2021b ) used a kinetic neutral treatment with uniform and latitudinally-varying solar wind conditions, respectively, in the BU model and both works found that a “croissant-like” shape persists even in the presence of a kinetic neutral treatment.…”

On the Energization of Pickup Ions Downstream of the Heliospheric Termination Shock by Comparing 0.52–55 keV Observed Energetic Neutral Atom Spectra to Ones Inferred from Proton Hybrid Simulations

“…PUIs with parameter κ = 10 (1.57), density = , where n p is the plasma density and E p is the thermal energy of the plasma extracted from the BU MHD model of Kornbleuth et al (2021b). These fits are depicted with dashed lines in Figure 1 (green for SW, blue for transmitted PUIs, and red for the reflected and energized PUIs).…”