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

Abstract

This review summarizes the current state of research aiming at a description of the global heliosphere using both analytical and numerical modeling efforts, particularly in view of the overall plasma/neutral flow and magnetic field structure, and its relation to energetic neutral atoms. Being part of a larger volume on current heliospheric research, it also lays out a number of key concepts and describes several classic, though still relevant early works on the topic. Regarding numerical simulations, emphasis is put on magnetohydrodynamic (MHD), multi-fluid, kinetic-MHD, and hybrid modeling frameworks. Finally, open issues relating to the physical relevance of so-called “croissant” models of the heliosphere, as well as the general (dis)agreement of model predictions with observations are highlighted and critically discussed.

Observations of the Outer Heliosphere, Heliosheath, and Interstellar Medium

“…All produce insufficient heliosheath thinning, as discussed in Kleimann et al. ( 2022 , this journal)…”

“…Steady state MHD simulations give widths of 55–65 AU (see Kleimann et al. 2022 , this journal). This difference implies that time dependence is important or that pressure is missing from the heliosheath; mechanisms suggested to resolve this problem are solar cycle variations (Izmodenov et al.…”

“…The lack of field rotation is still a puzzle and discussed in the modeling chapter (Kleimann et al. 2022 ).…”

“…The shape of the heliotail is controversial, with model predictions ranging from a spherical HP to a HP with a long comet-like tail (see Kleimann et al. 2022 , this journal). Even inside these boundaries the LISM has a major influence on the solar wind.…”

Backscattered Solar Lyman-$\alpha $ Emission as a Tool for the Heliospheric Boundary Exploration

“…Modern versions of the hot model of the interstellar hydrogen distribution in the heliosphere, such as the models by Katushkina et al [2015b] and Kubiak et al [2021a,b], take into account both the solar cycle and heliolatitudinal variations of the solar wind and the disturbances of the hydrogen flow by the heliospheric interface. Kleimann et al [2022] presents an overview of the current state of research in global modelling of the heliospheric interface. Galli et al [2022] summarizes all direct observations of interstellar H atoms (and other neutrals), most of which were acquired with the Interstellar Boundary Explorer (IBEX) launched in 2008.…”