Jacob Heerikhuisen

Probing Heliospheric Asymmetries with an MHD-Kinetic model

New solar wind data from the Voyager 1 and Voyager 2 spacecraft, together with the SOHO SWAN measurements of the direction in which neutral hydrogen enters into the inner heliosheath and neutral helium measurements provided by multiple observations, are expected to provide more reliable constraints on the ionization ratio of the local interstellar medium (LISM) and the direction and magnitude of the interstellar magnetic field (ISMF). In this Letter we use the currently most sophisticated numerical model of the heliospheric interface, which is based on an MHD treatment of the ion flow and kinetic modeling of neutral particles, to analyze an ISMF-induced asymmetry of the heliosphere in the presence of the interplanetary magnetic field and neutral particles. It is shown that secondary hydrogen atoms modify the LISM properties leading to its shock-free deceleration at the heliopause. We determine the deflection of hydrogen atoms from their original trajectory in the unperturbed LISM and show that it occurs not only in the plane defined by the ISMF and LISM velocity vectors, but also, to a lesser extent, perpendicular to this plane. We also consider the possibility of using 2-3 kHz radio emission data to further constrain the ISMF direction.

Comparing various multi-component global heliosphere models

Context. Modeling of the global heliosphere seeks to investigate the interaction of the solar wind with the partially ionized local interstellar medium. Models that treat neutral hydrogen self-consistently and in great detail, together with the plasma, but that neglect magnetic fields, constitute a sub-category within global heliospheric models. Aims. There are several different modeling strategies used for this sub-category in the literature. Differences and commonalities in the modeling results from different strategies are pointed out. Methods. Plasma-only models and fully self-consistent models from four research groups, for which the neutral species is modeled with either one, three, or four fluids, or else kinetically, are run with the same boundary parameters and equations. They are compared to each other with respect to the locations of key heliospheric boundary locations and with respect to the neutral hydrogen content throughout the heliosphere. Results. In many respects, the models’ predictions are similar. In particular, the locations of the termination shock agree to within 7% in the nose direction and to within 14% in the downwind direction. The nose locations of the heliopause agree to within 5%. The filtration of neutral hydrogen from the interstellar medium into the inner heliosphere, however, is model dependent, as are other neutral results including the hydrogen wall. These differences are closely linked to the strength of the interstellar bow shock. The comparison also underlines that it is critical to include neutral hydrogen into global heliospheric models.

Nearly incompressible theory and large scale flows

The nearly incompressible theory of hydrodynamics has been generalized to flows which include a time‐independent large‐scale inhomogeneous background, such as the solar wind (Hunana, Zank, Shaikh, Phys. Rev. E 74, 026302, 2006). In contrast with the homogeneous case, the expansion of the fully compressible Navier‐Stokes equations in powers of sonic Mach number leads at the lowest order to a new system of inhomogeneous equations (referred to as locally incompressible). In this work, we numerically investigate this new inhomogeneous description for two dimensional freely‐decaying turbulence. We concentrate on the decay of the power spectrum for density fluctuations with an inhomogeneous density background in one direction that is proportional to 1/r2. Nearly incompressible theory predicts that the density fluctuations δρ behave at the leading order as a passive scalar, with an additional source term produced by coupling to the large‐scale inhomogeneous background. In this preliminary work, it is shown that ...

Interstellar turbulence in the presence of kinetic neutral atoms

The local interstellar medium (LISM) is a relatively cool partially ionized plasma, where neutral hydrogen atoms out‐number plasma protons by about 3:1. Neutral hydrogen plays an important role in determining the structure of the heliosphere, which is created by the interaction of solar wind plasma with LISM plasma. A key feature of neutral atoms is that their mean free paths are large, compared to the length scale of the heliosphere, and their main form of interaction is through charge‐exchange with the plasma. For this reason it is generally accepted that heliospheric neutral atoms should be modeled kinetically, rather than as a fluid. In this paper we present preliminary results of a coupling between a kinetic neutral atom code and a 2D compressible MHD spectral code to investigate interstellar medium turbulence in the presence of kinetic neutral atoms.

Numerical simulations of primary and secondary hydrogen ENA fluxes at 1 AU

The interaction between the solar wind (SW) and the local interstellar medium (LISM) creates energetic neutral atoms (ENAs), mainly Hydrogen (H), at energies similar to ions in the SW. H ENAs are born from charge exchanges between SW protons and LISM H atoms. A large portion of measurable primary ENAs are born in the inner heliosheath (IHS), where the heated and condensed SW plasma has a large thermal component to direct ENAs back toward 1 AU. Secondary ENAs, however, require secondary charge exchanges before being detected at 1 AU. Primary ENAs born in the supersonic and subsonic SW may exit the HP, charge exchange into pick-up ions (PUIs), and charge exchange again to become secondary ENAs. Recent IBEX observations show a ribbon of flux dominating the entire sky. It is possible that the IBEX ribbon is created through secondary charge exchange processes. In this article we present a numerical code that calculates primary and secondary H ENA fluxes by integrating along ENA trajectories. Here we will provide descriptions of the code and preliminary results.

3D simulation of LISM oxygen flux with PUIs inside of heliosphere

During the last half decade, the structure of the heliospheric interface has attracted increasing attention with continual improvements in modelling and observations. The Interstellar Boundary Explore (IBEX) spacecraft is returning important data that require a theoretical model of Heliosphere to ensure proper interpretation. We develop a framework for understanding the measurements of heavier-than-hydrogen atoms by IBEX in terms of a 3D MHD-neutral numerical solution of the suns interaction with the interstellar medium, combined with a test particle approach for heavy atoms and ions.