This paper presents the original anisotropy that TeV cosmic rays (CRs) have in the local interstellar medium. This anisotropy is obtained using a method of flux mapping with the Liouville theorem and ...a magnetohydrodynamic (MHD) heliosphere model of the electromagnetic field to remove the particle propagation effects hidden in the measurements made by the Tibet ASγ experiment at Earth. The original interstellar anisotropy turns out to be almost a pure dipole, which results from a diffusion flow of CRs escaping along the local interstellar magnetic field into the northern Galactic halo. The observed anisotropy maps at Earth appear quite complex because the heliosphere distorts the dipole anisotropy, generating a significant amount of high-order multipoles, while interstellar magnetic field fluctuations contribute to some weak anisotropy on small angular scales. It is found that the density gradient of these CRs points approximately toward Vela in the Local Bubble, providing experimental evidence to show that the local supernova is making a special contribution to the TeV CRs we see at Earth. This special contribution will keep growing in the future tens of thousand years. The original anisotropy also reveals that the CRs spread from the source primarily along the interstellar magnetic field, while experiencing a nearly isotropic pitch-angle scattering process caused by interstellar turbulence.
The strength and orientation of the magnetic field in the nearby interstellar medium have remained elusive, despite continual improvements in observations and models. Data from NASA's Voyager mission ...and the Solar Wind ANisotropies (SWAN) experiment on board Solar and Heliospheric Observatory (SOHO) have placed observational constraints on the magnetic field, and the more recent Interstellar Boundary Explorer (IBEX) data appear to also bear an imprint of the interstellar magnetic field (ISMF). In this paper, we combine computational models of the heliosphere with data from Voyager, SOHO/SWAN, and IBEX to estimate both the strength and direction of the nearby ISMF. On the basis of our simulations, we find that a field strength of 2-3 Delta *mG pointing from ecliptic coordinates (220-224, 39-44), combined with an interstellar hydrogen density of ~0.15 cm--3, produces results most consistent with observations.
Abstract
We present a new three-dimensional, MHD-plasma/kinetic-neutrals model of the solar wind (SW) interaction with the local interstellar medium (LISM), which self-consistently includes neutral ...hydrogen and helium atoms. This new model also treats electrons as a separate fluid and includes the effect of Coulomb collisions. While the properties of electrons in the distant SW and in the LISM are mostly unknown due to the lack of in situ observations, a common assumption for any global, single-ion model is to assume that electrons have the temperature of the ion mixture, which includes pickup ions. In the new model, electrons in the SW are colder, which results in a better agreement with New Horizons observations in the supersonic SW. In the LISM, however, ions and electrons are almost in thermal equilibrium. As for the plasma mixture, the major differences between the models are in the inner heliosheath, where the new model predicts a charge-exchange-driven cooling and a decrease of the heliosheath thickness. The filtration of interstellar neutral atoms at the heliospheric interface is discussed. The new model predicts an increase in the H density by ∼2% at 1 au. However, the fraction of pristine H atoms decreases by ∼12%, while the density of atoms born in the outer and inner heliosheath increases by 5% and ∼35%, respectively. While at 1 au the density of He atoms remains unchanged, the contribution from the “warm breeze” increases by ∼3%.
The heliosphere is formed due to interaction between the solar wind (SW) and local interstellar medium (LISM). The shape and position of the heliospheric boundary, the heliopause, in space depend on ...the parameters of interacting plasma flows. The interplay between the asymmetrizing effect of the interstellar magnetic field and charge exchange between ions and neutral atoms plays an important role in the SW-LISM interaction. By performing three-dimensional, MHD plasma/kinetic neutral atom simulations, we determine the width of the outer heliosheath-the LISM plasma region affected by the presence of the heliosphere-and analyze quantitatively the distributions in front of the heliopause. It is shown that charge exchange modifies the LISM plasma to such extent that the contribution of a shock transition to the total variation of plasma parameters becomes small even if the LISM velocity exceeds the fast magnetosonic speed in the unperturbed medium. By performing adaptive mesh refinement simulations, we show that a distinct boundary layer of decreased plasma density and enhanced magnetic field should be observed on the interstellar side of the heliopause. We show that this behavior is in agreement with the plasma oscillations of increasing frequency observed by the plasma wave instrument onboard Voyager 1. We also demonstrate that Voyager observations in the inner heliosheath between the heliospheric termination shock and the heliopause are consistent with dissipation of the heliospheric magnetic field. The choice of LISM parameters in this analysis is based on the simulations that fit observations of energetic neutral atoms performed by Interstellar Boundary Explorer.
Coronal mass ejections (CMEs) are major drivers of extreme space weather conditions, as this is a matter of serious concern for our modern technologically dependent society. The development of ...numerical approaches that would simulate CME generation and propagation through the interplanetary space is an important step toward our capability to predict CME arrival times at Earth and their geoeffectiveness. In this paper, we utilize a data-constrained Gibson-Low (GL) flux rope model to generate CMEs. We derive the geometry of the initial GL flux rope using the graduated cylindrical shell method. This method uses multiple viewpoints from STEREO A and B Cor1/Cor2, and Solar and Heliospheric Observatory (SOHO)/LASCO C2/C3 coronagraphs to determine the size and orientation of a CME flux rope as it starts to erupt from the Sun. A flux rope generated in this way is inserted into a quasi-steady global magnetohydrodynamics (MHD) background solar wind flow driven by Solar Dynamics Observatory/Helioseismic and Magnetic Imager line-of-sight magnetogram data, and erupts immediately. Numerical results obtained with the Multi-Scale Fluid-Kinetic Simulation Suite (MS-FLUKSS) code are compared with STEREO and SOHO/LASCO coronagraph observations, in particular in terms of the CME speed, acceleration, and magnetic field structure.
Pickup Ions beyond the Heliopause Roytershteyn, V.; Pogorelov, N. V.; Heerikhuisen, J.
The Astrophysical journal,
08/2019, Letnik:
881, Številka:
1
Journal Article
Recenzirano
Fluxes of energetic neutral atoms (ENAs) with energies greater than 1 KeV measured by the Interstellar Boundary Explorer (IBEX) are predominantly created by charge exchange of interstellar neutral ...atoms with hot, nonthermal (pickup) ions. Since the properties of pickup ions (PUIs) depend on the place of their birth, they bear an imprint of the interaction between the solar wind (SW) and the local interstellar medium (LISM). Of special importance is a narrow "ribbon" of an enhanced ENA flux discovered by IBEX. While the origin of this ribbon is still under debate, various models attribute it to charge exchange between the LISM neutral atoms and PUIs just beyond the heliopause. In this work, we investigate the stability of PUI distributions inferred from global modeling of neutral atoms in the heliosphere using fully kinetic particle-in-cell modeling. The initial distribution consists of PUIs created from high-speed, low-temperature neutral atoms born in the supersonic SW ahead of the heliospheric termination shock (TS) and PUIs created from low-speed, high-temperature H atoms born between the TS and the heliopause. The simulations indicate that such distributions are unstable against quasi-parallel modes with fast growth timescales (of the order of one hour or less). The development of these instabilities may strongly modify the initial PUI distribution, leading, for example, to formation of a plateau in the direction parallel to the local magnetic field. These modes, however, saturate at relatively small amplitudes and do not lead to complete isotropization of the distribution on the timescales considered.
This paper summarizes the results obtained by the team “Heliosheath Processes and the Structure of the Heliopause: Modeling Energetic Particles, Cosmic Rays, and Magnetic Fields” supported by the ...International Space Science Institute (ISSI) in Bern, Switzerland. We focus on the physical processes occurring in the outer heliosphere, especially at its boundary called the heliopause, and in the local interstellar medium. The importance of magnetic field, charge exchange between neutral atoms and ions, and solar cycle on the heliopause topology and observed heliocentric distances to different heliospheric discontinuities are discussed. It is shown that time-dependent, data-driven boundary conditions are necessary to describe the heliospheric asymmetries detected by the
Voyager
spacecraft. We also discuss the structure of the heliopause, especially due to its instability and magnetic reconnection. It is demonstrated that the Rayleigh–Taylor instability of the nose of the heliopause creates consecutive layers of the interstellar and heliospheric plasma which are magnetically connected to different sources. This may be a possible explanation of abrupt changes in the galactic and anomalous cosmic ray fluxes observed by
Voyager 1
when it was crossing the heliopause structure for a period of about one month in the summer of 2012. This paper also discusses the plausibility of fitting simulation results to a number of observational data sets obtained by
in situ
and remote measurements. The distribution of magnetic field in the vicinity of the heliopause is discussed in the context of
Voyager
measurements. It is argued that a classical heliospheric current sheet formed due to the Sun’s rotation is not observed by
in situ
measurements and should not be expected to exist in numerical simulations extending to the boundary of the heliosphere. Furthermore, we discuss the transport of energetic particles in the inner and outer heliosheath, concentrating on the anisotropic spatial diffusion diffusion tensor and the pitch-angle dependence of perpendicular diffusion and demonstrate that the latter can explain the observed pitch-angle anisotropies of both the anomalous and galactic cosmic rays in the outer heliosheath.
First data from NASA's Interstellar Boundary EXplorer (IBEX) mission show a striking 'ribbon' feature of enhanced energetic neutral atom (ENA) emission. The enhancement in flux is between 2 and 3 ...times greater than adjacent regions of the sky. Yet the spectral index of ENAs appears to be the same both inside and outside the ribbon. While the ribbon itself was not predicted by any models of the heliospheric interface, its geometry appears to be related to the predicted interstellar magnetic field (ISMF) outside the heliopause (HP). In this Letter, we examine a process of ENA emission from the outer heliosheath, based on a source population of non-isotropic pick-up ions that themselves originate as ENAs from inside the HP. We find that our simplistic approach yields a ribbon of enhanced ENA fluxes as viewed from the inner heliosphere with a spatial location and ENA flux similar to the IBEX measurements, with the provision that the ions retain a partial shell distribution long enough for the ions to be neutralized. As a corollary, our idealized simulation of this mechanism suggests that ISMF is likely oriented close to the center of the observed ribbon.
Interstellar Boundary Explorer (IBEX) measurements of energetic neutral atoms (ENAs) from the heliotail show a multi-lobe structure of ENA fluxes as a function of energy between ∼0.71 and 4.29 keV. ...Below ∼2 keV, there is a single structure of enhanced ENA fluxes centered near the downwind direction. Above ∼2 keV, this structure separates into two lobes, one north and one south of the solar equatorial plane. ENA flux from these two lobes can be interpreted as originating from the fast solar wind (SW) propagating through the inner heliosheath (IHS). Alternatively, a recently published model of the heliosphere suggests that the heliotail may split into a "croissant-like" shape, and that such a geometry could be responsible for the heliotail ENA feature. Here we present results from a time-dependent simulation of the heliosphere that produces a comet-like heliotail, and show that the 11-year solar cycle leads to the formation of ENA lobes with properties remarkably similar to those observed by IBEX. The ENA energy at which the north and south lobes appear suggests that the pickup ion (PUI) temperature in the slow SW of the IHS is ∼107 K. Moreover, we demonstrate that the extinction of PUIs by charge-exchange is an essential process required to create the observed global ENA structure. While the shape and locations of the ENA lobes as a function of energy are well reproduced by PUIs that cross the termination shock, the results appear to be sensitive to the form of the distribution of PUIs injected in the IHS.
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