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G P Zank - One of the best experts on this subject based on the ideXlab platform.
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time varying heliospheric distance to the Heliopause
The Astrophysical Journal, 2017Co-Authors: Haruichi Washimi, Takashi Tanaka, G P ZankAbstract:Using a three-dimensional MHD simulation, we examine the time-varying outer heliospheric structure and distance to the Heliopause. Voyager 2 (V2) solar-wind observations show that a global merged interaction region (GMIR) with a ram-pressure of the order of several nPa normalized at 1 au enters the distant solar wind at an average rate of about one per year. This series of GMIRs adds an additional perturbative increase to the solar-wind ram-pressure in the inner heliosheath, and it also reduces the surrounding interstellar medium pressure acting on the Heliopause; consequently, our simulation results in the distance to the Heliopause being ~14 au larger when compared to the case when a series of GMIRs is not taken into account. In addition, OMNI data show that the solar-wind ram-pressure near the Earth increases from ~1.3 nPA in 2010 and before to 1.7–2.4 nPa after that until the present time. These variations in the overall ram-pressure of the solar wind are also included in our simulation. The inclusion of the time variable solar-wind ram-pressure and the series of GMIRs allows us to illustrate how the realistic distance to the Heliopause varies in response to both long- and short time variability in solar activity. This simulation study also explains the puzzle of why V2 has not yet crossed the Heliopause, although it is now almost 5 years since Voyager 1 crossed the Heliopause in 2012.
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mhd modeling of the outer heliospheric structures around the Heliopause
The Astrophysical Journal, 2015Co-Authors: Haruichi Washimi, G P Zank, Takashi Tanaka, K MunakataAbstract:Voyager 1 (V1) observed the first step increase of the galactic cosmic ray (GCR) flux for energies >70 MeV and >211 MeV near the Heliopause at 2012.31, just before the magnetic field polarity changed from "away" to "toward" at 2012.47. This event was not accompanied by an anomalous cosmic ray (ACR) flux change. The second GCR step increase, together with an ACR decrease, was observed at 2012.65. The magnetic field change was observed with its polarity changing from a "toward" to an apparent "away" direction at 2012.56, at ~122 AU from the Sun, with an eventual orientation of 22°. The later magnetic field has been identified as the interstellar magnetic field and the current sheet at the polarity change is identified as the boundary of the interstellar magnetic field. We present a three-dimensional stationary MHD simulation with a Heliopause located at ~122 AU and a magnetic field polarity change across the Heliopause. The apparent "away" polarity of the magnetic field is confirmed to be that of the interstellar magnetic field in this simulation. We present a detailed analysis of the magnetic field line topology in the vicinity of the Heliopause and argue for a favorable condition of the first GCR step increase with no concurrent ACR flux change before the time corresponding to the magnetic polarity change at 2012.47.
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instability of the Heliopause
Journal of Physics: Conference Series, 2015Co-Authors: G P Zank, K Avinash, B Dasgupta, Shikha BhadoriaAbstract:The Heliopause (HP) separates the tenuous hot heliosheath plasma from the relatively dense cool magnetized plasma of the local interstellar medium (LISM). Fluid acceleration in the HP region can therefore drive Rayleigh-Taylor-like and Kelvin-Helmholtz- like instabilities. Charge exchange coupling of plasma ions and primary interstellar neutral atoms provides an effective gravity, suggesting the possibility of Rayleigh Taylor-like (RT-like) instabilities. Shear flow due to the velocity difference between the heliosheath and the interstellar flows drives Kelvin Helmholtz-like (KH-like) modes on the Heliopause. Magnetic fields damp the classical KH instability. However, we show that energetic neutral atoms (ENAs) destabilize KH-modes,even in the presence of interplanetary and interstellar magnetic fields. We consider a model that includes a number of effects that are important in the heliosphere such as resonant change exchange between the primary neutrals and the solar wind plasma, ENAs from the inner heliosheath, plasma flows along the Heliopause and magnetic fields in the inner and outer heliosheath. We find that the nose region is unstable to RT-like modes for HP parameters, while the shoulder region is unstable to a new instability that has the characteristics of a mixed RT-KH-like mode. These instabilities are not stabilized by typical values of the magnetic fields in the inner and outer heliosheath close to the nose and shoulder regions. Whereas ENAs have a stabilizing influence on the RT instability in the vicinity of the nose region (due to counter streaming), they have a destabilizing influence on the KH instability in the vicinity of the flanks. We find that even in the presence of interplanetary and interstellar magnetic fields, ENAs can drive a new form of KH-like instability on the flanks. An analysis of the collisional and anomalous magnetic field diffusion time scales shows that ideal MHD is an appropriate model at the HP. The interstellar magnetic field therefore drapes over the HP and does not diffuse into the inner heliosheath (IHS). However, RT-like, RT-KH-like, and KH-like instabilities serve to drag outer heliosheath (OHS)/interstellar magnetic field into the IHS, allowing for local reconnection of interplanetary and interstellar magnetic field. Such reconnection may 1) enhance the mixing of plasmas across the Heliopause, and 2) provide open magnetic field lines that allow easy ingress of galactic cosmic rays into the heliosphere and easy loss of anomalous cosmic rays.
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instability of the Heliopause driven by charge exchange interactions
The Astrophysical Journal, 2014Co-Authors: G P Zank, K Avinash, B Dasgupta, Shikha BhadoriaAbstract:The stability of the Heliopause that separates the tenuous hot magnetized heliosheath plasma from the dense cool local interstellar magnetized plasma is examined using a fully general model that includes all the essential physical processes. Charge exchange coupling between plasma protons and primary interstellar neutral atoms provides an effective gravity that drives Rayleigh-Taylor (RT)-like instabilities. The velocity difference or shear between the heliosheath and interstellar flows, when coupled to energetic neutral atoms (ENAs), drives a Kelvin-Helmholtz (KH)-like instability on the Heliopause. The shoulder region of the Heliopause is unstable to a new instability that has characteristics of a mixed RT-KH-like mode. The instabilities are not stabilized by typical values of the magnetic fields in the inner and outer heliosheath (OHS). ENAs play an essential role in driving the KH-like instability, which is fully stabilized in their absence by magnetic fields. The nonlinear phase of these instabilities is briefly discussed. We also discuss the possibility that RT-like or mixed KH-RT-like instabilities drag outer heliosheath/very local interstellar medium (OHS/VLISM) magnetic field lines into the inner heliosheath (IHS) with the VLISM flow, and the possibility that IHS and VLISM magnetic field lines experience reconnection. Such reconnection may (1) greatly enhance the mixing ofmore » plasmas across the Heliopause and (2) provide open magnetic field lines that allow easy ingress of galactic cosmic rays into the heliosphere and corresponding easy loss of anomalous cosmic rays from the heliosphere.« less
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interstellar boundary explorer measurements and magnetic field in the vicinity of the Heliopause
The Astrophysical Journal, 2011Co-Authors: N V Pogorelov, D. J. Mccomas, G P Zank, J Heerikhuisen, S N Borovikov, Priscilla C FrischAbstract:The combination of the Interstellar Boundary Explorer (IBEX) all-sky maps of the energetic neutral atom (ENA) fluxes with the Voyager in situ measurements provides a unique opportunity to learn about the physics governing the solar wind interaction with the local interstellar medium. The first IBEX results revealed a sky-spanning "ribbon" of unexpectedly intense emissions of ENAs that had not been predicted previously by any physical model. A number of explanations were proposed to explain the IBEX ribbon, some of them associated with the distribution of the interstellar magnetic field (ISMF) coupled with the interplanetary magnetic field at the Heliopause. The position of the ribbon in the sky correlates with the line-of-sight directions perpendicular to the modeled ISMF. In this paper, we analyze such distributions for a variety of ISMF strengths and directions in order to reveal the topology of the surface that may potentially contain the ENA sources creating the ribbon. We also analyze the distributions of total pressure exerted on the Heliopause as a result of its draping by the ISMF. The effects of solar cycle variations on the ribbon topology are discussed.
N V Pogorelov - One of the best experts on this subject based on the ideXlab platform.
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Heliosheath Processes and the Structure of the Heliopause: Modeling Energetic Particles, Cosmic Rays, and Magnetic Fields
Space Science Reviews, 2017Co-Authors: N V Pogorelov, E. C. Stone, M S Potgieter, H. Fichtner, A. Czechowski, A. Lazarian, B. Lembege, J. A. Roux, K. Scherer, R D StraussAbstract: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.
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three dimensional features of the outer heliosphere due to coupling between the interstellar and heliospheric magnetic field v the bow wave heliospheric boundary layer instabilities and magnetic reconnection
The Astrophysical Journal, 2017Co-Authors: N V Pogorelov, D. A. Gurnett, J Heerikhuisen, L. F. Burlaga, V Roytershteyn, W S KurthAbstract: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 IBEX.
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transient shocks beyond the Heliopause
Journal of Physics: Conference Series, 2015Co-Authors: R L Fermo, N V Pogorelov, L. F. BurlagaAbstract:The Heliopause is a rich, dynamic surface affected by the time-dependent solar wind. Stream interactions due to coronal mass ejections (CMEs), corotating interaction regions (CIRs), and other transient phenomena are known to merge producing global merged interaction regions (GMIRs). Numerical simulations of the solar wind interaction with the local interstellar medium (LISM) show that GMIRs, as well other time-dependent structures in the solar wind, may produce compression/rarefaction waves and shocks in the LISM behind the Heliopause. These shocks may initiate wave activity observed by the Voyager spacecraft. The magnetometer onboard Voyager 1 indeed observed a few structures that may be interpreted as shocks. We present numerical simulations of such shocks in the year of 2000, when both Voyager spacecraft were in the supersonic solar wind region, and in 2012, when Voyager 1 observed traveling shocks. In the former case, Voyager observations themselves provide time- dependent boundary conditions in the solar wind. In the latter case, we use OMNI data at 1 AU to analyze the plasma and magnetic field behavior after Voyager 1 crossed the heliospheric boundary. Numerical results are compared with spacecraft observations.
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voyager 1 near the Heliopause
The Astrophysical Journal, 2014Co-Authors: S N Borovikov, N V PogorelovAbstract:Recent observations from the Voyager 1 spacecraft show that it is sampling the local interstellar medium (LISM). This is quite surprising because no realistic, steady-state model of the solar wind (SW) interaction with the LISM gives an inner heliosheath width as narrow as ~30 AU. This includes models that assume a strong redistribution of the ion energy to the tails in the pickup ion distribution function. We show that the Heliopause (HP), which separates the SW from the LISM, is not a smooth tangential discontinuity, but rather a surface subject to Rayleigh-Taylor-type instabilities which can result in LISM material penetration deep inside the SW. We also show that the HP flanks are always subject to a Kelvin-Helmholtz instability. The instabilities are considerably suppressed near the HP nose by the heliospheric magnetic field in steady-state models, but reveal themselves in the presence of solar cycle effects. We argue that Voyager 1 may be in one such instability region and is therefore observing plasma densities much higher than those in the pristine SW. These results may explain the early penetration of Voyager 1 into the LISM. They also show that there is a possibility that the spacecraft may start sampling the SW again before it finally leaves the heliosphere.
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interstellar boundary explorer measurements and magnetic field in the vicinity of the Heliopause
The Astrophysical Journal, 2011Co-Authors: N V Pogorelov, D. J. Mccomas, G P Zank, J Heerikhuisen, S N Borovikov, Priscilla C FrischAbstract:The combination of the Interstellar Boundary Explorer (IBEX) all-sky maps of the energetic neutral atom (ENA) fluxes with the Voyager in situ measurements provides a unique opportunity to learn about the physics governing the solar wind interaction with the local interstellar medium. The first IBEX results revealed a sky-spanning "ribbon" of unexpectedly intense emissions of ENAs that had not been predicted previously by any physical model. A number of explanations were proposed to explain the IBEX ribbon, some of them associated with the distribution of the interstellar magnetic field (ISMF) coupled with the interplanetary magnetic field at the Heliopause. The position of the ribbon in the sky correlates with the line-of-sight directions perpendicular to the modeled ISMF. In this paper, we analyze such distributions for a variety of ISMF strengths and directions in order to reveal the topology of the surface that may potentially contain the ENA sources creating the ribbon. We also analyze the distributions of total pressure exerted on the Heliopause as a result of its draping by the ISMF. The effects of solar cycle variations on the ribbon topology are discussed.
D. J. Mccomas - One of the best experts on this subject based on the ideXlab platform.
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slowdown and heating of interstellar neutral helium by elastic collisions beyond the Heliopause
arXiv: Solar and Stellar Astrophysics, 2021Co-Authors: Pawel Swaczyna, D. J. Mccomas, Eric Zirnstein, F Rahmanifard, J HeerikhuisenAbstract:Direct sampling of interstellar neutral (ISN) atoms close to the Sun enables studies of the very local interstellar medium (VLISM) around the heliosphere. The primary population of ISN helium atoms has, until now, been assumed to reflect the pristine VLISM conditions at the Heliopause. Consequently, the atoms observed at 1 au by the Interstellar Boundary Explorer (IBEX) were used to determine the VLISM temperature and velocity relative to the Sun, without accounting for elastic collisions with other species outside the Heliopause. Here, we evaluate the effect of these collisions on the primary ISN helium population. We follow trajectories of helium atoms and track their collisions with slowed plasma and interstellar hydrogen atoms ahead of the Heliopause. Atoms typically collide a few times in the outer heliosheath, and only ~1.5% of the atoms are not scattered at all. We use calculated differential cross sections to randomly choose scattering angles in these collisions. We estimate that the resulting primary ISN helium atoms at the Heliopause are slowed down by ~0.45 km/s and heated by ~1100 K compared to the pristine VLISM. The resulting velocity distribution is asymmetric and shows an extended tail in the antisunward direction. Accounting for this change in the parameters derived from IBEX observations gives the Sun's relative speed of 25.85 km/s and temperature of 6400 K in the pristine VLISM. Finally, this paper serves as a source of the differential cross sections for elastic collisions with helium atoms.
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the characterization of secondary interstellar neutral oxygen beyond the Heliopause a detailed analysis of the ibex lo oxygen observations
The Astrophysical Journal, 2019Co-Authors: J. Park, N A Schwadron, A. Szabo, S A Fuselier, H Kucharek, N Paschalidis, D Heirtzler, E Mobius, D. J. MccomasAbstract:In this study, we analyze the directional distribution of the secondary interstellar neutral (ISN) O population observed by the IBEX-Lo neutral atom camera on the Interstellar Boundary EXplorer (IBEX) via the comparison with simulated ISN O intensity maps produced by an analytical model. In the analytical model, we assume that there are primary and secondary ISN populations at the Heliopause. We further assume that each population is represented by a Maxwellian velocity distribution function with its own flow parameters. For the viewing directions of IBEX-Lo, we compute the incoming atom speeds at the Heliopause with a Keplerian equation of motion in the solar gravity field. Then, we calculate analytically the distribution function to obtain the ISN intensities at Earth’s orbit. We compare the simulated O intensity maps with the IBEX-Lo O sky map to determine the most likely flow parameters of the secondary ISN O population. Using this method, we find the most likely flow parameters of the secondary ISN O population: V(sub SecISNO) = 11 ± 2.2 km s(exp -1), λ(sub SecISNO) = 67° ± 1°.5, β(sub SecISNO) = -12° ± 1°.6, and T(sub SecISNO) = 10,000 ± 1500 K. The results indicate that the secondary ISN O flow direction is deflected toward lower ecliptic longitude and higher negative ecliptic latitude from the ISN gas flow direction at the Heliopause. The secondary ISN O flow direction is more deflected from the ISN gas flow direction than the secondary ISN He flow direction.
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galactic cosmic ray anisotropies voyager 1 in the local interstellar medium
arXiv: Space Physics, 2019Co-Authors: A. C. Cummings, Nand Lal, E. C. Stone, D. J. Mccomas, J. S. Rankin, B C HeikkilaAbstract:Since crossing the Heliopause on August 25, 2012, Voyager 1 observed reductions in galactic cosmic ray count rates caused by a time-varying depletion of particles with pitch angles near 90-deg, while intensities of particles with other pitch angles remain unchanged. Between late 2012 and mid-2017, three large-scale events occurred, lasting from ~100 to ~630 days. Omnidirectional and directional high-energy data from Voyager 1's Cosmic Ray Subsystem are used to report cosmic ray intensity variations. Omnidirectional (greater than ~20 MeV) proton-dominated measurements show up to a 3.8% intensity reduction. Bi-directional (greater than ~70 MeV) proton-dominated measurements taken from various spacecraft orientations provide insight about the depletion region's spatial properties. We characterize the anisotropy as a "notch" in an otherwise uniform pitch-angle distribution of varying depth and width centered about 90 degrees in pitch angle space. The notch averages 22-deg wide and 15% deep - signifying a depletion region that is broad and shallow. There are indications that the anisotropy is formed by a combination of magnetic trapping and cooling downstream of solar-induced transient disturbances in a region that is also likely influenced by the highly compressed fields near the Heliopause.
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strong scattering of kev pickup ions in the local interstellar magnetic field draped around our heliosphere implications for the ibex ribbon s source and imap
The Astrophysical Journal, 2019Co-Authors: Eric Zirnstein, D. J. Mccomas, N A Schwadron, Maher A. Dayeh, J Heerikhuisen, Pawel SwaczynaAbstract:The leading hypothesis for the origin of the Interstellar Boundary Explorer (IBEX) "ribbon" of enhanced energetic neutral atoms (ENAs) from the outer heliosphere is the secondary ENA mechanism, whereby neutralized solar wind ions escape the heliosphere and, after several charge-exchange processes, may propagate back toward Earth primarily in directions perpendicular to the local interstellar magnetic field (ISMF). However, the physical processes governing the parent protons outside of the Heliopause are still unconstrained. In this study, we compute the "spatial retention" model proposed by Schwadron & McComas (2013) in a 3D simulated heliosphere. In their model, pickup ions outside the Heliopause that originate from the neutral solar wind are spatially-retained in a region of space via strong pitch angle scattering before becoming ENAs. We find that the ribbon's intensity and shape can vary greatly depending on the pitch angle scattering rate both inside and outside the spatial retention region, potentially contributing to the globally distributed flux. The draping of the ISMF around the Heliopause creates an asymmetry in the average distance to the ribbon's source as well as an asymmetry in the ribbon's shape, i.e., radial cross section of ENA flux through the circular ribbon. The spatial retention model adds an additional asymmetry to the ribbon's shape due to the enhancement of ions in the retention region close to the Heliopause. Finally, we demonstrate how the ribbon's structure observed at 1 au is affected by different instrument capabilities, and how the Interstellar Mapping and Acceleration Probe (IMAP) may observe the ribbon.
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galactic cosmic ray anisotropies voyager 1 in the local interstellar medium
The Astrophysical Journal, 2019Co-Authors: A. C. Cummings, Nand Lal, E. C. Stone, D. J. Mccomas, J. S. Rankin, B C HeikkilaAbstract:Since crossing the Heliopause on 2012 August 25, Voyager 1 observed reductions in galactic cosmic ray count rates caused by a time-varying depletion of particles with pitch angles near 90?, while intensities of particles with other pitch angles remain unchanged. Between late 2012 and mid-2017, three large-scale events occurred, lasting from ~100 to ~630 days. Omnidirectional and directional high-energy data from Voyager 1's Cosmic Ray Subsystem are used to report cosmic ray intensity variations. Omnidirectional (20 MeV) proton-dominated measurements show up to a 3.8% intensity reduction. Bidirectional (70 MeV) proton-dominated measurements taken from various spacecraft orientations provide insight about the depletion region's spatial properties. We characterize the anisotropy as a "notch" in an otherwise uniform pitch angle distribution of varying depth and width centered about 90? in pitch angle space. The notch averages 22? wide and 15% deep, signifying a depletion region that is broad and shallow. There are indications that the anisotropy is formed by a combination of magnetic trapping and cooling downstream of solar-induced transient disturbances in a region that is also likely influenced by the highly compressed fields near the Heliopause.
N A Schwadron - One of the best experts on this subject based on the ideXlab platform.
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Heliosheath Properties Measured from a Voyager 2 to Voyager 1 Transient
The Astrophysical Journal, 2019Co-Authors: J. S. Rankin, David J. Mccomas, John D. Richardson, N A SchwadronAbstract:In mid-2012, a GMIR observed by Voyager 2 crossed through the heliosheath and collided with the Heliopause, generating a pressure pulse that propagated into the very local interstellar medium. The effects of the transmitted wave were seen by Voyager 1 just 93 days after its own Heliopause crossing. The passage of the transient was accompanied by long-lasting decreases in galactic cosmic ray intensities that occurred from ~2012.55 to ~2013.35 and ~2012.91 to ~2013.70 at Voyager 2 and Voyager 1, respectively. Omnidirectional (>20 MeV) proton-dominated measurements from each spacecraft's Cosmic Ray Subsystem reveal a remarkable similarity between these causally-related events, with a correlation coefficient of 91.2% and a time-lag of 130 days. Knowing the locations of the two spacecraft, we use the observed time-delay to calculate the GMIR's average speed through the heliosheath (inside the Heliopause) as a function of temperature in the very local interstellar medium. This, combined with particle, field, and plasma observations enables us to infer previously unmeasured properties of the heliosheath, including a range of sound speeds and total effective pressures. For a nominal temperature of ~20,000 K just outside the Heliopause, we find a sound speed of 314 (+/-) 32 km/s and total effective pressure of 267 (+/-) 55 fPa inside the Heliopause. We compare these results with the Interstellar Boundary Explorer's data-driven models of heliosheath pressures derived from energetic neutral atom fluxes (the globally distributed flux) and present them as additional evidence that the heliosheath's dynamics are driven by suprathermal energetic processes.
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the characterization of secondary interstellar neutral oxygen beyond the Heliopause a detailed analysis of the ibex lo oxygen observations
The Astrophysical Journal, 2019Co-Authors: J. Park, N A Schwadron, A. Szabo, S A Fuselier, H Kucharek, N Paschalidis, D Heirtzler, E Mobius, D. J. MccomasAbstract:In this study, we analyze the directional distribution of the secondary interstellar neutral (ISN) O population observed by the IBEX-Lo neutral atom camera on the Interstellar Boundary EXplorer (IBEX) via the comparison with simulated ISN O intensity maps produced by an analytical model. In the analytical model, we assume that there are primary and secondary ISN populations at the Heliopause. We further assume that each population is represented by a Maxwellian velocity distribution function with its own flow parameters. For the viewing directions of IBEX-Lo, we compute the incoming atom speeds at the Heliopause with a Keplerian equation of motion in the solar gravity field. Then, we calculate analytically the distribution function to obtain the ISN intensities at Earth’s orbit. We compare the simulated O intensity maps with the IBEX-Lo O sky map to determine the most likely flow parameters of the secondary ISN O population. Using this method, we find the most likely flow parameters of the secondary ISN O population: V(sub SecISNO) = 11 ± 2.2 km s(exp -1), λ(sub SecISNO) = 67° ± 1°.5, β(sub SecISNO) = -12° ± 1°.6, and T(sub SecISNO) = 10,000 ± 1500 K. The results indicate that the secondary ISN O flow direction is deflected toward lower ecliptic longitude and higher negative ecliptic latitude from the ISN gas flow direction at the Heliopause. The secondary ISN O flow direction is more deflected from the ISN gas flow direction than the secondary ISN He flow direction.
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strong scattering of kev pickup ions in the local interstellar magnetic field draped around our heliosphere implications for the ibex ribbon s source and imap
The Astrophysical Journal, 2019Co-Authors: Eric Zirnstein, D. J. Mccomas, N A Schwadron, Maher A. Dayeh, J Heerikhuisen, Pawel SwaczynaAbstract:The leading hypothesis for the origin of the Interstellar Boundary Explorer (IBEX) "ribbon" of enhanced energetic neutral atoms (ENAs) from the outer heliosphere is the secondary ENA mechanism, whereby neutralized solar wind ions escape the heliosphere and, after several charge-exchange processes, may propagate back toward Earth primarily in directions perpendicular to the local interstellar magnetic field (ISMF). However, the physical processes governing the parent protons outside of the Heliopause are still unconstrained. In this study, we compute the "spatial retention" model proposed by Schwadron & McComas (2013) in a 3D simulated heliosphere. In their model, pickup ions outside the Heliopause that originate from the neutral solar wind are spatially-retained in a region of space via strong pitch angle scattering before becoming ENAs. We find that the ribbon's intensity and shape can vary greatly depending on the pitch angle scattering rate both inside and outside the spatial retention region, potentially contributing to the globally distributed flux. The draping of the ISMF around the Heliopause creates an asymmetry in the average distance to the ribbon's source as well as an asymmetry in the ribbon's shape, i.e., radial cross section of ENA flux through the circular ribbon. The spatial retention model adds an additional asymmetry to the ribbon's shape due to the enhancement of ions in the retention region close to the Heliopause. Finally, we demonstrate how the ribbon's structure observed at 1 au is affected by different instrument capabilities, and how the Interstellar Mapping and Acceleration Probe (IMAP) may observe the ribbon.
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scatter free pickup ions beyond the Heliopause as a model for the interstellar boundary explorer ribbon
The Astrophysical Journal, 2010Co-Authors: S V Chalov, Vladislav V. Izmodenov, Dmitry Alexashov, D. J. Mccomas, N A Schwadron, Yury G MalamaAbstract:We present a new kinetic-gasdynamic model of the solar wind interaction with the local interstellar medium. The model incorporates several processes suggested earlier for the origin of the ribbon?the most prominent feature seen in the all-sky maps of heliospheric energetic neutral atoms (ENAs) discovered by the Interstellar Boundary Explorer (IBEX). The ribbon is a region of enhanced fluxes of ENAs crossing almost the entire sky. Soon after the ribbon's discovery, it was realized that the enhancement of the fluxes could be in the directions where the radial component of the interstellar magnetic field around the Heliopause is close to zero. Our model includes secondary charge exchange of the interstellar H atoms with the interstellar pickup protons outside the Heliopause. Previously, in the frame of a kinetic-gasdynamic model where pickup protons are treated as a separate kinetic component, it was shown that the interstellar pickup protons outside the Heliopause may be a significant source of ENAs at energies above 1 keV. The key difference between the current work and the previous models is in the assumption of no pitch-angle scattering for newly created pickup protons outside the Heliopause. We demonstrate that in the limit of no pitch-angle scattering ribbon of enhanced ENA fluxes appears in the model, and this may qualitatively explain the ribbon discovered by IBEX.
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scatter free pickup ions beyond the Heliopause as a model for the interstellar boundary explorer ibex ribbon
arXiv: Solar and Stellar Astrophysics, 2010Co-Authors: S V Chalov, Vladislav V. Izmodenov, Dmitry Alexashov, D. J. Mccomas, Yury G Malama, N A SchwadronAbstract:We present new kinetic-gasdynamic model of the solar wind interaction with the local interstellar medium. The model incorporates several processes suggested by McComas et al. (2009) for the origin of the heliospheric ENA ribbon -- the most prominent feature seen in the all sky maps of heliospheric ENAs discovered by the Interstellar Boundary Explorer (IBEX). The ribbon is a region of enhanced fluxes of ENAs crossing almost the entire sky. Soon after the ribbon's discovery it was realized (McComas et al., 2009) that the enhancement of the fluxes could be in the directions where the radial component of the interstellar magnetic field around the Heliopause is close to zero (Schwadron et al., 2009). Our model includes secondary charge exchange of the interstellar H atoms with the interstellar pickup protons outside the Heliopause and is a further advancement of the kinetic-gasdynamic model by Malama et al. (2006) where pickup protons were treated as a separate kinetic component. Izmodenov et al. (2009) have shown in the frame of Malama's model that the interstellar pickup protons outside the Heliopause maybe a significant source of ENAs at energies above 1 keV. The difference between the current work and that of Izmodenov et al. (2009) is in the assumption of no-scattering for newly created pickup protons outside the Heliopause. In this limit the model produces a feature qualitatively similar to the ribbon observed by IBEX.
V Florinski - One of the best experts on this subject based on the ideXlab platform.
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galactic cosmic ray modulation near the Heliopause
The Astrophysical Journal, 2014Co-Authors: Xiaocheng Guo, V FlorinskiAbstract:We investigate the modulation of galactic cosmic rays in the inner and outer heliosheaths using three-dimensional numerical simulations. The model is based on the Parker transport equation integrated using a stochastic phase-space trajectory method. Integration is performed on a plasma background obtained from a global three-dimensional magnetohydrodynamic simulations. Our results predict a negligible amount of modulation in the outer heliosheath because of weak scattering of cosmic ray ions owing to very low levels of magnetic fluctuation power at wavenumbers relevant to the transport of cosmic rays with MeV to GeV energies. This means that the Heliopause may be treated as a Dirichlet-type boundary for the purpose of energetic particle modeling. We present models with and without drift velocity to facilitate comparison with papers published earlier. We also attempt to reproduce the sudden step-like increases of cosmic-ray intensity observed by Voyager 1 before its encounter with the Heliopause. Our results indicate that very slow cross-field diffusion in the outer heliosheath could produce a large gradient of cosmic rays inside the heliospheric boundary. The resulting large gradient in cosmic-ray intensity near the Heliopause qualitatively agrees with recent Voyager 1 observations.
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termination shock asymmetries as seen by the voyager spacecraft the role of the interstellar magnetic field and neutral hydrogen
The Astrophysical Journal, 2007Co-Authors: Nikolai V. Pogorelov, E. C. Stone, V Florinski, G P ZankAbstract:We show that asymmetries of the termination shock due to the influence of the interstellar magnetic field (ISMF) are considerably smaller in the presence of neutral hydrogen atoms, which tend to symmetrize the Heliopause, the termination shock, and the bow shock due to charge exchange with charged particles. This leads to a much stronger restriction on the ISMF direction and its strength. We demonstrate that in the presence of the interplanetary magnetic field the plane defined by the local interstellar medium (LISM) velocity and magnetic field vectors does not exactly coincide with the plane defined by the interstellar neutral helium and hydrogen velocity vectors in the supersonic solar wind region, which limits the accuracy of the inferred direction of the ISMF. We take into account the tilt of the LISM velocity vector with respect to the ecliptic plane and show that magnetic fields as strong as 3 μG or greater may be necessary to account for the observed asymmetry. Estimates are made of the longitudinal streaming anisotropy of energetic charged particles at the termination shock caused by the nonalignment of the interplanetary magnetic field with its surface. By investigating the behavior of interplanetary magnetic field lines that cross the Voyager 1 trajectory in the inner heliosheath, we estimate the length of the trajectory segment that is directly connected by these lines to the termination shock. A possible effect of the ISMF draping over the Heliopause is discussed in connection with radio emission generated in the outer heliosheath.
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Termination Shock Asymmetries as Seen by the Voyager Spacecraft: The Role of the Interstellar Magnetic Field and Neutral Hydrogen
The Astrophysical Journal, 2007Co-Authors: Nikolai V. Pogorelov, E. C. Stone, V Florinski, G P ZankAbstract:We show that asymmetries of the termination shock due to the influence of the interstellar magnetic field (ISMF) are considerably smaller in the presence of neutral hydrogen atoms, which tend to symmetrize the Heliopause, the termination shock, and the bow shock due to charge exchange with charged particles. This leads to a much stronger restriction on the ISMF direction and its strength. We demonstrate that in the presence of the interplanetary magnetic field the plane defined by the local interstellar medium (LISM) velocity and magnetic field vectors does not exactly coincide with the plane defined by the interstellar neutral helium and hydrogen velocity vectors in the supersonic solar wind region, which limits the accuracy of the inferred direction of the ISMF. We take into account the tilt of the LISM velocity vector with respect to the ecliptic plane and show that magnetic fields as strong as 3 μG or greater may be necessary to account for the observed asymmetry. Estimates are made of the longitudinal streaming anisotropy of energetic charged particles at the termination shock caused by the nonalignment of the interplanetary magnetic field with its surface. By investigating the behavior of interplanetary magnetic field lines that cross the Voyager 1 trajectory in the inner heliosheath, we estimate the length of the trajectory segment that is directly connected by these lines to the termination shock. A possible effect of the ISMF draping over the Heliopause is discussed in connection with radio emission generated in the outer heliosheath.
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mhd instabilities at the Heliopause
PHYSICS OF THE INNER HELIOSHEATH: Voyager Observations Theory and Future Prospects; 5th Annual IGPP International Astrophysics Conference, 2006Co-Authors: B Dasgupta, V Florinski, J Heerikhuisen, G P ZankAbstract:The Heliopause (HP) is the outer edge of the heliosphere which separates the tenuous and hot heliosheath plasma on one side and the relatively dense and cool magnetized interstellar plasma on the other side. As a surface of tangential discontinuity, the HP is subjected to both Rayleigh‐Taylor (RT) and Kelvin‐Helmholtz (KH) instabilities. The coupling between plasma ions and neutral atoms through the process of charge exchange provides an “effective gravity” at the HP, while a shear flow exists across it. We derive analytically the linearized dispersion relation for waves propagating along the surface of this discontinuity, which represents a combined RT/KH analysis. We investigate both the purely hydrodynamic, as well as magnetohydrodynamic, cases, and find that interstellar and heliospheric magnetic fields can help stabilize the HP for RT and KH‐type instabilities.
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Heliopause stability in the presence of neutral atoms rayleigh taylor dispersion analysis and axisymmetric mhd simulations
Journal of Geophysical Research, 2005Co-Authors: V Florinski, G P Zank, N V PogorelovAbstract:[1] The Heliopause, a surface separating the tenuous hot heliosheath flow and the dense, magnetized interstellar flow, is subject to instabilities of the Rayleigh-Taylor and Kelvin-Helmholtz types. The dynamic properties of this discontinuity is of considerable importance for understanding the neutral atom and cosmic ray filtration at the interface. Here we investigate the stability of the upwind segment of the Heliopause in the presence of charge exchange collisions using both an analytic (dispersion relation) approach and a numerical model that includes the interstellar magnetic field. Linear analysis yields dispersion relations that admit imaginary solutions for a range of wave numbers, implying that the stagnation point on the Heliopause is Rayleigh-Taylor unstable to small perturbations propagating parallel to the discontinuity surface. Effects of interstellar and heliosheath atoms are analyzed separately. We confirm our analytic results by performing time-dependent numerical simulations of the nonlinear development of this instability using a multifluid MHD-neutral approach. For typical solar wind and LISM conditions we obtain cyclical evolution of the upwind Heliopause with a period of about 100 years. The amplitude of these oscillations is found to be dependent on the presence of hot heliosheath neutrals. We discuss the effect of a strong LISM magnetic field on the Heliopause stability and possible implications of the obtained instability on the X-ray emission and cosmic ray transport in the outer heliosphere.