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G. P. Zank - One of the best experts on this subject based on the ideXlab platform.
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Mediation of the heliospheric Termination Shock by Termination‐Shock‐accelerated particles
2010Co-Authors: V. Florinski, Robert B. Decker, G. P. ZankAbstract:Energetic particle measurements made by Voyager 2 during its crossing of the heliospheric Termination Shock had distinctive features of a locally Shock‐accelerated component in the energy range between 1 and 3.5 MeV. Intensities of energetic ions rose exponentially upstream of the Shock and were accompanied by a deceleration of the bulk plasma flow. Our analysis of the Voyager 2 Shock precursor shows that the Termination Shock was in a rare state known as a cosmic‐ray‐mediated Shock, where plasma slowdown in the precursor is produced by a positive energetic particle radial pressure gradient. The amount of deceleration in the last 40 days of the precursor was about 13% (by dynamic pressure), which is consistent with earlier model predictions. However, the precursor was narrower than predicted by these models, which assumed dominance of a high‐energy anomalous cosmic‐ray component.
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Micro‐Structure of the Heliospheric Termination Shock
AIP Conference Proceedings, 2009Co-Authors: G. P. Zank, R. H. Burrows, M. Oka, B. Dasgupta, Jacob Heerikhuisen, G. M. WebbAbstract:Observations by the Voyager 2 spacecraft of the structure of the heliospheric Termination Shock revealed a quasi‐perpendicular structure that possessed many of the characteristics that are familiar to us from perpendicular Shocks observed in the inner heliosphere. However, a surprise was the relative lack of heating experienced by thermal solar wind ions (and electrons), leading to the suggestion that the pickup ions were primarily heated at the heliospheric Termination Shock. Because the Voyager plasma instrument cannot measure the interstellar pickup ions directly, their behavior at the Termination Shock could not be gauged directly. Nonetheless, it had already been predicted [16] that the primary dissipation mechanism for the quasi‐perpendicular Termination Shock would be the reflection of pickup ions rather than solar wind ions; this because of the shell‐like structure of the pickup ion distribution function. We discuss the effect of pickup ions including their trajectories within the structure of the Shock observed by Voyager 2. A model for the Shock structure is constructed on the basis of preferentially reflected pickup ions, solutions are discussed, and we estimate the degree of heating for the various components.
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Termination Shock Surfing
AIP Conference Proceedings, 2009Co-Authors: R. H. Burrows, G. P. Zank, G. M. WebbAbstract:The recent Voyager 2 (V2) observations of the Termination Shock (TS) indicate that it is a plasma Shock like no other in the heliosphere with dynamics and structure heavily influenced by the presence of an energized population of pickup ions (PUIs). The ‘unexpected’ finding of a cold plasma in the heliosheath with very little heating of the solar wind suggests that the energy dissipated by the Shock could be dominated by the acceleration of PUIs at the TS. We examine the ’Shock surfing’ mechanism at the test particle level, where multiply reflected ions (MRIs) gain energy from the motional electric field as a consequence of reflection from the cross‐Shockpotential, for a specific model of the TS3 (the third TS crossing measured by V2). The energization of PUI shell distributions at a stationary, perpendicular model of the TS3 indicate that Shock surfing can provide substantial PUI acceleration and a dissipation mechanism at the TS. For a strong enough cross‐Shock potential and sufficiently narrow Shock ra...
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Heliospheric Termination Shock strength from a multi‐fluid model
AIP Conference Proceedings, 2008Co-Authors: Hans‐r. Müller, Laura M. Woodman, G. P. ZankAbstract:A suite of 64 global heliospheric models, for which the interstellar densities and temperatures are varied within reasonable bounds, is analyzed with respect to the location of the Termination Shock on and off the stagnation axis, its temperature, and its compression ratio. The empirical relations regarding the Termination Shock, the heliopause and the interstellar bow Shock, are discussed, as are the physical reasons behind these relations.
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A FOCUSED TRANSPORT APPROACH TO PICKUP ION Shock ACCELERATION: IMPLICATIONS FOR THE Termination Shock
The Astrophysical Journal, 2007Co-Authors: J. A. Le Roux, G. M. Webb, Vladimir Florinski, G. P. ZankAbstract:The discovery of low-energy suprathermal ions coming directly from the solar wind Termination Shock by the Voyager 1 spacecraft revealed strong beaming of these particles along the direction of the large-scale magnetic field. Since such large anisotropies exclude the use of standard cosmic-ray transport theory for nearly isotropic particle distributions in modeling the acceleration of these particles at the Termination Shock, we developed a Shock acceleration model based on the numerical solution of the standard focused kinetic transport equation. After investigating the appropriateness of the physical content of this equation for Shock acceleration, and applying the model to Shocks of varying Shock obliquity, we find that (1) this approach is a viable alternative to more sophisticated particle codes such as hybrid codes for simulating the Shock acceleration of pickup ions and (2) that the model has the potential to reproduce many of the interesting features of energetic ions observed by the Voyager spacecraft at the Termination Shock.
Aaron Barnes - One of the best experts on this subject based on the ideXlab platform.
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Motion of the Heliospheric Termination Shock
2004Co-Authors: Kamcilla Naidu, Aaron BarnesAbstract:In this paper we generalize earlier gasdynamic analyses of the motion of the heliospheric Termination Shock in response to upstream disturbances to include magnetohydrodynamic (MHD) phenomena. We assume that the Termination Shock is a strong, perpendicular Shock and that the initial upstream disturbance is a tangential discontinuity. The resulting configuration after the interaction is very similar to that in the gasdynamic models after an interaction with a contact discontinuity or interplanetary Shock, and for an increase (decrease) in dynamic pressure consists of an outward (inward) propagating Termination Shock and an outward propagating Shock (MHD rarefaction wave) that carries the signal of the disturbance into the far downstream plasma. The plasma immediately behind the new Termination Shock is separated from the downstream signal by a tangential discontinuity. The results of the model show that the speed of the new Termination Shock depends mainly on the magnitude of the change in dynamic pressure and are typically of order -100 km/s, comparable to the results of the gasdynamic models.
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Geometry of the Termination Shock
AIP Conference Proceedings, 2004Co-Authors: Aaron BarnesAbstract:This paper is a brief survey of theoretical expectations for the geometry of the heliospheric Termination Shock.
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Shape of the heliospheric Termination Shock: Effects of latitude variations of solar wind dynamic pressure
Journal of Geophysical Research: Space Physics, 1998Co-Authors: Aaron BarnesAbstract:We investigate the consequences of internal solar wind latitude variations on the heliospheric Termination Shock and the flow of the gas beyond the Shock. We have developed a simple gasdynamic model, assuming the solar wind to be a steady, axially symmetric radial outflow of gas that passes through a Termination Shock and flows incompressibly beyond the Shock. We ignore any latitude variations external to the heliosphere (i.e., due to the local interstellar medium) by requiring that the stagnation pressure infinitely far away must be spherically symmetric. Analysis of the model leads to three broad conclusions: (1) The shape of the heliospheric Shock is qualitatively similar to what one would predict using the “naive” assumption that the heliocentric distance of the Shock is proportional to the square root of the scaled solar wind dynamic pressure ρvr2. (2) However, the existence of an internal latitude dependence of the scaled dynamic pressure requires that the Shock must be oblique at some latitudes, and this obliquity produces an outward “bulge” in the shape of the Termination Shock; this conclusion is completely general, and in particular is true for the case of an oblate Shock. (3) For a prolate Termination Shock the far-down-stream flow is deflected toward the equator, and solar wind originating in the poleward half of (say) the northern hemisphere would fill more than half of the volume of the same hemisphere beyond the Termination Shock; the deflection would be in the opposite sense (poleward) for an oblate Termination Shock.
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Heliospheric Termination Shock motion in response to LISM variations: Spherically symmetric model
Geophysical Research Letters, 1997Co-Authors: Romana Ratkiewicz, Aaron Barnes, J. R. SpreiterAbstract:The unsteady spherically symmetric one-dimensional gasdynamic model appears to be a powerful tool in the investigation of the Termination Shock motion. Such a model has previously been used to examine the response of the heliospheric Termination Shock to variations in upstream solar wind conditions [Ratkiewicz et al., 1996]. In the current paper we apply the same model to study response of the Shock to variations in the interstellar medium. The initial-boundary conditions for the unsteady calculations are given by the pressure as a function of time on an outer boundary either alone or with the density as a function of time on an inner boundary. The motion of the Termination Shock is caused by fluctuations in both solar wind and interstellar plasma parameters and has a rather complicated behavior, characterized by a sequence of perturbations that hit the Termination Shock and are reflected from the outer boundary.
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Global aspects of the motion of the heliospheric Termination Shock: A gasdynamic model
1995Co-Authors: R. Ratkiewicz, Aaron Barnes, G. A. MolvikAbstract:The heliospheric Termination Shock is expected to move in response to variation in upstream solar wind conditions. Using numerical techniques, we extend an earlier strictly one-dimensional analytic gas dynamic model of Shock motion to two dimensions, to investigate the qualitative features of global behavior of Shock motion, and the consequences of latitudinal variation in dynamic pressure. The boundary conditions of the calculation are given by the solar wind parameters as a function of latitude and time on an inner spherical boundary, and a constant pressure (roughly simulating the effect of the local interstellar medium) on an outer boundary. Density variations, specified at the inner boundary as a function of time, are convected into the Termination Shock. Immediately after the interaction, the Shock moves with speeds given by the earlier analytic model. However, as the Termination Shock propagates outward (or inward), it begins to slow down. After about 2 to 10 years, depending on details of boundary conditions, the signal from the Shock interaction has reached the outer boundary and propagates inward to the position of the Termination Shock, strongly affecting the behavior of the Shock. Assuming no further disturbances in the solar wind, the Termination Shock will reach its new equilibrium after some tens of years. In reality, large-scale variations in solar wind dynamic pressure occur on time scales short in comparison with the eleven year solar cycle, so that one expects that the Termination Shock is never in an equilibrium position, but rather oscillates inward and outward; this oscillation will vary with heliographic latitude. The effects of a variety of types of solar wind disturbances are investigated and summarized.
Y. C. Whang - One of the best experts on this subject based on the ideXlab platform.
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THE Termination Shock MAY HAVE A BOW-SHAPED OPEN GEOMETRY
The Astrophysical Journal, 2011Co-Authors: Y. C. WhangAbstract:The global Termination Shock has been calculated by many authors. All show that the Shock has a closed geometry for which the Termination Shock encompasses the Sun. This research points out that there exists another possibility: that the Termination Shock may have an open geometry in which the Shock on the upwind side flares out along the sides, so that the supersonic solar wind remains Shock free on the downwind side in the heliotail. Interaction of the solar wind with the interstellar medium leads to the formation of the heliosphere and Termination Shock. The interaction causes substantial disturbances on both sides of the heliopause. On the heliosphere side, the magnetic field and plasma flow are significantly compressed as the heliopause blocks the forward motion of the supersonic solar wind; this mechanism is responsible for the formation of the Termination Shock on the upwind side. However, on the downwind side the motion of supersonic solar wind is unobstructed. There is no repeat of the kind of intense solar wind interstellar interaction like that which occurs on the upwind side. The mechanism for Shock formation is not present on the downwind side; thus, the global Termination Shock likely has an open geometry. An example is obtained to demonstrate global characteristics of the Termination Shock with a bow-shaped open geometry. The Shock is a normal Shock at the nose point. The Shock weakens along the Shock surface from the nose to its flanks; eventually, the Shock asymptotically reduces to a Mach wave.
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Solar cycle variation of the Termination Shock
AIP Conference Proceedings, 2004Co-Authors: Y. C. WhangAbstract:We studied the Termination Shock near the ecliptic, and near 35° latitude on the upwind side of the heliosphere. The Shock location is solar cycle dependent; the Shock moves outwards and inwards over timescales of a solar cycle in response to the variations in the average solar wind speed. The maximum distance occurs during the rising phase of the solar cycle, and the minimum distance during the declining phase; the amplitude increases with the latitude. Shock parameters are distinctly different when the Shock moves outwards or inwards. If Voyager 1 did cross the Termination Shock in 2002.6, the spacecraft would likely cross the Shock at least two more times before 2010. If Voyager 1 did not cross the Termination Shock in 2002, it might still do so very soon.
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The Termination Shock near 35° latitude
Geophysical Research Letters, 2004Co-Authors: Y. C. Whang, Leonard F. Burlaga, Y.-m. Wang, N. R. SheeleyAbstract:[1] The Termination Shock moves outwards and inwards over timescales of a solar cycle in response to the variations in the average solar wind speed. The amplitude is greater than 50 AU near 35° latitude; the maximum (minimum) distance occurs during the rising (declining) phase of the solar cycle. Shock parameters are distinctly different when the Shock moves outwards or inwards. During the period of high-speed (low-speed) solar wind, the Shock moves outward (inward) and the Shock is weaker (stronger). This study assumes that the first crossing of Voyager 1 with the Termination Shock occurred at 85.5 AU on 2002.6. If Voyager 1 did cross the Shock in 2002.6, the spacecraft would likely cross the Shock at least two more times before 2010, but no second crossing would occur close to 2003.1. If Voyager 1 did not cross the Shock in mid-2002, it might still do so before 2005.
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Voyager crossing of the Termination Shock: prediction
Advances in Space Research, 2002Co-Authors: Y. C. Whang, Leonard F. BurlagaAbstract:Abstract This paper studies the varying location and conditions of the Termination Shock over 34-year period (1966 – 2000). The Shock location is anti-correlated with the sunspot number, moving inward or outward during the rising or declining phase of the solar cycle. For the Shock in the upwind direction, plasma and magnetic field conditions in its immediately upstream are extrapolated from 1 AU data using MHD equations including pickup protons, and the Shock location estimated by the ACR spectrum is used as a guide. Voyager 1 will cross the Termination Shock in the region of high-speed solar wind at latitude of ∼34°. Taking into consideration the high-latitude effects, the calculation indicates that the Shock is now moving inward to within 85 AU. Voyager 1 could cross the Shock around Year 2002, and the crossing may occur 3 or more times over a period of about 4 years.
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Anticipated Voyager crossing of the Termination Shock
Geophysical Research Letters, 2000Co-Authors: Y. C. Whang, Leonard F. BurlagaAbstract:This paper studies the varying location and conditions of the Termination Shock over 34-year period (1966 – 2000). The Shock location is anti-correlated with the sunspot number, moving inward or outward during the rising or declining phase of the solar cycle. For the Shock in the upwind direction, plasma and magnetic field conditions in its immediately upstream are extrapolated from 1 AU data using MHD equations including pickup protons, and the Shock location estimated by the ACR spectrum is used as a guide. Voyager 1 will cross the Termination Shock in the region of high-speed solar wind at latitude of ∼34°. Taking into consideration the high-latitude effects, the calculation indicates that the Shock is now moving inward to within 85 AU. Voyager 1 could cross the Shock before Year 2002, and the crossing may occur 3 or more times over a period of about 4 years.
G. M. Webb - One of the best experts on this subject based on the ideXlab platform.
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time dependent acceleration of interstellar pickup ions at the heliospheric Termination Shock using a focused transport approach
The Astrophysical Journal, 2009Co-Authors: J Le A Roux, G. M. WebbAbstract:A time-dependent focused transport approach to modeling diffusive Shock acceleration of interstellar pickup ions at the Termination Shock is discussed. By taking into account time variations in the magnetic field angle, and thus by implication in the Shock obliquity and injection speed at the Termination Shock using Voyager 1 observations as guide, we show that unaccelerated core interstellar pickup protons can be accelerated by the nearly perpendicular Termination Shock at the heliospheric nose. Many features of anomalous cosmic rays, observed by the Voyager spacecraft at energies below the big spectral dip starting at ~3 MeV, can be successfully reproduced with this approach. This includes multiple power-law spectral slopes with stable breaking points, power-law spectral slopes that are harder than predicted by standard diffusive Shock acceleration, large pitch-angle anisotropies with strong time variations upstream that converge to steady-state isotropy in the heliosheath, upstream pitch-angle anisotropies that peak at ~1 MeV, episodic strongly anisotropic intensity spikes at the Termination Shock, and strong spectral volatility upstream that is reduced downstream and almost completely disappears farther downstream.
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Micro‐Structure of the Heliospheric Termination Shock
AIP Conference Proceedings, 2009Co-Authors: G. P. Zank, R. H. Burrows, M. Oka, B. Dasgupta, Jacob Heerikhuisen, G. M. WebbAbstract:Observations by the Voyager 2 spacecraft of the structure of the heliospheric Termination Shock revealed a quasi‐perpendicular structure that possessed many of the characteristics that are familiar to us from perpendicular Shocks observed in the inner heliosphere. However, a surprise was the relative lack of heating experienced by thermal solar wind ions (and electrons), leading to the suggestion that the pickup ions were primarily heated at the heliospheric Termination Shock. Because the Voyager plasma instrument cannot measure the interstellar pickup ions directly, their behavior at the Termination Shock could not be gauged directly. Nonetheless, it had already been predicted [16] that the primary dissipation mechanism for the quasi‐perpendicular Termination Shock would be the reflection of pickup ions rather than solar wind ions; this because of the shell‐like structure of the pickup ion distribution function. We discuss the effect of pickup ions including their trajectories within the structure of the Shock observed by Voyager 2. A model for the Shock structure is constructed on the basis of preferentially reflected pickup ions, solutions are discussed, and we estimate the degree of heating for the various components.
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Termination Shock Surfing
AIP Conference Proceedings, 2009Co-Authors: R. H. Burrows, G. P. Zank, G. M. WebbAbstract:The recent Voyager 2 (V2) observations of the Termination Shock (TS) indicate that it is a plasma Shock like no other in the heliosphere with dynamics and structure heavily influenced by the presence of an energized population of pickup ions (PUIs). The ‘unexpected’ finding of a cold plasma in the heliosheath with very little heating of the solar wind suggests that the energy dissipated by the Shock could be dominated by the acceleration of PUIs at the TS. We examine the ’Shock surfing’ mechanism at the test particle level, where multiply reflected ions (MRIs) gain energy from the motional electric field as a consequence of reflection from the cross‐Shockpotential, for a specific model of the TS3 (the third TS crossing measured by V2). The energization of PUI shell distributions at a stationary, perpendicular model of the TS3 indicate that Shock surfing can provide substantial PUI acceleration and a dissipation mechanism at the TS. For a strong enough cross‐Shock potential and sufficiently narrow Shock ra...
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A FOCUSED TRANSPORT APPROACH TO PICKUP ION Shock ACCELERATION: IMPLICATIONS FOR THE Termination Shock
The Astrophysical Journal, 2007Co-Authors: J. A. Le Roux, G. M. Webb, Vladimir Florinski, G. P. ZankAbstract:The discovery of low-energy suprathermal ions coming directly from the solar wind Termination Shock by the Voyager 1 spacecraft revealed strong beaming of these particles along the direction of the large-scale magnetic field. Since such large anisotropies exclude the use of standard cosmic-ray transport theory for nearly isotropic particle distributions in modeling the acceleration of these particles at the Termination Shock, we developed a Shock acceleration model based on the numerical solution of the standard focused kinetic transport equation. After investigating the appropriateness of the physical content of this equation for Shock acceleration, and applying the model to Shocks of varying Shock obliquity, we find that (1) this approach is a viable alternative to more sophisticated particle codes such as hybrid codes for simulating the Shock acceleration of pickup ions and (2) that the model has the potential to reproduce many of the interesting features of energetic ions observed by the Voyager spacecraft at the Termination Shock.
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Acceleration of pickup ions at the Termination Shock
AIP Conference Proceedings, 2006Co-Authors: J. A. Le Roux, G. M. WebbAbstract:With a model based on the numerical solution of the standard focused transport equation we investigated the acceleration of ∼ 1 keV interstellar pickup protons at a reverse Shock with an obliquity of 45°. We found that the model reproduces the basic spectral features of more sophisticated hybrid codes. The model also explains in principle the Voyager 1 observations of large upstream anisotropies and intensity spikes near the Termination Shock associated with the newly discovered Termination Shock particle component. Magnetic mirroring of pick up ions at the Shock plays a crucial role in this regard. We discuss how this approach can work at the actual nearly perpendicular Termination Shock.
G. P. Zank - One of the best experts on this subject based on the ideXlab platform.
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an energetic particle mediated Termination Shock observed by voyager 2
Geophysical Research Letters, 2009Co-Authors: V. Florinski, J Le A Roux, R B Decker, G. P. ZankAbstract:[1] Voyager 2 crossed the solar wind Termination Shock several times during August 30 – September 1 of 2007. During the last forty days before the crossing intensities of energetic ions measured by the LECP instrument were increasing exponentially, and their spectrum showed clear evidence of unfolding at low energies. Plasma data featured a broad velocity precursor, where solar wind speed decreased from about 380 km/s far upstream to ∼300 km/s at the Shock. By using plasma and energetic particle conservation laws we demonstrate that the speed decrease during Voyager 2's last ∼40 days in the solar wind could be plausibly produced by the back-pressure of energetic ions with energies of a few MeV on the upstream plasma flow. These particles propagate diffusively upstream from the Termination Shock, producing a Shock precursor that has a characteristic lengthscale of 0.35 AU, assuming the Shock has not moved substantially during that time.
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MHD analysis of the time‐varying Termination‐Shock position
AIP Conference Proceedings, 2008Co-Authors: H. Washimi, G. P. Zank, T. Tanaka, K. MunakataAbstract:A realistic and time‐varying Termination Shock position is studied by using three‐dimensional MHD simulation. The effect of heliospheric disturbances on the position of the Termination Shock (TS) is examined in some detail by using model of (1) rectangular‐type periodic change and (2) triangle‐type pulse of the solar‐wind ram‐pressure. Comparing study of our forecasting simulation (Washimi et al. 2007B) with observed V2‐TS crossing enables us a new prospect of the heliospheric structure. It is discussed that the heliosphere can be skewed not only by N‐S asymmetry, which is produced by obliquely oriented interstellar magnetic field, but also by some TS‐depression in lower latitudes.
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do anomalous cosmic rays modify the Termination Shock
The Astrophysical Journal, 2004Co-Authors: V. Florinski, J.r. Jokipii, E. C. Stone, G. P. Zank, A. C. CummingsAbstract:This work extends our previous two-dimensional self-consistent model of the cosmic rays interacting with the solar wind to include anomalous cosmic rays. As before, energetic particles are described kinetically using a Parker equation. The model includes diffusion, convection, and drift effects, as well as Shock and compression acceleration and expansion cooling by nonuniform solar wind flow. A new numerical model has been developed featuring an adaptive-mesh refinement algorithm to accommodate small diffusive length scales of low-energy Shock-accelerated particles. We show that anomalous cosmic rays have only a minor effect on the Termination Shock during the time near solar minima. Specifically, cosmic-ray gradients cause the subShock to move away from the Sun by about 1 AU with its compression ratio decreasing by about 5% compared to the reference case without cosmic-ray effects. We also study the effect of solar wind slowdown by charge exchange downstream of the Termination Shock, producing compressive flow in this region and resulting in additional acceleration of anomalous cosmic rays in the heliosheath. For the first time, spectra calculated with our self-consistent model show a good agreement with the cosmic-ray data from the two Voyager spacecraft, giving more confidence in the model predictions than the previous parametric studies.
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The response of a gasdynamic Termination Shock to interplanetary disturbances
Journal of Geophysical Research, 1995Co-Authors: T. R. Story, G. P. ZankAbstract:A one-dimensional gasdynamic model is used to analyze the interaction of the solar wind Termination Shock (TS) with various interplanetary disturbances. These include density enhancements and depletions, Gaussian Shock pulses, and forward-reverse Shock pairs. Our simulations suggest that the Termination Shock is unlikely to be stationary. Both the interaction state and the postinteraction state of the Termination Shock are discussed. The very complicated state and structure of the TS during interaction with interplanetary disturbances is examined carefully. It is found that the TS is not readily identifiable from the other simultaneously present structures (reverse Shock, contact discontinuities, forward Shocks and so on.). This may complicate the identification of the TS by the Voyager or Pioneer spacecraft significantly. It is also found that a number of interesting structures propagate and evolve downstream after a collision. These include sharp spikes in the density, which advect outward at the postShock flow speed, and secondary damped Shock pulses produced in the collision, which propagate supersonically. Some implications of both the density enhancements and the production of damped Shock waves in the heliosheath and at the heliopause are discussed
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Steady state and dynamical structure of a cosmic-ray-modified Termination Shock
Journal of Geophysical Research: Space Physics, 1993Co-Authors: D. J. Donohue, G. P. ZankAbstract:A hydrodynamic model is developed for the structure of a cosmic-ray-modified Termination Shock. The model is based on the two-fluid equations of diffusive Shock acceleration (Drury and Volk, 1981). Both the steady state structure of the Shock and its interaction with outer heliospheric disturbances are considered. Under the assumption that the solar wind is decelerated by diffusing interstellar cosmic rays, it is shown that the natural state of the Termination Shock is a gradual deceleration and compression, followed by a discontinuous jump to a downstream state which is dominated by the pressure contribution of the cosmic rays. A representative model is calculated for the steady state which incorporates both interstellar cosmic ray mediation and diffusively accelerated anomalous ions through a proposed thermal leakage mechanism. The interaction of large-scale disturbances with the equilibrium Termination Shock model is shown to result in some unusual downstream structure, including transmitted Shocks and cosmic-ray-modified contact discontinuities. The structure observed may be connected to the 2-kHz outer heliospheric radio emission (Cairns et al., 1992a, b). The time-dependent simulations also demonstrate that interaction with solar wind compressible turbulence (e.g., traveling interplanetary Shocks, etc.) could induce the Termination Shock to continually fluctuate between cosmic-ray-dominated and gas-dynamic states. This fluctuation may represent a partial explanation of the galactic cosmic ray modulation effect and illustrates that the Pioneer and Voyager satellites will encounter an evolving Shock whose structure and dynamic properties are strongly influenced by the mediation of interstellar and anomalous cosmic rays.
