Solar wind bulk velocity fluctuations acting as velocity space diffusion on comoving ions

Fahr, H. J.; Чашей, И. В.; Siewert, M.

doi:10.1051/0004-6361/201117503

Cited by 12 publications

(6 citation statements)

References 18 publications

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“…Such increased ribbon fluxes can also be understood in terms of the scenario outlined above. On the one hand, all explanations based on a heliospheric source of ENAs (e.g., Fahr et al 2012;Siewert et al 2013) would apply as well -an Hwave would simply enhance the effects. On the other hand, one should note that the region where the H-wave intersects the heliopause is possibly also a region of both perturbed plasma (in phase with the neutral perturbation, see Diver et al 2006) and the strongest deformation of the interstellar magnetic field due to the "obstacle" heliosphere (Schwadron et al 2009;Pogorelov et al 2011), see Fig.…”

Section: Ribbon Spectramentioning

confidence: 99%

The IBEX ribbon as a signature of the inhomogeneity of the local interstellar medium

Fichtner

Scherer

Effenberger

et al. 2014

A&A

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Context.A new hypothesis is offered to explain the so-called ribbon feature appearing in the all-sky flux maps of energetic neutral atoms presently observed with the IBEX spacecraft, namely that the ribbon is a consequence of inhomogeneities in the local interstellar medium. Aims. The study aims at a detailed presentation of this hypothesis and its implications for the interpretation of ENA measurements with IBEX. Methods. Theoretical considerations regarding three different topics, namely IBEX measurements related to high-energy neutral atoms, Lyman-α observations (made with the Voyager 1 spacecraft) related to low-energy neutral atoms, and astronomical data related to the structure of the interstellar medium, are critically discussed in order to corroborate the hypothesis. Results. It is found that inhomogeneities in the local interstellar medium can explain not only the IBEX ribbon and outer heliospheric Lyman-α observations, but can also account for the interstellar Lyman-α absorption that could only with difficulty be fully attributed to the hydrogen wall in the outer heliosheath if the heliospheric bow shock would indeed be absent. Conclusions. The IBEX observations of the ribbon provide a unique opportunity to learn more about the nature of the interstellar medium surrounding the heliosphere.

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Section: Ribbon Spectramentioning

confidence: 99%

The IBEX ribbon as a signature of the inhomogeneity of the local interstellar medium

Fichtner

Scherer

Effenberger

et al. 2014

A&A

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“…Especially in the outer heliosphere (r ≥ 5 AU), the ion pressure is dominated by the pick-up-ion pressures on either side of the jump. Under this assumption, the expressions for the ion pressures are significantly simplified (see Fahr et al 2012) for a perpendicular jump (ΔU ⊥ B), leading to…”

Section: Change Of Compression Due To Work Done Against Entropized Pimentioning

confidence: 99%

Traveling solar-wind bulk-velocity fluctuations and their effects on electron heating in the heliosphere

Fahr

Чашей

Verscharen

2014

A&A

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Ambient plasma electrons undergo strong heating in regions associated with compressive bulk-velocity jumps ΔU that travel through the interplanetary solar wind. The heating is generated by their specific interactions with the jump-inherent electric fields. After this energy gain is thermalized by the shock passage through the operation of the Buneman instability, strong electron heating occurs that substantially influences the radial electron temperature profile. We previously studied the resulting electron temperature assuming that the amplitude of the traveling velocity jump remains constant with increasing solar distance. Now we aim at a more consistent view, describing the change in jump amplitude with distance that is caused by the heated electrons. We describe the reduction of the jump amplitude as a result of the energy expended by the traveling jump structure. We consider three effects: energy loss due to heating of electrons, energy loss due to work done against the pressure gradient of the pick-up ions, and an energy gain due to nonlinear jump steepening. Taking these effects into account, we show that the decrease in jump amplitude with solar distance is more pronounced when the initial jump amplitude is higher in the inner solar system. Independent of the initial jump amplitude, it eventually decreases with increasing distance to a value of about ΔU/U 0.1 at the position of the heliospheric termination shock, where ΔU is the jump amplitude, and U is the average solar-wind bulk velocity.The electron temperature, on the other hand, is strongly correlated with the initial jump amplitude and leads to electron temperatures between 6000 K and 20 000 K at distances beyond 50 AU. We compare our results with in situ measurements of the electron-core temperature from the Ulysses spacecraft in the plane of the ecliptic for 1.5 AU ≤ r ≤ 5 AU, where r is the distance from the Sun. Our results agree very well with these observations, which corroborates our extrapolated predictions beyond r = 5 AU.

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“…A change from the widely known isotropic Kolmogorov (D(v)∝v 2/3 ; e.g., Isenberg 1987) and anisotropic Goldreich-Sridhar (D(v)∝v 2 ; e.g., Goldreich & Sridhar 1995; Eichler 2014) turbulence spectra suggests that the presence of PUIs, which constitute a significant fraction of the plasma density far from the TS, may be modifying the turbulence spectrum. We note also that particle interactions with compressive waves may also result in D(v)∝v 2 (see e.g., Toptyghin 1980;Chalov et al 2003;le Roux et al 2005;Fahr et al 2012;Zhang & Lee 2013).…”

Section: Discussionmentioning

confidence: 90%

Constraining the Evolution of the Proton Distribution Function in the Heliotail

Zirnstein

Kumar

Heerikhuisen

et al. 2018

ApJ

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We use Interstellar Boundary Explorer (IBEX) measurements of energetic neutral atoms (ENAs) to constrain the proton (mostly pickup ion, PUI) distribution in the heliotail. In our previous study, we solved the Parker transport equation and found that the velocity diffusion coefficient D(v) for PUIs is approximately D(v)∼1.1× 10 −8 km 2 s −3 (v/v 0 ) 1.3 , assuming the initial proton distribution processed by the termination shock (TS), f p,0 , is a kappa distribution with kappa index κ p,0 =1.63. In this study, we test different forms for f p,0 . WeWhile the case where D(v)∝v 1.3 yields ENA fluxes that appear to best reproduce IBEX data for any κ p,0 , it is possible for D(v) to scale close to ∼v 2/3 or ∼v 2 within our uncertainties by changing D 0 . We also show that an upstream PUI filled-shell distribution that is heated by a quasi-stationary TS, generating a downstream filled-shell with large cutoff speed, yields an excess of ENAs>2 keV compared to IBEX. However, using a fully kinetic particle-in-cell simulation to process a PUI filled-shell across the TS yields ENA spectra consistent with IBEX, reinforcing the significance of self-consistent, preferential PUI heating and diffusion at the TS. Interestingly, an upstream PUI distribution inferred from the particle-in-cell simulation to reproduce Voyager 2 observations of the nose-ward TS is inconsistent with IBEX observations from the heliotail, suggesting differences in the upstream PUI distribution or TS properties.

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Solar wind bulk velocity fluctuations acting as velocity space diffusion on comoving ions

Cited by 12 publications

References 18 publications

The IBEX ribbon as a signature of the inhomogeneity of the local interstellar medium

The IBEX ribbon as a signature of the inhomogeneity of the local interstellar medium

Traveling solar-wind bulk-velocity fluctuations and their effects on electron heating in the heliosphere

Constraining the Evolution of the Proton Distribution Function in the Heliotail

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