Voyagers 1 and 2 in a shrunken and squashed heliosphere

Webber, W. R.; Intriligator, D. S.

doi:10.1029/2011ja016478

Cited by 14 publications

(12 citation statements)

References 29 publications

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“…The HSTOF results for the period 1996−2005 imply the thickness (in the forward sector) of ∼20−30 AU, similar to the result of Hsieh et al (2010) (21−28 AU) and of Krimigis et al (2011) (27 AU for Voyager 1 direction). A similar distance to the heliopause (112−128 AU) was obtained in a semiempirical model by Webber and Intriligator (2011). One implication is that Voyager 1 should be already close to the outer boundary of the heliosphere.…”

Section: Discussionmentioning

confidence: 48%

HSTOF ENA observations and energetic ion distributions in the heliosheath

Czechowski

Hilchenbach

Hsieh

2012

A&A

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Context. Launched in 1996, HSTOF on board SOHO was the first instrument to detect the energetic neutral atoms (ENA) from the heliosheath. After mid 2003, the field of view of HSTOF was restricted to the flank sectors of the heliosheath, in which region the energetic ion distributions are still unknown. Interpretation of these data requires understanding of the energetic ion transport in the inner heliosheath. Aims. We update the HSTOF ENA hydrogen and helium spectra by adding the results from the recent (2006−2010) measurements. We calculate the energetic ion distributions in a numerical model of the heliosheath and use them as a basis for interpreting the HSTOF ENA observations, in particular those of the flank sectors. Methods. The hydrogen and helium ENA spectra were derived from the HSTOF observations of two 90 • -wide ecliptic longitude sectors around the crosswind directions. The energetic ion distributions in the heliosheath were calculated in a simple model of the heliosphere, assuming that the main acceleration occurs at the termination shock. The effects of different processes (charge-exchange loss, adiabatic acceleration, parallel diffusion and escape across the boundary) were determined with different assumptions about the boundary conditions and the transport parameters. The resulting ion distributions were used to calculate the ENA fluxes, which can be compared with the observations by HSTOF and other instruments. Results. The energetic ion density in the flank sectors of the heliosphere is lower than in the forward (upwind) sector. As a result, the contribution of the flanks of the heliosheath to the production of ENA is not directly proportional to the thickness of the heliosheath, but instead is comparable to the contribution of the forward sector, which agrees with the HSTOF data. The HSTOF ENA flux intensity is nevertheless significantly lower than the model calculations. Near the heliopause there appears a region of low energetic ion density caused by the charge-exchange and the escape losses.

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Section: Discussionmentioning

confidence: 48%

HSTOF ENA observations and energetic ion distributions in the heliosheath

Czechowski

Hilchenbach

Hsieh

2012

A&A

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“…Our finding supports the speculation that the heliosphere is shrinking. 67,71) In general, our IPS observations demonstrate that the 3D structure of the solar wind undergoes a drastic change in response to the peculiar solar dynamo activity.…”

Section: Solar Cycle Variation Of the Solar Wind Structurementioning

confidence: 65%

Three-dimensional exploration of the solar wind using observations of interplanetary scintillation

Tokumaru

2013

Proc. Jpn. Acad., Ser. B

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The solar wind, a supersonic plasma flow continuously emanating from the Sun, governs the space environment in a vast region extending to the boundary of the heliosphere (∼100 AU). Precise understanding of the solar wind is of importance not only because it will satisfy scientific interest in an enigmatic astrophysical phenomenon, but because it has broad impacts on relevant fields. Interplanetary scintillation (IPS) of compact radio sources at meter to centimeter wavelengths serves as a useful ground-based method for investigating the solar wind. IPS measurements of the solar wind at a frequency of 327 MHz have been carried out regularly since the 1980s using the multi-station system of the Solar-Terrestrial Environment Laboratory (STEL) of Nagoya University. This paper reviews new aspects of the solar wind revealed from our IPS observations.

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“…The scenario with r ts = 90 AU (dashed blue line) is considered the reference scenario, which produces the best fit when compared to observations. It is known that the TS position is changing as a function of solar activity (Scherer and Fahr, 2003;Webber and Intriligator, 2011) and is therefore not stationary, as assumed here. The purpose of this section however is to show the sensitivity of the computed intensities to the position of the shock.…”

Section: Effect Of Different Heliopause Positionsmentioning

confidence: 99%

Time-Dependent Modulation of Cosmic Rays in the Heliosphere

2013

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The time-dependent modulation of galactic cosmic rays in the heliosphere is studied by computing intensities using a time-dependent modulation model. By introducing recent theoretical advances in the transport coefficients in the model, computed intensities are compared with Voyager 1, International Monitoring Platform (IMP) 8, and Ulysses proton observations in search of compatibility. The effect of different modulation parameters on computed intensities is also illustrated. It is shown that this approach produces, on a global scale, realistic cosmic-ray proton intensities along the Voyager 1 spacecraft trajectory and at Earth upto ∼2004, whereafter the computed intensities recovers much slower towards solar minimum than observed in the inner heliosphere. A modified time dependence in the diffusion coefficients is proposed to improve compatibility with the observations at Earth after ∼2004. This modified time dependence led to an improved compatibility between computed intensities and the observations along the Voyager 1 trajectory and at Earth even after ∼2004. An interesting result is that the cosmic-ray modulation during the present polarity cycle is not determined only by changes in the drift coefficient and tilt angle of the wavy current sheet, but is also largely dependent on changes in the diffusion coefficients.

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Voyagers 1 and 2 in a shrunken and squashed heliosphere

Cited by 14 publications

References 29 publications

HSTOF ENA observations and energetic ion distributions in the heliosheath

HSTOF ENA observations and energetic ion distributions in the heliosheath

Three-dimensional exploration of the solar wind using observations of interplanetary scintillation

Time-Dependent Modulation of Cosmic Rays in the Heliosphere

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