Found 15 results
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Filters: Keyword is Sun: heliosphere  [Clear All Filters]
2019
Authors: Riley Pete, Downs Cooper, Linker Jon A., Mikic Zoran, Lionello Roberto, et al.
Title: Predicting the Structure of the Solar Corona and Inner Heliosphere during Parker Solar Probe 's First Perihelion Pass
Abstract:

NASA’s Parker Solar Probe (PSP) spacecraft reached its first perihelion of 35.7 solar radii on 2018 November 5. To aid in mission planning, and in anticipation of the unprecedented measurements to be returned, in late October, we developed a three-dimensional magnetohydrodynamic (MHD) solution for the solar corona and inner heliosphere, driven by the then available observations of the Sun’s photospheric magnetic field. Our model incorporates a wave-turbulence-driven model to heat the corona. Here, we present our predictions for the structure of the solar corona and the likely in situ measurements that PSP will be returning over the next few months. We infer that, in the days prior to first encounter, PSP was immersed in wind emanating from a well-established, positive-polarity north. . .
Date: 04/2019 Publisher: The Astrophysical Journal Pages: L15 DOI: 10.3847/2041-8213/ab0ec3 Available at: http://stacks.iop.org/2041-8205/874/i=2/a=L15?key=crossref.94a3f13ef95cab063c2cc60115d0f410http://stacks.iop.org/2041-8205/874/i=2/a=L15/pd
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Authors: Perrone Denise, Stansby D, Horbury T S, and Matteini L
Title: Thermodynamics of pure fast solar wind: radial evolution of the temperature–speed relationship in the inner heliosphereABSTRACT
Abstract:

A strong correlation between speed and proton temperature has been observed, across many years, on hourly averaged measurements in the solar wind. Here, we show that this relationship is also observed at a smaller scale on intervals of a few days, within a single stream. Following the radial evolution of a well-defined stream of coronal-hole plasma, we show that the temperature-speed (T-V) relationship evolves with distance, implying that the T-V relationship at 1 au cannot be used as a proxy for that near the Sun. We suggest that this behaviour could be a combination of the anticorrelation between speed and flux-tube expansion factor near the Sun and the effect of a continuous heating experienced by the plasma during the expansion. We also show that the cooling index for the radial evo. . .
Date: 09/2019 Publisher: Monthly Notices of the Royal Astronomical Society Pages: 2380 - 2386 DOI: 10.1093/mnras/stz1877 Available at: https://academic.oup.com/mnras/article/488/2/2380/5530769http://academic.oup.com/mnras/article-pdf/488/2/2380/28979632/stz1877.pdfhttp://academic.oup.com/mnras/advance-article-pdf/doi/10.1093/mnras/stz1877/28924256/stz1877.pdf
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2018
Authors: Stansby D, Horbury T S, and Matteini L
Title: Diagnosing solar wind origins using in situ measurements in the inner heliosphere
Abstract:

Robustly identifying the solar sources of individual packets of solar wind measured in interplanetary space remains an open problem. We set out to see if this problem is easier to tackle using solar wind measurements closer to the Sun than 1 au, where the mixing and dynamical interaction of different solar wind streams is reduced. Using measurements from the Helios mission, we examined how the proton core temperature anisotropy and cross-helicity varied with distance. At 0.3 au there are two clearly separated anisotropic and isotropic populations of solar wind that are not distinguishable at 1 au. The anisotropic population is always Alfvénic and spans a wide range of speeds. In contrast the isotropic population has slow speeds, and contains a mix of Alfvénic wind with constant mass f. . .
Date: 01/2019 Publisher: Monthly Notices of the Royal Astronomical Society Pages: 1706 - 1714 DOI: 10.1093/mnras/sty2814 Available at: https://academic.oup.com/mnras/article/482/2/1706/5142296http://academic.oup.com/mnras/article-pdf/482/2/1706/26330049/sty2814.pdf
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Authors: Graham G. A., Rae I. J., Owen C. J., and Walsh A. P.
Title: Investigating the Effect of IMF Path Length on Pitch-angle Scattering of Strahl within 1 au
Abstract:

Strahl is the strongly field-aligned, beam-like population of electrons in the solar wind. Strahl width is observed to increase with distance from the Sun, and hence strahl electrons must be subject to in-transit scattering effects. Different energy relations have been both observed and modeled for both strahl width and the width increase with radial distance. Thus, there is much debate regarding what mechanism(s) scatter strahl. In this study, we use a novel method to investigate strahl evolution within 1 au by estimating the distance traveled by the strahl along the interplanetary magnetic field (IMF). We do this by implementing methods developed in previous studies, which make use of the onset of solar energetic particles at ̃1 au. Thus, we are able to obtain average strahl broadeni. . .
Date: 03/2018 Publisher: The Astrophysical Journal Pages: 40 DOI: 10.3847/1538-4357/aaaf1b Available at: http://stacks.iop.org/0004-637X/855/i=1/a=40?key=crossref.ef4d8c88b914db7976655ab16f8f792a
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Authors: Hu Junxiang, Li Gang, Fu Shuai, Zank Gary, and Ao Xianzhi
Title: Modeling a Single SEP Event from Multiple Vantage Points Using the iPATH Model
Abstract:

Using the recently extended 2D improved Particle Acceleration and Transport in the Heliosphere (iPATH) model, we model an example gradual solar energetic particle event as observed at multiple locations. Protons and ions that are energized via the diffusive shock acceleration mechanism are followed at a 2D coronal mass ejection-driven shock where the shock geometry varies across the shock front. The subsequent transport of energetic particles, including cross-field diffusion, is modeled by a Monte Carlo code that is based on a stochastic differential equation method. Time intensity profiles and particle spectra at multiple locations and different radial distances, separated in longitudes, are presented. The results shown here are relevant to the upcoming Parker Solar Probe mission.

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Date: 02/2018 Publisher: The Astrophysical Journal Pages: L19 DOI: 10.3847/2041-8213/aaabc1 Available at: http://stacks.iop.org/2041-8205/854/i=2/a=L19?key=crossref.3db06d37bee0fc065cdec82f4faaf3b7
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Authors: Winslow Reka M., Schwadron Nathan A., Lugaz é, Guo Jingnan, Joyce Colin J., et al.
Title: Opening a Window on ICME-driven GCR Modulation in the Inner Solar System
Abstract:

Interplanetary coronal mass ejections (ICMEs) often cause Forbush decreases (Fds) in the flux of galactic cosmic rays (GCRs). We investigate how a single ICME, launched from the Sun on 2014 February 12, affected GCR fluxes at Mercury, Earth, and Mars. We use GCR observations from MESSENGER at Mercury, ACE/LRO at the Earth/Moon, and MSL at Mars. We find that Fds are steeper and deeper closer to the Sun, and that the magnitude of the magnetic field in the ICME magnetic ejecta as well as the “strength” of the ICME sheath both play a large role in modulating the depth of the Fd. Based on our results, we hypothesize that (1) the Fd size decreases exponentially with heliocentric distance, and (2) that two-step Fds are more common closer to the Sun. Both hypotheses will be directly verifia. . .
Date: 04/2018 Publisher: The Astrophysical Journal Pages: 139 DOI: 10.3847/1538-4357/aab098 Available at: http://stacks.iop.org/0004-637X/856/i=2/a=139?key=crossref.287f3cbc519cdfae455bd8b9d0a9351a
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Authors: Xiong Ming, Davies Jackie A., Feng Xueshang, Li Bo, Yang Liping, et al.
Title: Prospective White-light Imaging and In Situ Measurements of Quiescent Large-scale Solar-wind Streams from the Parker Solar Probe and Solar Orbiter
Abstract:

Deep-space exploration of the inner heliosphere is in an unprecedented golden age, with the recent and forthcoming launches of the Parker Solar Probe (PSP) and Solar Orbiter (SolO) missions, respectively. In order to both predict and understand the prospective observations by PSP and SolO, we perform forward MHD modeling of the 3D inner heliosphere at solar minimum, and synthesize the white-light (WL) emission that would result from Thomson scattering of sunlight from the coronal and heliospheric plasmas. Both solar rotation and spacecraft trajectory should be considered when reconstructing quiescent large-scale solar-wind streams from PSP and SolO WL observations. When transformed from a static coordinate system into a corotating one, the elliptical orbit of PSP becomes a multiwinding . . .
Date: 12/2018 Publisher: The Astrophysical Journal Pages: 137 DOI: 10.3847/1538-4357/aae978 Available at: http://stacks.iop.org/0004-637X/868/i=2/a=137?key=crossref.fe473eb9a278d1ea105f9203808e2eab
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Authors: Perrone Denise, Stansby D, Horbury T, and Matteini L
Title: Radial evolution of the solar wind in pure high-speed streams: HELIOS revised observations
Abstract:

Spacecraft observations have shown that the proton temperature in the solar wind falls off with radial distance more slowly than expected for an adiabatic prediction. Usually, previous studies have been focused on the evolution of the solar-wind plasma by using the bulk speed as an order parameter to discriminate different regimes. In contrast, here, we study the radial evolution of pure and homogeneous fast streams (i.e. well-defined streams of coronal-hole plasma that maintain their identity during several solar rotations) by means of re-processed particle data, from the HELIOS satellites between 0.3 and 1 au. We have identified 16 intervals of unperturbed high-speed coronal-hole plasma, from three different sources and measured at different radial distances. The observations show tha. . .
Date: 10/2018 Publisher: Monthly Notices of the Royal Astronomical Society DOI: 10.1093/mnras/sty3348 Available at: https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/sty3348/5237719http://academic.oup.com/mnras/advance-article-pdf/doi/10.1093/mnras/sty3348/27082965/sty3348.pdf
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Authors: Perrone Denise, Stansby D, Horbury T S, and Matteini L
Title: Radial evolution of the solar wind in pure high-speed streams: HELIOS revised observations
Abstract:

Spacecraft observations have shown that the proton temperature in the solar wind falls off with radial distance more slowly than expected for an adiabatic prediction. Usually, previous studies have been focused on the evolution of the solar-wind plasma by using the bulk speed as an order parameter to discriminate different regimes. In contrast, here, we study the radial evolution of pure and homogeneous fast streams (i.e. well-defined streams of coronal-hole plasma that maintain their identity during several solar rotations) by means of re-processed particle data, from the HELIOS satellites between 0.3 and 1 au. We have identified 16 intervals of unperturbed high-speed coronal-hole plasma, from three different sources and measured at different radial distances. The observations show tha. . .
Date: 03/2019 Publisher: Monthly Notices of the Royal Astronomical Society Pages: 3730 - 3737 DOI: 10.1093/mnras/sty3348 Available at: https://academic.oup.com/mnras/article/483/3/3730/5237719http://academic.oup.com/mnras/article-pdf/483/3/3730/27299782/sty3348.pdf
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Authors: Roberts Merrill A, Uritsky Vadim M, DeVore Richard, and Karpen Judith T
Title: Simulated Encounters of the Parker Solar Probe with a Coronal-hole Jet
Abstract:

Solar coronal jets are small, transient, collimated ejections most easily observed in coronal holes (CHs). The upcoming Parker Solar Probe (PSP) mission provides the first opportunity to encounter CH jets in situ near the Sun and examine their internal structure and dynamics. Using projected mission orbital parameters, we have simulated PSP encounters with a fully three-dimensional magnetohydrodynamic (MHD) model of a CH jet. We find that three internal jet regions, featuring different wave modes and levels of compressibility, have distinct identifying signatures detectable by PSP. The leading Alfvén wave front and its immediate wake are characterized by trans-Alfvénic plasma flows with mild density enhancements. This front exhibits characteristics of a fast switch-on MHD shock, whose. . .
Date: 10/2018 Publisher: The Astrophysical Journal Pages: 14 DOI: 10.3847/1538-4357/aadb41 Available at: http://stacks.iop.org/0004-637X/866/i=1/a=14?key=crossref.839142d08cc9d207f0bd8fb8e2b59c4a
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Authors: Venzmer M. S., and Bothmer V.
Title: Solar-wind predictions for the Parker Solar Probeorbit
Abstract:

Context. The Parker Solar Probe (PSP; formerly Solar Probe Plus) mission will be humanitys first in situ exploration of the solar corona with closest perihelia at 9.86 solar radii (R) distance to the Sun. It will help answer hitherto unresolved questions on the heating of the solar corona and the source and acceleration of the solar wind and solar energetic particles. The scope of this study is to model the solar-wind environment for PSPs unprecedented distances in its prime mission phase during the years 2018 to 2025. The study is performed within the Coronagraphic German And US SolarProbePlus Survey (CGAUSS) which is the German contribution to the PSP mission as part of the Wide-field Imager for Solar PRobe. Aim. We present an empirical solar-wind model for the inner hel. . .
Date: 03/2018 Publisher: Astronomy & Astrophysics Pages: A36 DOI: 10.1051/0004-6361/201731831 Available at: https://www.aanda.org/10.1051/0004-6361/201731831https://www.aanda.org/10.1051/0004-6361/201731831/pdf
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Authors: Jeffrey Natasha L. S., Hahn Michael, Savin Daniel W., and Fletcher Lyndsay
Title: Spectroscopic Measurements of the Ion Velocity Distribution at the Base of the Fast Solar Wind
Abstract:

In situ measurements of the fast solar wind reveal non-thermal distributions of electrons, protons, and minor ions extending from 0.3 au to the heliopause. The physical mechanisms responsible for these non-thermal properties and the location where these properties originate remain open questions. Here, we present spectroscopic evidence, from extreme ultraviolet spectroscopy, that the velocity distribution functions (VDFs) of minor ions are already non-Gaussian at the base of the fast solar wind in a coronal hole, at altitudes of <1.1 R . Analysis of Fe, Si, and Mg spectral lines reveals a peaked line-shape core and broad wings that can be characterized by a kappa VDF. A kappa distribution fit gives very small kappa indices off-limb of κ ≈ 1.9-2.5, indicating either (. . .
Date: 03/2018 Publisher: The Astrophysical Journal Pages: L13 DOI: 10.3847/2041-8213/aab08c Available at: http://stacks.iop.org/2041-8205/855/i=1/a=L13?key=crossref.c49731858480faecf31502cc56e0b5f3
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2017
Authors: Reid Hamish A. S., and Kontar Eduard P.
Title: Langmuir wave electric fields induced by electron beams in the heliosphere
Abstract:

Solar electron beams responsible for type III radio emission generate Langmuir waves as they propagate out from the Sun. The Langmuir waves are observed via in situ electric field measurements. These Langmuir waves are not smoothly distributed but occur in discrete clumps, commonly attributed to the turbulent nature of the solar wind electron density. Exactly how the density turbulence modulates the Langmuir wave electric fields is understood only qualitatively. Using weak turbulence simulations, we investigate how solar wind density turbulence changes the probability distribution functions, mean value and variance of the beam-driven electric field distributions. Simulations show rather complicated forms of the distribution that are dependent upon how the electric fields are sampled. Ge. . .
Date: 02/2017 Publisher: Astronomy & Astrophysics Pages: A44 DOI: 10.1051/0004-6361/201629697 Available at: http://www.aanda.org/10.1051/0004-6361/201629697http://www.aanda.org/10.1051/0004-6361/201629697/pdf
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2015
Authors: Good S. W., Forsyth R. J., Raines J. M., Gershman D. J., Slavin J. A., et al.
Title: RADIAL EVOLUTION OF A MAGNETIC CLOUD: MESSENGER , STEREO , AND VENUS EXPRESS OBSERVATIONS
Abstract:

The Solar Orbiter and Solar Probe Plus missions will provide observations of magnetic clouds closer to the Sun than ever before, and it will be good preparation for these missions to make full use of the most recent in situ data sets from the inner heliosphere—namely, those provided by MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) and Venus Express—for magnetic cloud studies. We present observations of the same magnetic cloud made by MESSENGER at Mercury and later by Solar TErrestrial RElations Observatory-B (STEREO-B), while the spacecraft were radially aligned in 2011 November. Few such radial observations of magnetic clouds have been previously reported. Estimates of the solar wind speed at MESSENGER are also presented, calculated through the applicati. . .
Date: 07/2015 Publisher: The Astrophysical Journal Pages: 177 DOI: 10.1088/0004-637X/807/2/177 Available at: http://stacks.iop.org/0004-637X/807/i=2/a=177?key=crossref.a1b49ae2196cca72b5d1ec280eba0793
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2011
Authors: Velli Marco, Lionello Roberto, Linker Jon A., and ć Zoran
Title: CORONAL PLUMES IN THE FAST SOLAR WIND
Abstract:

The expansion of a coronal hole filled with a discrete number of higher density coronal plumes is simulated using a time-dependent two-dimensional code. A solar wind model including an exponential coronal heating function and a flux of Alfvén waves propagating both inside and outside the structures is taken as a basic state. Different plasma plume profiles are obtained by using different scale heights for the heating rates. Remote sensing and solar wind in situ observations are used to constrain the parameter range of the study. Time dependence due to plume ignition and disappearance is also discussed. Velocity differences of the order of ~50 km s-1, such as those found in microstreams in the high-speed solar wind, may be easily explained by slightly different heat depositio. . .
Date: 07/2011 Publisher: The Astrophysical Journal Pages: 32 DOI: 10.1088/0004-637X/736/1/32 Available at: http://stacks.iop.org/0004-637X/736/i=1/a=32?key=crossref.9f21641f557225a36ce23f05fa1256f6http://stacks.iop.org/0004-637X/736/i=1/a=32/pdf
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