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2019
Authors: Chhiber Rohit, Usmanov Arcadi V., Matthaeus William H., and Goldstein Melvyn L.
Title: Contextual Predictions for the Parker Solar Probe . I. Critical Surfaces and Regions
Abstract:

The solar corona and young solar wind may be characterized by critical surfaces—the sonic, Alfvén, and first plasma-β unity surfaces—that demarcate regions where the solar wind flow undergoes certain crucial transformations. Global numerical simulations and remote sensing observations offer a natural mode for the study of these surfaces at large scales, thus providing valuable context for the high-resolution in situ measurements expected from the recently launched Parker Solar Probe (PSP). The present study utilizes global three-dimensional magnetohydrodynamic (MHD) simulations of the solar wind to characterize the critical surfaces and investigate the flow in propinquitous regions. Effects of solar activity are incorporated by varying source magnetic dipole tilts and employing ma. . .
Date: 03/2019 Publisher: The Astrophysical Journal Supplement Series Pages: 11 DOI: 10.3847/1538-4365/ab0652 Available at: http://stacks.iop.org/0067-0049/241/i=1/a=11?key=crossref.5e73dbbb501083f4d606cdf21e74f766http://stacks.iop.org/0067-0049/241/i=1/a=11/
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Authors: Telloni Daniele, Giordano Silvio, and Antonucci Ester
Title: On the Fast Solar Wind Heating and Acceleration Processes: A Statistical Study Based on the UVCS Survey Data
Abstract:

The UltraViolet Coronagraph Spectrometer (UVCS) on board the SOlar and Heliospheric Observatory has almost continuously observed, throughout the whole solar cycle 23, the UV solar corona. This work addresses the first-ever statistical analysis of the daily UVCS observations, performed in the O VI channel, of the northern polar coronal hole, between 1.5 and 3 R , during the period of low solar activity from 1996 April to 1997 December. The study is based on the investigation, at different heights, of the correlation between the variance of the O VI 1031.92 Å spectral line and the O VI 1031.92, 1037.61 Å doublet intensity ratio, which are proxies of the kinetic temperature of the O5+ ions and of the speed of the oxygen component of the fast solar wind, respectiv. . .
Date: 08/2019 Publisher: The Astrophysical Journal Pages: L36 DOI: 10.3847/2041-8213/ab3731 Available at: https://iopscience.iop.org/article/10.3847/2041-8213/ab3731
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Authors: Chang Qing, Xu Xiaojun, Xu Qi, Zhong Jun, Xu Jiaying, et al.
Title: Multiple-point Modeling the Parker Spiral Configuration of the Solar Wind Magnetic Field at the Solar Maximum of Solar Cycle 24
Abstract:

By assuming that the solar wind flow is spherically symmetric and that the flow speed becomes constant beyond some critical distance r = R 0 (neglecting solar gravitation and acceleration by high coronal temperature), the large-scale solar wind magnetic field lines are distorted into a Parker spiral configuration, which is usually simplified to an Archimedes spiral. Using magnetic field observations near Mercury, Venus, and Earth during solar maximum of Solar Cycle 24, we statistically surveyed the Parker spiral angles and obtained the empirical equations of the Archimedes and Parker spirals by fitting the multiple-point results. We found that the solar wind magnetic field configurations are slightly different during different years. Archimedes and Parker spiral configuration. . .
Date: 10/2019 Publisher: The Astrophysical Journal Pages: 102 DOI: 10.3847/1538-4357/ab412a Available at: https://iopscience.iop.org/article/10.3847/1538-4357/ab412
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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: Parashar T. N., Cuesta M., and Matthaeus W. H.
Title: Reynolds Number and Intermittency in the Expanding Solar Wind: Predictions Based on Voyager Observations
Abstract:

The large-scale features of the solar wind are examined in order to predict small-scale features of turbulence in unexplored regions of the heliosphere. The strategy is to examine how system size, or effective Reynolds number Re, varies, and then how this quantity influences observable statistical properties, including intermittency properties of solar wind turbulence. The expectation based on similar hydrodynamics scalings is that the kurtosis, of the small-scale magnetic field increments, will increase with increasing Re. Simple theoretical arguments as well as Voyager observations indicate that effective interplanetary turbulence Re decreases with increasing heliocentric distance. The decrease of scale-dependent magnetic increment kurtosis with increasing heliocentric distance is ver. . .
Date: 10/2019 Publisher: The Astrophysical Journal Pages: L57 DOI: 10.3847/2041-8213/ab4a82 Available at: https://iopscience.iop.org/article/10.3847/2041-8213/ab4a82
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Authors: Pecora Francesco, Greco Antonella, Hu Qiang, Servidio Sergio, Chasapis Alexandros G., et al.
Title: Single-spacecraft Identification of Flux Tubes and Current Sheets in the Solar Wind
Abstract:

A novel technique is presented for describing and visualizing the local topology of the magnetic field using single-spacecraft data in the solar wind. The approach merges two established techniques: the Grad─Shafranov (GS) reconstruction method, which provides a plausible regional two-dimensional magnetic field surrounding the spacecraft trajectory, and the Partial Variance of Increments (PVI) technique that identifies coherent magnetic structures, such as current sheets. When applied to one month of Wind magnetic field data at 1 minute resolution, we find that the quasi-two-dimensional turbulence emerges as a sea of magnetic islands and current sheets. Statistical analysis confirms that current sheets associated with high values of PVI are mostly located between and within the GS mag. . .
Date: 08/2019 Publisher: The Astrophysical Journal Pages: L11 DOI: 10.3847/2041-8213/ab32d9 Available at: https://iopscience.iop.org/article/10.3847/2041-8213/ab32d9
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Authors: Pavan J., and Viñas A. F.
Title: Temperature Fluctuation at the Sun and Large-scale Electric Field in Solar Wind: A Challenge for the Parker Solar Probe Mission
Abstract:

Velocity distributions of particles are key elements in the study of solar wind. The physical mechanisms that regulate their many features are a matter of debate. The present work addresses the subject with a fully analytical method in order to establish the shape of particle velocity distributions in solar wind. The method consists of solving the steady-state kinetic equation for particles and the related fluid equations, with spatial profiles for density and temperature that match general observational data. The model is one-dimensional in configuration-space and two-dimensional in velocity-space, and accounts for large-scale processes, namely, advection, gravity, magnetic mirroring, and the large-scale ambipolar electric field. The findings reported add to the general understanding o. . .
Date: 09/2019 Publisher: The Astrophysical Journal Pages: 28 DOI: 10.3847/1538-4357/ab2fcd
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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: Owens Mathew J., Lockwood Mike, Barnard Luke A., and MacNeil Allan R.
Title: Generation of Inverted Heliospheric Magnetic Flux by Coronal Loop Opening and Slow Solar Wind Release
Abstract:

In situ spacecraft observations provide much-needed constraints on theories of solar wind formation and release, particularly the highly variable slow solar wind, which dominates near-Earth space. Previous studies have shown an association between local inversions in the heliospheric magnetic field (HMF) and solar wind released from the vicinity of magnetically closed coronal structures. We here show that in situ properties of inverted HMF are consistent with the same hot coronal source regions as the slow solar wind. We propose that inverted HMF is produced by solar wind speed shear, which results from interchange reconnection between a coronal loop and open flux tube, and introduces a pattern of fast─slow─fast wind along a given HMF flux tube. This same loop-opening process is tho. . .
Date: 11/2018 Publisher: The Astrophysical Journal Pages: L14 DOI: 10.3847/2041-8213/aaee82 Available at: http://stacks.iop.org/2041-8205/868/i=1/a=L14?key=crossref.317335516eaf9fd091c127050a2fecdd
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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: Bourdin Philippe, Singh Nishant K., and Brandenburg Axel
Title: Magnetic Helicity Reversal in the Corona at Small Plasma Beta
Abstract:

Solar and stellar dynamos shed small-scale and large-scale magnetic helicity of opposite signs. However, solar wind observations and simulations have shown that some distance above the dynamo both the small-scale and large-scale magnetic helicities have reversed signs. With realistic simulations of the solar corona above an active region now being available, we have access to the magnetic field and current density along coronal loops. We show that a sign reversal in the horizontal averages of the magnetic helicity occurs when the local maximum of the plasma beta drops below unity and the field becomes nearly fully force free. Hence, this reversal is expected to occur well within the solar corona and would not directly be accessible to in situ measurements with the Parker Solar Probe or . . .
Date: 12/2018 Publisher: The Astrophysical Journal Pages: 2 DOI: 10.3847/1538-4357/aae97a Available at: http://stacks.iop.org/0004-637X/869/i=1/a=2?key=crossref.90fa7f41d90e2c8b57f8248c0437cc6b
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Authors: Stansby David, Salem Chadi, Matteini Lorenzo, and Horbury Timothy
Title: A New Inner Heliosphere Proton Parameter Dataset from the Helios Mission
Abstract:

In the near future, Parker Solar Probe and Solar Orbiter will provide the first comprehensive in-situ measurements of the solar wind in the inner heliosphere since the Helios mission in the 1970s. We describe a reprocessing of the original Helios ion distribution functions to provide reliable and reproducible data to characterise the proton core population of the solar wind in the inner heliosphere. A systematic fitting of bi-Maxwellian distribution functions was performed to the raw Helios ion distribution function data to extract the proton core number density, velocity, and temperatures parallel and perpendicular to the magnetic field. We present radial trends of these derived proton parameters, forming a benchmark to which new measurements in the inner heliosphere will be compared. . . .
Date: 11/2018 Publisher: Solar Physics DOI: 10.1007/s11207-018-1377-3 Available at: http://link.springer.com/10.1007/s11207-018-1377-3http://link.springer.com/content/pdf/10.1007/s11207-018-1377-3.pdfhttp://link.springer.com/article/10.1007/s11207-018-1377-3/fulltext.htmlhttp://link.springer.com/content/pdf/10.1007/s11207-018-1377-3.pdf
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Authors: éville Victor, Tenerani Anna, and Velli Marco
Title: Parametric Decay and the Origin of the Low-frequency Alfvénic Spectrum of the Solar Wind
Abstract:

The fast solar wind shows a wide spectrum of transverse magnetic and velocity field perturbations. These perturbations are strongly correlated in the sense of Alfvén waves propagating mostly outward, from the Sun to the interplanetary medium. They are likely to be fundamental to the acceleration and the heating of the solar wind. However, the precise origin of the broadband spectrum is unknown to date. Typical periods of chromospheric Alfvén waves are limited to a few minutes, and any longer period perturbations should be strongly reflected at the transition region. In this work, we show that minute long Alfvénic fluctuations are unstable to the parametric instability. Parametric instability enables an inverse energy cascade by exciting several-hour-long periods of Alfvénic fluctuat. . .
Date: 10/2018 Publisher: The Astrophysical Journal Pages: 38 DOI: 10.3847/1538-4357/aadb8f Available at: http://stacks.iop.org/0004-637X/866/i=1/a=38?key=crossref.877507b60fca8d8ddb73692a546936b0
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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: Horbury T S, Matteini L, and Stansby D
Title: Short, large-amplitude speed enhancements in the near-Sunfast solar wind
Abstract:

We report the presence of intermittent, short discrete enhancements in plasma speed in the near-Sun high-speed solar wind. Lasting tens of seconds to minutes in spacecraft measurements at 0.3 au, speeds inside these enhancements can reach 1000 km s-1, corresponding to a kinetic energy up to twice that of the bulk high-speed solar wind. These events, which occur around 5 per cent of the time, are Alfvénic in nature with large magnetic field deflections and are the same temperature as the surrounding plasma, in contrast to the bulk fast wind which has a well-established positive speed-temperature correlation. The origin of these speed enhancements is unclear but they may be signatures of discrete jets associated with transient events in the chromosphere or corona. Such large s. . .
Date: 08/2018 Publisher: Monthly Notices of the Royal Astronomical Society Pages: 1980 - 1986 DOI: 10.1093/mnras/sty953 Available at: https://academic.oup.com/mnras/article/478/2/1980/4987231
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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: Amicis Raffaella ’, Matteini Lorenzo, and Bruno Roberto
Title: On slow solar wind with high Alfvénicity: from composition and microphysics to spectral properties
Abstract:

Alfvénic fluctuations are very common features in the solar wind and are found especially within the main portion of fast-wind streams while the slow wind usually is less Alfvénic and more variable. In general, the fast and slow winds show many differences, which span from the large-scale structure to small-scale phenomena, including also a different turbulent behaviour. Recent studies, however, have shown that even the slow wind can sometimes be highly Alfvénic, with fluctuations as large as those of the fast wind. This study is devoted to presenting many facets of this Alfvénic slow solar wind, including for example the study of the source regions and their connection to coronal structures, large-scale properties, and microscale phenomena and also impact on the spectral features. . . .
Date: 3/2019 Publisher: Monthly Notices of the Royal Astronomical Society DOI: 10.1093/mnras/sty3329 Available at: https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/sty3329/5245187http://academic.oup.com/mnras/advance-article-pdf/doi/10.1093/mnras/sty3329/27125375/sty3329.pdf
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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: Reid Hamish A. S., and Kontar Eduard P.
Title: Spatial Expansion and Speeds of Type III Electron Beam Sources in the Solar Corona
Abstract:

A component of space weather, electron beams are routinely accelerated in the solar atmosphere and propagate through interplanetary space. Electron beams interact with Langmuir waves resulting in type III radio bursts. They expand along the trajectory and, using kinetic simulations, we explore the expansion as the electrons propagate away from the Sun. Specifically, we investigate the front, peak, and back of the electron beam in space from derived radio brightness temperatures of fundamental type III emission. The front of the electron beam travels at speeds from 0.2c to 0.7c, significantly faster than the back of the beam, which travels at speeds between 0.12c and 0.35c. The difference in speed between the front and the back elongates the electron beam in time. The rate of beam elonga. . .
Date: 11/2018 Publisher: The Astrophysical Journal Pages: 158 DOI: 10.3847/1538-4357/aae5d4 Available at: http://stacks.iop.org/0004-637X/867/i=2/a=158?key=crossref.0069d201e36ac912893a93028da80455
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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: Main Astronomical Observatory of the National Academy of Sciences of Ukraine, Kyiv, and Vasylenko A.A.
Title: Future space missions: the inner region of the Solar system
Abstract:

The paper deals with an overview of space missions to explore the inner region of the Solar System, the nearest on time of their launch, namely, Probe Plus, Solar Orbiter, BepiColombo, EXOMars, and InSight. Each of them will study either the Sun or the planet of the Earth group. Their launches are planned for 2018-2020. We describe briefly predestination and technical equipment of spacecrafts, flight plan and scientific goal of these missions.


Date: 10/2017 Publisher: Kosmìčna nauka ì tehnologìâ Pages: 73 - 80 DOI: 10.15407/knit10.15407/knit2017.0310.15407/knit2017.03.073 Available at: http://space-scitechjournal.org.ua/enhttp://space-scitechjournal.org.ua/en/archive/2017/3http://space-scitechjournal.org.ua/en/archive/2017/3/07
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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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Pages