Found 27 results
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Filters: Keyword is Astrophysics - Solar and Stellar Astrophysics  [Clear All Filters]
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: Al-Haddad Nada, Lugaz Noé, Poedts Stefaan, Farrugia Charles J., Nieves-Chinchilla Teresa, et al.
Title: Evolution of Coronal Mass Ejection Properties in the Inner Heliosphere: Prediction for the Solar Orbiter and Parker Solar Probe
Abstract:

The evolution of the magnetic field and plasma quantities inside a coronal mass ejection (CME) with distance are known from statistical studies using data from 1 au monitors, planetary missions, Helios, and Ulysses. This does not cover the innermost heliosphere, below 0.29 au, where no data are yet publicly available. Here, we describe the evolution of the properties of simulated CMEs in the inner heliosphere using two different initiation mechanisms. We compare the radial evolution of these properties with that found from statistical studies based on observations in the inner heliosphere by Helios and MESSENGER. We find that the evolution of the radial size and magnetic field strength is nearly indistinguishable for twisted flux rope from that of writhed CMEs. The evolution of these pr. . .
Date: 10/2019 Publisher: The Astrophysical Journal Pages: 179 DOI: 10.3847/1538-4357/ab4126 Available at: https://iopscience.iop.org/article/10.3847/1538-4357/ab4126
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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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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: 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: Chandran Benjamin D. G.
Title: Parametric instability, inverse cascade and the  range of solar-wind turbulence
Abstract:

In this paper, weak-turbulence theory is used to investigate the nonlinear evolution of the parametric instability in three-dimensional low-β plasmas at wavelengths much greater than the ion inertial length under the assumption that slow magnetosonic waves are strongly damped. It is shown analytically that the parametric instability leads to an inverse cascade of Alfvén wave quanta, and several exact solutions to the wave kinetic equations are presented. The main results of the paper concern the parametric decay of Alfvén waves that initially satisfy e+ ≫ e-, where e+ and e- are the frequency (f) spectra of Alfvén waves propagating in opposite directions along the magnetic field lines. If e+ initially has a peak frequency fDate: 02/2018 Publisher: Journal of Plasma Physics DOI: 10.1017/S0022377818000016 Available at: https://www.cambridge.org/core/product/identifier/S0022377818000016/type/journal_article
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Authors: Milligan Ryan O., and Ireland Jack
Title: On the Performance of Multi-Instrument Solar Flare Observations During Solar Cycle 24
Abstract:

The current fleet of space-based solar observatories offers us a wealth of opportunities to study solar flares over a range of wavelengths. Significant advances in our understanding of flare physics often come from coordinated observations between multiple instruments. Consequently, considerable efforts have been, and continue to be, made to coordinate observations among instruments ( e.g. through the Max Millennium Program of Solar Flare Research). However, there has been no study to date that quantifies how many flares have been observed by combinations of various instruments. Here we describe a technique that retrospectively searches archival databases for flares jointly observed by the Ramaty High Energy Solar Spectroscopic Imager (RHESSI), Solar Dynamics Observatory (SDO)/ EUV Vari. . .
Date: 02/2018 Publisher: Solar Physics DOI: 10.1007/s11207-017-1233-x Available at: http://link.springer.com/10.1007/s11207-017-1233-xhttp://link.springer.com/content/pdf/10.1007/s11207-017-1233-x.pdfhttp://link.springer.com/article/10.1007/s11207-017-1233-x/fulltext.htmlhttp://link.springer.com/content/pdf/10.1007/s11207-017-1233-x.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: 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: Raza Nayyer, Van Waerbeke Ludovic, and Zhitnitsky Ariel
Title: Solar corona heating by axion quark nugget dark matter
Abstract:

In this work we advocate for the idea that two seemingly unrelated 80-year-old mysteries—the nature of dark matter and the high temperature of the million degree solar corona—may have resolutions that lie within the same physical framework. The current paradigm is that the corona is heated by nanoflares, which were originally proposed as miniature versions of the observed solar flares. It was recently suggested that the nanoflares could be identified as annihilation events of the nuggets from the axion quark nugget (AQN) dark matter model. This model was invented as an explanation of the observed ratio Ωdark̃Ωvisible, based only on cosmological and particle physics considerations. In this new paradigm, the AQN particles moving through the coronal plasma and . . .
Date: 11/2018 Publisher: Physical Review D DOI: 10.1103/PhysRevD.98.103527 Available at: http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevD.98.103527/fulltext
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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: Kong Xiangliang, Guo Fan, Giacalone Joe, Li Hui, and Chen Yao
Title: The Acceleration of High-energy Protons at Coronal Shocks: The Effect of Large-scale Streamer-like Magnetic Field Structures
Abstract:

Recent observations have shown that coronal shocks driven by coronal mass ejections can develop and accelerate particles within several solar radii in large solar energetic particle (SEP) events. Motivated by this, we present an SEP acceleration study that including the process in which a fast shock propagates through a streamer-like magnetic field with both closed and open field lines in the low corona region. The acceleration of protons is modeled by numerically solving the Parker transport equation with spatial diffusion both along and across the magnetic field. We show that particles can be sufficiently accelerated to up to several hundred MeV within 2-3 solar radii. When the shock propagates through a streamer-like magnetic field, particles are more efficiently accelerated compared. . .
Date: 12/2017 Publisher: The Astrophysical Journal Pages: 38 DOI: 10.3847/1538-4357/aa97d7 Available at: http://stacks.iop.org/0004-637X/851/i=1/a=38?key=crossref.2009ec10fbd1f6f8cd1462070076984f
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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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Authors: Kasper J. C., Klein K. G., Weber T., Maksimovic M., Zaslavsky A., et al.
Title: A Zone of Preferential Ion Heating Extends Tens of Solar Radii from the Sun
Abstract:

The extreme temperatures and nonthermal nature of the solar corona and solar wind arise from an unidentified physical mechanism that preferentially heats certain ion species relative to others. Spectroscopic indicators of unequal temperatures commence within a fraction of a solar radius above the surface of the Sun, but the outer reach of this mechanism has yet to be determined. Here we present an empirical procedure for combining interplanetary solar wind measurements and a modeled energy equation including Coulomb relaxation to solve for the typical outer boundary of this zone of preferential heating. Applied to two decades of observations by the Wind spacecraft, our results are consistent with preferential heating being active in a zone extending from the transition region in the low. . .
Date: 11/2017 Publisher: The Astrophysical Journal Pages: 126 DOI: 10.3847/1538-4357/aa84b1 Available at: http://stacks.iop.org/0004-637X/849/i=2/a=126?key=crossref.a4fda357a12d19fd2ad1aa8a3897c78f
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2016
Authors: Klein Kristopher G., and Chandran Benjamin D. G.
Title: EVOLUTION OF THE PROTON VELOCITY DISTRIBUTION DUE TO STOCHASTIC HEATING IN THE NEAR-SUN SOLAR WIND
Abstract:

We investigate how the proton distribution function evolves when the protons undergo stochastic heating by strong, low-frequency, Alfvén-wave turbulence under the assumption that β is small. We apply our analysis to protons undergoing stochastic heating in the supersonic fast solar wind and obtain proton distributions at heliocentric distances ranging from 4 to 30 solar radii. We find that the proton distribution develops non-Gaussian structure with a flat core and steep tail. For r\gt 5 {R}{{S}}, the proton distribution is well approximated by a modified Moyal distribution. Comparisons with future measurements from Solar Probe Plus could be used to test whether stochastic heating is occurring in the solar-wind acceleration region.


Date: 03/2016 Publisher: The Astrophysical Journal Pages: 47 DOI: 10.3847/0004-637X/820/1/47 Available at: http://stacks.iop.org/0004-637X/820/i=1/a=47?key=crossref.3bba6a0e184137847bf77cde72a2fe1fhttp://stacks.iop.org/0004-637X/820/i=1/a=47/pdfhttp://stacks.iop.org/0004-637X/820/i=1/a=47?key=crossref.3bba6a0e184137847bf77cde72a2fe1f
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Authors: Klein K. G., and Howes G. G.
Title: MEASURING COLLISIONLESS DAMPING IN HELIOSPHERIC PLASMAS USING FIELD–PARTICLE CORRELATIONS
Abstract:

An innovative field-particle correlation technique is proposed that uses single-point measurements of the electromagnetic fields and particle velocity distribution functions to investigate the net transfer of energy from fields to particles associated with the collisionless damping of turbulent fluctuations in weakly collisional plasmas, such as the solar wind. In addition to providing a direct estimate of the local rate of energy transfer between fields and particles, it provides vital new information about the distribution of that energy transfer in velocity space. This velocity-space signature can potentially be used to identify the dominant collisionless mechanism responsible for the damping of turbulent fluctuations in the solar wind. The application of this novel field-particle co. . .
Date: 08/2016 Publisher: The Astrophysical Journal Pages: L30 DOI: 10.3847/2041-8205/826/2/L30 Available at: http://stacks.iop.org/2041-8205/826/i=2/a=L30?key=crossref.1f33350dac6f20e78faa0a9e9d852985http://stacks.iop.org/2041-8205/826/i=2/a=L30/pdfhttp://stacks.iop.org/2041-8205/826/i=2/a=L30?key=crossref.1f33350dac6f20e78faa0a9e9d852985
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Authors: Cranmer Steven R.
Title: Predictions for Dusty Mass Loss from Asteroids During Close Encounters with Solar Probe Plus
Abstract:

The Solar Probe Plus ( SPP) mission will explore the Sun's corona and innermost solar wind starting in 2018. The spacecraft will also come close to a number of Mercury-crossing asteroids with perihelia less than 0.3 AU. At small heliocentric distances, these objects may begin to lose mass, thus becoming "active asteroids" with comet-like comae or tails. This paper assembles a database of 97 known Mercury-crossing asteroids that may be encountered by SPP, and it presents estimates of their time-dependent visible-light fluxes and mass loss rates. Assuming a similar efficiency of sky background subtraction as was achieved by STEREO , we find that approximately 80 % of these asteroids are bright enough to be observed by the Wide-field Imager for SPP (WISPR). A model of gas/dust mass loss fr. . .
Date: 11/2016 Publisher: Earth, Moon, and Planets Pages: 51 - 79 DOI: 10.1007/s11038-016-9490-5 Available at: http://link.springer.com/10.1007/s11038-016-9490-5http://link.springer.com/content/pdf/10.1007/s11038-016-9490-5.pdfhttp://link.springer.com/content/pdf/10.1007/s11038-016-9490-5.pdfhttp://link.springer.com/article/10.1007/s11038-016-9490-5/fulltext.html
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2015
Authors: de Patoul Judith, Foullon Claire, and Riley Pete
Title: 3D ELECTRON DENSITY DISTRIBUTIONS IN THE SOLAR CORONA DURING SOLAR MINIMA: ASSESSMENT FOR MORE REALISTIC SOLAR WIND MODELING
Abstract:

Knowledge of the electron density distribution in the solar corona put constraints on the magnetic field configurations for coronal modeling and on initial conditions for solar wind modeling. We work with polarized SOHO/LASCO-C2 images from the last two recent minima of solar activity (1996-1997 and 2008-2010), devoid of coronal mass ejections. The goals are to derive the 4D electron density distributions in the corona by applying a newly developed time-dependent tomographic reconstruction method and to compare the results between the two solar minima and with two magnetohydrodynamic models. First, we confirm that the values of the density distribution in thermodynamic models are more realistic than in polytropic ones. The tomography provides more accurate distributions in the polar reg. . .
Date: 11/2015 Publisher: The Astrophysical Journal Pages: 68 DOI: 10.1088/0004-637X/814/1/68 Available at: http://stacks.iop.org/0004-637X/814/i=1/a=68?key=crossref.845557cfda4b2a3786588c8b62dbb093
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Authors: Klein Kristopher G., Perez Jean C., Verscharen Daniel, Mallet Alfred, and Chandran Benjamin D. G.
Title: A MODIFIED VERSION OF TAYLOR’S HYPOTHESIS FOR SOLAR PROBE PLUS OBSERVATIONS
Abstract:

The Solar Probe Plus (SPP) spacecraft will explore the near-Sun environment, reaching heliocentric distances less than 10 {{R}}. Near Earth, spacecraft measurements of fluctuating velocities and magnetic fields taken in the time domain are translated into information about the spatial structure of the solar wind via Taylor’s “frozen turbulence” hypothesis. Near the perihelion of SPP, however, the solar-wind speed is comparable to the Alfvén speed, and Taylor’s hypothesis in its usual form does not apply. In this paper, we show that under certain assumptions, a modified version of Taylor’s hypothesis can be recovered in the near-Sun region. We consider only the transverse, non-compressive component of the fluctuations at length scales exceeding the proton gyrora. . .
Date: 03/2015 Publisher: The Astrophysical Journal Pages: L18 DOI: 10.1088/2041-8205/801/1/L18 Available at: http://stacks.iop.org/2041-8205/801/i=1/a=L18?key=crossref.c92a2bde23ce9cdd58185dec581d5a09
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2014
Authors: Li T. C., Drake J. F., and Swisdak M.
Title: DYNAMICS OF DOUBLE LAYERS, ION ACCELERATION, AND HEAT FLUX SUPPRESSION DURING SOLAR FLARES
Abstract:

Observations of flare-heated electrons in the corona typically suggest confinement of electrons. The confinement mechanism, however, remains unclear. The transport of coronal hot electrons into ambient plasma was recently investigated by particle-in-cell (PIC) simulations. Electron transport was significantly suppressed by the formation of a highly localized, nonlinear electrostatic potential in the form of a double layer (DL). In this work large-scale PIC simulations are performed to explore the dynamics of DLs in larger systems where, instead of a single DL, multiple DLs are generated. The primary DL accelerates return current electrons, resulting in high velocity electron beams that interact with ambient ions. This forms a Buneman unstable system that spawns more DLs. Trapping of hea. . .
Date: 09/2014 Publisher: The Astrophysical Journal Pages: 7 DOI: 10.1088/0004-637X/793/1/7 Available at: http://stacks.iop.org/0004-637X/793/i=1/a=7?key=crossref.1ff276d1b5e9632b2d52ebb5720bc5e6
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Authors: DeForest C. E., Howard T. A., and McComas D. J.
Title: INBOUND WAVES IN THE SOLAR CORONA: A DIRECT INDICATOR OF ALFVÉN SURFACE LOCATION
Abstract:

The tenuous supersonic solar wind that streams from the top of the corona passes through a natural boundary—the Alfvén surface—that marks the causal disconnection of individual packets of plasma and magnetic flux from the Sun itself. The Alfvén surface is the locus where the radial motion of the accelerating solar wind passes the radial Alfvén speed, and therefore any displacement of material cannot carry information back down into the corona. It is thus the natural outer boundary of the solar corona and the inner boundary of interplanetary space. Using a new and unique motion analysis to separate inbound and outbound motions in synoptic visible-light image sequences from the COR2 coronagraph on board the STEREO-A spacecraft, we have identified inbound wave motion in the outer co. . .
Date: 06/2014 Publisher: The Astrophysical Journal Pages: 124 DOI: 10.1088/0004-637X/787/2/124 Available at: http://stacks.iop.org/0004-637X/787/i=2/a=124?key=crossref.8ca79a982204ddd2b4922cc108364616
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Authors: Howes G. G., Klein K. G., and TenBarge J. M.
Title: VALIDITY OF THE TAYLOR HYPOTHESIS FOR LINEAR KINETIC WAVES IN THE WEAKLY COLLISIONAL SOLAR WIND
Abstract:

The interpretation of single-point spacecraft measurements of solar wind turbulence is complicated by the fact that the measurements are made in a frame of reference in relative motion with respect to the turbulent plasma. The Taylor hypothesis—that temporal fluctuations measured by a stationary probe in a rapidly flowing fluid are dominated by the advection of spatial structures in the fluid rest frame—is often assumed to simplify the analysis. But measurements of turbulence in upcoming missions, such as Solar Probe Plus, threaten to violate the Taylor hypothesis, either due to slow flow of the plasma with respect to the spacecraft or to the dispersive nature of the plasma fluctuations at small scales. Assuming that the frequency of the turbulent fluctuations is characterized by th. . .
Date: 07/2014 Publisher: The Astrophysical Journal Pages: 106 DOI: 10.1088/0004-637X/789/2/106 Available at: http://stacks.iop.org/0004-637X/789/i=2/a=106?key=crossref.25a7683ba86c87973ee983db364c5e6f
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