Found 115 results
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Journal Article
Authors: Yoon P. H., Seough J., Salem C. S., and Klein K. G.
Title: Solar Wind Temperature Isotropy
Abstract:

Reliable models of the solar wind in the near-Earth space environment may constrain conditions close to the Sun. This is relevant to NASA's contemporary innerheliospheric mission Parker Solar Probe. Among the outstanding issues is how to explain the solar wind temperature isotropy. Perpendicular and parallel proton and electron temperatures near 1 AU are theoretically predicted to be unequal, but in situ observations show quasi-isotropy sufficiently below the instability threshold condition. This has not been satisfactorily explained. The present Letter shows that the dynamical coupling of electrons and protons via collisional processes and instabilities may contribute toward the resolution of this problem.


Date: 10/2019 Publisher: Physical Review Letters DOI: 10.1103/PhysRevLett.123.145101 Available at: https://link.aps.org/doi/10.1103/PhysRevLett.123.145101http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevLett.123.145101/fulltexthttps://link.aps.org/article/10.1103/PhysRevLett.123.145101
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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: Ergun R. E., Malaspina D. M., Bale S. D., McFadden J. P., Larson D. E., et al.
Title: Spacecraft charging and ion wake formation in the near-Sun environment
Abstract:

A three-dimensional, self-consistent code is employed to solve for the static potential structure surrounding a spacecraft in a high photoelectron environment. The numerical solutions show that, under certain conditions, a spacecraft can take on a negative potential in spite of strong photoelectron currents. The negative potential is due to an electrostatic barrier near the surface of the spacecraft that can reflect a large fraction of the photoelectron flux back to the spacecraft. This electrostatic barrier forms if (1) the photoelectron density at the surface of the spacecraft greatly exceeds the ambient plasma density, (2) the spacecraft size is significantly larger than local Debye length of the photoelectrons, and (3) the thermal electron energy is much larger than the characterist. . .
Date: 07/2010 Publisher: Physics of Plasmas Pages: 072903 DOI: 10.1063/1.3457484 Available at: http://aip.scitation.org/doi/10.1063/1.3457484http://aip.scitation.org/doi/pdf/10.1063/1.3457484
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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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Authors: Ruffenach A., Lavraud B., Farrugia C. J., émoulin P., Dasso S., et al.
Title: Statistical study of magnetic cloud erosion by magnetic reconnection
Abstract:

recent studies suggest that magnetic reconnection is able to erode substantial amounts of the outer magnetic flux of interplanetary magnetic clouds (MCs) as they propagate in the heliosphere. We quantify and provide a broader context to this process, starting from 263 tabulated interplanetary coronal mass ejections, including MCs, observed over a time period covering 17 years and at a distance of 1 AU from the Sun with Wind (1995-2008) and the two STEREO (2009-2012) spacecraft. Based on several quality factors, including careful determination of the MC boundaries and main magnetic flux rope axes, an analysis of the azimuthal flux imbalance expected from erosion by magnetic reconnection was performed on a subset of 50 MCs. The results suggest that MCs may be eroded at the front or at rea. . .
Date: 01/2015 Publisher: Journal of Geophysical Research: Space Physics Pages: 43 - 60 DOI: 10.1002/2014JA020628 Available at: http://doi.wiley.com/10.1002/2014JA020628http://onlinelibrary.wiley.com/wol1/doi/10.1002/2014JA020628/fullpdf
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Authors: Plus R., and Lutz M.
Title: Study of Band IV of Porphin by Resonance Raman Spectroscopy
Abstract:

Excitation spectra were obtained for 21 resonance Raman bands of porphin from 455 to 515 nm. Each of them exhibited one to three maxima which generally lay close to 453, 475 and 490 nm. These three resonance levels were tentatively attributed to the presence of pure electronic transitions in band IV. The few other maxima could be interpreted as resonance at vibrational sublevels of band III. The structure of band IV is thus shown to be of greater complexity than has been generally suspected up to now.


Date: 01/1974 Publisher: Spectroscopy Letters Pages: 73 - 84 DOI: 10.1080/00387017408067222 Available at: http://www.tandfonline.com/doi/abs/10.1080/00387017408067222http://www.tandfonline.com/doi/pdf/10.1080/00387017408067222
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Authors: Witze Alexandra
Title: Sun-bombing spacecraft uncovers secrets of the solar wind
Abstract:

Surprise magnetic reversals and an unexpectedly fast rotating wind mark the first findings from NASA's Parker Solar Probe.


Date: 12/2019 Publisher: Nature Pages: 15 - 16 DOI: 10.1038/d41586-019-03684-0 Available at: http://www.nature.com/articles/d41586-019-03684-0http://www.nature.com/articles/d41586-019-03684-0.pdfhttp://www.nature.com/articles/d41586-019-03684-0.pdfhttp://www.nature.com/articles/d41586-019-03684-0
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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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Authors: Plus R.
Title: Utilisation des isotopes D, 15N, 26Mg pour l'étude vibrationnelle de Mg(NH3)6Cl2.
Abstract:

The following substituted magnesium chloride hexa-ammines: 24Mg( 14NH 3) 6Cl 2; 26Mg( 14NH 3) 6Cl 2; 24Mg( 15NH 3) 6Cl 2; 24Mg( 14ND 3) 6Cl 2; 24Mg( 14ND 3) 6Cl 2 have been studied by i.r. and Raman spectroscopy. The frequency shifts have been measured for all active vibrational bands predicted by group theory analysis. The results show that measurements made on isotopically substituted compounds can provide confirmation of assignments of vibrational bands previously proposed [2].


Date: 01/1976 Publisher: Spectrochimica Acta Part A: Molecular Spectroscopy Pages: 263 - 268 DOI: 10.1016/0584-8539(76)80076-1 Available at: http://linkinghub.elsevier.com/retrieve/pii/0584853976800761http://api.elsevier.com/content/article/PII:0584853976800761?httpAccept=text/xmlhttp://api.elsevier.com/content/article/PII:0584853976800761?httpAccept=text/plain
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Authors: Lamy Philippe, Floyd Olivier, Mikic Zoran, and Riley Pete
Title: Validation of MHD Model Predictions of the Corona with LASCO-C2 Polarized Brightness Images
Abstract:

Progress in our understanding of the solar corona requires that the results of advanced magnetohydrodynamic models driven by measured magnetic fields, and particularly the underlying heating models, be thoroughly compared with coronal observations. The comparison has so far mainly concerned the global morphology of the corona, synthetic images calculated from the models being compared with observed images. We go one step further by performing detailed quantitative comparisons between the calculated polarized radiance p B using the three-dimensional electron density produced by MHD models and well calibrated polarized images obtained by the Large Angle Spectrometric Coronagraph LASCO-C2 coronagraph complemented by ground-based images when available from the Mauna Loa Solar Observatory Ma. . .
Date: 11/2019 Publisher: Solar Physics DOI: 10.1007/s11207-019-1549-9 Available at: http://link.springer.com/10.1007/s11207-019-1549-9http://link.springer.com/content/pdf/10.1007/s11207-019-1549-9.pdfhttp://link.springer.com/content/pdf/10.1007/s11207-019-1549-9.pdfhttp://link.springer.com/article/10.1007/s11207-019-1549-9/fulltext.html
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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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Authors: Klein K. G., Howes G. G., and TenBarge J. M.
Title: THE VIOLATION OF THE TAYLOR HYPOTHESIS IN MEASUREMENTS OF SOLAR WIND TURBULENCE
Abstract:

Motivated by the upcoming Solar Orbiter and Solar Probe Plus missions, qualitative and quantitative predictions are made for the effects of the violation of the Taylor hypothesis on the magnetic energy frequency spectrum measured in the near-Sun environment. The synthetic spacecraft data method is used to predict observational signatures of the violation for critically balanced Alfvénic turbulence or parallel fast/whistler turbulence. The violation of the Taylor hypothesis can occur in the slow flow regime, leading to a shift of the entire spectrum to higher frequencies, or in the dispersive regime, in which the dissipation range spectrum flattens at high frequencies. It is found that Alfvénic turbulence will not significantly violate the Taylor hypothesis, but whistler turbulence wil. . .
Date: 08/2014 Publisher: The Astrophysical Journal Pages: L20 DOI: 10.1088/2041-8205/790/2/L20 Available at: http://stacks.iop.org/2041-8205/790/i=2/a=L20?key=crossref.9873bcfbec22617b78b4a7d0cb1dbb95
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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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