Found 31 results
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Authors: Verscharen Daniel, Chandran Benjamin D. G., Jeong Seong-Yeop, Salem Chadi S., Pulupa Marc P., et al.
Title: Self-induced Scattering of Strahl Electrons in the Solar Wind

We investigate the scattering of strahl electrons by microinstabilities as a mechanism for creating the electron halo in the solar wind. We develop a mathematical framework for the description of electron-driven microinstabilities and discuss the associated physical mechanisms. We find that an instability of the oblique fast-magnetosonic/whistler (FM/W) mode is the best candidate for a microinstability that scatters strahl electrons into the halo. We derive approximate analytic expressions for the FM/W instability threshold in two different β c regimes, where β c is the ratio of the core electrons’ thermal pressure to the magnetic pressure, and confirm the accuracy of these thresholds through comparison with numerical solutions to the hot-plasma dispersion rela. . .
Date: 12/2019 Publisher: The Astrophysical Journal Pages: 136 DOI: 10.3847/1538-4357/ab4c30 Available at:
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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

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:
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Authors: Yoon P. H., Seough J., Salem C. S., and Klein K. G.
Title: Solar Wind Temperature Isotropy

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:
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Authors: Witze Alexandra
Title: Sun-bombing spacecraft uncovers secrets of the solar wind

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:
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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

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:
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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

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:
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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

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:
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Authors: Raza Nayyer, Van Waerbeke Ludovic, and Zhitnitsky Ariel
Title: Solar corona heating by axion quark nugget dark matter

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:
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Authors: Venzmer M. S., and Bothmer V.
Title: Solar-wind predictions for the Parker Solar Probeorbit

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:
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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

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:
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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

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:
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Authors: Pulupa M., Bale S. D., Bonnell J. W., Bowen T. A., Carruth N., et al.
Title: The solar probe plus radio frequency spectrometer: Measurement requirements, analog design, and digital signal processing

The Radio Frequency Spectrometer (RFS) is a two-channel digital receiver and spectrometer, which will make remote sensing observations of radio waves and in situ measurements of electrostatic and electromagnetic fluctuations in the solar wind. A part of the FIELDS suite for Solar Probe Plus (SPP), the RFS is optimized for measurements in the inner heliosphere, where solar radio bursts are more intense and the plasma frequency is higher compared to previous measurements at distances of 1 AU or greater. The inputs to the RFS receiver are the four electric antennas mounted near the front of the SPP spacecraft and a single axis of the SPP search coil magnetometer (SCM). Each RFS channel selects a monopole or dipole antenna input, or the SCM input, via multiplexers. The primary data products. . .
Date: 03/2017 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1002/2016JA023345 Available at:
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Authors: Abbo L., Ofman L., Antiochos S. K., Hansteen V. H., Harra L., et al.
Title: Slow Solar Wind: Observations and Modeling

While it is certain that the fast solar wind originates from coronal holes, where and how the slow solar wind (SSW) is formed remains an outstanding question in solar physics even in the post-SOHO era. The quest for the SSW origin forms a major objective for the planned future missions such as the Solar Orbiter and Solar Probe Plus. Nonetheless, results from spacecraft data, combined with theoretical modeling, have helped to investigate many aspects of the SSW. Fundamental physical properties of the coronal plasma have been derived from spectroscopic and imaging remote-sensing data and in situ data, and these results have provided crucial insights for a deeper understanding of the origin and acceleration of the SSW. Advanced models of the SSW in coronal streamers and other structures ha. . .
Date: 11/2016 Publisher: Space Science Reviews Pages: 55 - 108 DOI: 10.1007/s11214-016-0264-1 Available at:
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Authors: Schwadron N. A., Bastian T., Leibacher J., Gary D., Pevtsov A., et al.
Title: The Solar Probe Plus Ground Based Network

Executive Summary. The role of the Solar Probe Plus (SPP) Ground-Based Network

(SPP-GBN) is to optimize and enhance the science return of the SPP mission by

providing unique data from the ground. The role of the GBN extends to planning and

coordination, supported by appropriate infrastructure, to ensure that the right kinds of

observations are acquired by the various facilities (see below), at the right times, and that

the data are readily accessible to the community for a variety of uses. The SPP-GBN

addresses science questions that will help interpreting SPP data, but also provide global

context and allow us to understand how SPP observations inform our understanding of

solar phenomena. Specifically, the S. . .
Date: DOI: N/A Available at:
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Authors: Fox N. J., Velli M. C., Bale S. D., Decker R., Driesman A., et al.
Title: The Solar Probe Plus Mission: Humanity’s First Visit to Our Star

Solar Probe Plus (SPP) will be the first spacecraft to fly into the low solar corona. SPP's main science goal is to determine the structure and dynamics of the Sun's coronal magnetic field, understand how the solar corona and wind are heated and accelerated, and determine what processes accelerate energetic particles. Understanding these fundamental phenomena has been a top-priority science goal for over five decades, dating back to the 1958 Simpson Committee Report. The scale and concept of such a mission has been revised at intervals since that time, yet the core has always been a close encounter with the Sun. The mission design and the technology and engineering developments enable SPP to meet its science objectives to: (1) Trace the flow of energy that heats and accelerates the sola. . .
Date: 12/2016 Publisher: Space Science Reviews Pages: 7 - 48 DOI: 10.1007/s11214-015-0211-6 Available at:
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Authors: Chhiber R, Usmanov AV, Matthaeus WH, and Goldstein ML

Simple estimates of the number of Coulomb collisions experienced by the interplanetary plasma to the point of observation, I.e., the “collisional age”, can be usefully employed in the study of non-thermal features of the solar wind. Usually these estimates are based on local plasma properties at the point of observation. Here we improve the method of estimation of the collisional age by employing solutions obtained from global three-dimensional magnetohydrodynamics simulations. This enables evaluation of the complete analytical expression for the collisional age without using approximations. The improved estimation of the collisional timescale is compared with turbulence and expansion timescales to assess the relative importance of collisions. The collisional age computed using the . . .
Date: 04/2016 Publisher: The Astrophysical Journal Pages: 34 DOI: 10.3847/0004-637X/821/1/34 Available at:
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Authors: Kuznetsov V.D.
Title: Solar and heliospheric space missions

The paper provides a review of the state of the art and prospects of space research in heliophysics, in which a pivotal role belongs to magnetic measurements in the Sun and heliosphere. New space missions, such as the Interhelioprobe, Solar Orbiter, Solar Probe Plus, etc., will follow the currently operating ones (Hinode, SDO, STEREO, etc.) to observe the Sun from short distances and from out-of-ecliptic positions, as well as to conduct in situ measurements in the vicinity of the Sun and outside the ecliptic. The planned coordinated observations within the framework of these missions will allow us to explore the structure and dynamics of magnetic fields in the polar regions of the Sun, to study the mechanisms of the solar dynamo and solar cycle, to gain a deeper insight into the process. . .
Date: 02/2015 Publisher: Advances in Space Research Pages: 879 - 885 DOI: 10.1016/j.asr.2014.07.034 Available at:
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Authors: Kasper Justin C., Abiad Robert, Austin Gerry, Balat-Pichelin Marianne, Bale Stuart D., et al.
Title: Solar Wind Electrons Alphas and Protons (SWEAP) Investigation: Design of the Solar Wind and Coronal Plasma Instrument Suite for Solar Probe Plus

The Solar Wind Electrons Alphas and Protons (SWEAP) Investigation on Solar Probe Plus is a four sensor instrument suite that provides complete measurements of the electrons and ionized helium and hydrogen that constitute the bulk of solar wind and coronal plasma. SWEAP consists of the Solar Probe Cup (SPC) and the Solar Probe Analyzers (SPAN). SPC is a Faraday Cup that looks directly at the Sun and measures ion and electron fluxes and flow angles as a function of energy. SPAN consists of an ion and electron electrostatic analyzer (ESA) on the ram side of SPP (SPAN-A) and an electron ESA on the anti-ram side (SPAN-B). The SPAN-A ion ESA has a time of flight section that enables it to sort particles by their mass/charge ratio, permitting differentiation of ion species. SPAN-A and -B are r. . .
Date: 10/2015 Publisher: Space Science Reviews DOI: 10.1007/s11214-015-0206-3 Available at:
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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

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:
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Authors: Vainio Rami, önni Arttu, Battarbee Markus, Koskinen Hannu E. J., Afanasiev Alexandr, et al.
Title: A semi-analytical foreshock model for energetic storm particle events inside 1 AU

We have constructed a semi-analytical model of the energetic-ion foreshock of a CME-driven coronal/interplanetary shock wave responsible for the acceleration of large solar energetic particle (SEP) events. The model is based on the analytical model of diffusive shock acceleration of Bell (1978), appended with a temporal dependence of the cut-off momentum of the energetic particles accelerated at the shock, derived from the theory. Parameters of the model are re-calibrated using a fully time-dependent self-consistent simulation model of the coupled particle acceleration and Alfvén-wave generation upstream of the shock. Our results show that analytical estimates of the cut-off energy resulting from the simplified theory and frequently used in SEP modelling are overestimating the cut-off . . .
Date: 02/2014 Publisher: Journal of Space Weather and Space Climate Pages: A08 DOI: 10.1051/swsc/2014005 Available at:
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Authors: Peck Alison B., Benn Chris R., Seaman Robert L., Korreck Kelly E., Kasper Justin C., et al.
Title: SPIE ProceedingsSolar Wind Electrons Alphas and Protons (SWEAP) Science Operations Center initial design and implementation

Solar Probe Plus, scheduled to launch in 2018, is a NASA mission that will fly through the Sun's atmosphere for the first time. It will employ a combination of in situ plasma measurements and remote sensing imaging to achieve the mission's primary goal: to understand how the Sun's corona is heated and how the solar wind is accelerated. The Solar Wind Electrons Alphas and Protons (SWEAP) instrument suite consists of a Faraday cup and three electrostatic analyzers. In order to accomplish the science objectives, an encounter-based operations scheme is needed. This paper will outline the SWEAP science operations center design and schemes for data selection and down link. © (2014) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted f. . .
Date: Publisher: SPIE DOI: 10.1117/12.2057314 Available at:
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Authors: Korendyke Clarence M., Vourlidas Angelos, Plunkett Simon P., Howard Russell A., Wang Dennis, et al.
Title: SPIE ProceedingsDevelopment and test of an active pixel sensor detector for heliospheric imager on solar orbiter and solar probe plus
Abstract: N/A
Date: 10/2013 Publisher: SPIE DOI: 10.1117/12.2027655 Available at:
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Authors: Vourlidas Angelos, Howard Russell A., Plunkett Simon P., Korendyke Clarence M., Carter Michael T., et al.
Title: SPIE ProceedingsSeeing the corona with the solar probe plus mission: the wide-field imager for solar probe+ (WISPR)
Abstract: N/A
Date: 09/2013 Publisher: SPIE DOI: 10.1117/12.2027508 Available at:
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Authors: Lipatov Alexander S., Jr. Edward C. Sittler, Hartle Richard E., and Cooper John F.
Title: Short wavelength electromagnetic perturbations excited near the Solar Probe Plus spacecraft in the inner heliosphere: 2.5D hybrid modeling

A 2.5D numerical plasma model of the interaction of the solar wind (SW) with the Solar Probe Plus spacecraft (SPPSC) is presented. These results should be interpreted as a basic plasma model derived from the SW interaction with the spacecraft (SC), which could have consequences for both plasma wave and electron plasma measurements on board the SC in the inner heliosphere. Compression waves and electric field jumps with amplitudes of about 1.5 V/m and (12-18) V/m were also observed. A strong polarization electric field was also observed in the wing of the plasma wake. However, 2.5D hybrid modeling did not show excitation of whistler/Alfvén waves in the upstream connected with the bi-directional current closure that was observed in short-time 3D modeling SPPSC and near a tether in the io. . .
Date: 03/2012 Publisher: Planetary and Space Science Pages: 61 - 68 DOI: 10.1016/j.pss.2011.12.008 Available at:
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Authors: Rohner U, Saul L, Wurz P, Allegrini F, Scheer J, et al.
Title: A simple 3D plasma instrument with an electrically adjustable geometric factor for space research

We report on the design and experimental verification of a novel charged particle detector and an energy spectrometer with variable geometric factor functionality. Charged particle populations in the inner heliosphere create fluxes that can vary over many orders of magnitude in flux intensity. Space missions that plan to observe plasma fluxes, for example when travelling close to the Sun or to a planetary magnetosphere, require rapid particle measurements over the full three-dimensional velocity distribution. Traditionally, such measurements are carried out with plasma instrumentation with a fixed geometrical factor, which can only operate in a limited range of flux intensity. Here we report on the design and testing of a prototype sensor, which is capable of measuring particle flux wit. . .
Date: 02/2012 Publisher: Measurement Science and Technology Pages: 025901 DOI: 10.1088/0957-0233/23/2/025901 Available at:
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