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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: 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: Bastian T. S.
Title: AIP Conference ProceedingsA view from the ground: Next generation instrumentation for solar and heliospheric physics
Abstract:

The solar and space physics community has recently completed its second decadal survey under the auspices of the National Research Council. An integrated strategy for ground and space based studies of the Sun and space physics has been recommended, with specific recommendations made regarding new instrumentation, programs, and facilities. The ground based component of these recommendations is briefly reviewed here: the Advanced Technology Solar Telescope (ATST), the Frequency Agile Solar Radiotelescope (FASR), and the Coronal Solar Magnetism Observatory (COSMO). Although not considered as part of the decadal portfolio, but of which the community should nevertheless be aware, are the Atacama Large Millimeter/submillimeter Array (ALMA) and the Jansky Very Large Array (VLA). Several additi. . .
Date: 07/2013 Publisher: AIP DOI: 10.1063/1.4811080 Available at: http://aip.scitation.org/doi/abs/10.1063/1.4811080
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Authors: Wicks Robert T., Matteini Lorenzo, Horbury Timothy S., Hellinger Petr, and Roberts Aaron
Title: AIP Conference ProceedingsTemperature anisotropy instabilities; combining plasma and magnetic field data at different distances from the Sun
Abstract:

We present a new data analysis method enabling the observation of magnetic field fluctuations associated with temperature anisotropy instabilities using the Ulysses spacecraft. The movement of the spacecraft away from the Sun causes the observed plasma conditions, turbulent fluctuation amplitude, magnetic field strength and important physical scales to change. We normalize wavelet power spectra of the magnetic field using local values for the proton gyroscale and large scale magnetic field fluctuation amplitude to remove the effects of varying heliocentric distance. We recover the enhancement of magnetic fluctuations where temperature anisotropy instability growth rates are large, as seen by previous studies in the ecliptic at 1 AU. This method can be applied to any spacecraft data that. . .
Date: 07/2013 Publisher: AIP DOI: 10.1063/1.4811048 Available at: http://aip.scitation.org/doi/abs/10.1063/1.4811048
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Authors: Goelzer Molly L., Schwadron Nathan A., and Smith Charles W.
Title: An analysis of Alfvén radius based on sunspot number from 1749 to today
Abstract:

The Solar Probe Plus mission now under construction will provide the first in situ measurements from inside the orbit of Mercury. The most critical part of that mission will be measurements from inside the Alfvén radius where the Alfvén speed exceeds the wind speed and the physics of the solar wind changes fundamentally due, in part, to the multidirectionality of wave propagation. In this region waves from both sunward and antisunward of the observation point can effect the local dynamics including the turbulent evolution, heating, and acceleration of the plasma. While the location of this point can change with solar wind conditions, we ask the question of whether there is a systematic dependence on the solar cycle that moves the average Alfvén radius to different locations depending. . .
Date: 01/2014 Publisher: Journal of Geophysical Research: Space Physics Pages: 115 - 120 DOI: 10.1002/2013JA019420 Available at: http://doi.wiley.com/10.1002/2013JA019420http://onlinelibrary.wiley.com/wol1/doi/10.1002/2013JA019420/fullpdf
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Authors: Nieves-Chinchilla Teresa, Szabo Adam, Korreck Kelly E., Alzate Nathalia, Balmaceda Laura A., et al.
Title: Analysis of the Internal Structure of the Streamer Blowout Observed by the Parker Solar Probe During the First Solar Encounter
Abstract:

In this paper, we present an analysis of the internal structure of a coronal mass ejection (CME) detected by in situ instruments on board the Parker Solar Probe (PSP) spacecraft during its first solar encounter. On 2018 November 11 at 23:53 UT, the FIELDS magnetometer measured an increase in strength of the magnetic field as well as a coherent change in the field direction. The SWEAP instrument simultaneously detected a low proton temperature and signatures of bidirectionality in the electron pitch angle distribution (PAD). These signatures are indicative of a CME embedded in the slow solar wind. Operating in conjunction with PSP was the STEREO A spacecraft, which enabled the remote observation of a streamer blowout by the SECCHI suite of instruments. The source at the Sun of the slow a. . .
Date: 02/2020 Publisher: The Astrophysical Journal Supplement Series Pages: 63 DOI: 10.3847/1538-4365/ab61f5 Available at: https://iopscience.iop.org/article/10.3847/1538-4365/ab61f5
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Authors: Maksimovic M., Bale S. D., Berčič L., Bonnell J. W., Case A. W., et al.
Title: Anticorrelation between the Bulk Speed and the Electron Temperature in the Pristine Solar Wind: First Results from the Parker Solar Probe and Comparison with Helios
Abstract:

We discuss the solar wind electron temperatures Te as measured in the nascent solar wind by Parker Solar Probe during its first perihelion pass. The measurements have been obtained by fitting the high-frequency part of quasi-thermal noise spectra recorded by the Radio Frequency Spectrometer. In addition we compare these measurements with those obtained by the electrostatic analyzer discussed in Halekas et al. These first electron observations show an anticorrelation between Te and the wind bulk speed V: this anticorrelation is most likely the remnant of the well-known mapping observed at 1 au and beyond between the fast wind and its coronal hole sources, where electrons are observed to be cooler than in the quiet corona. We also revisit Helios electron temperature . . .
Date: 02/2020 Publisher: The Astrophysical Journal Supplement Series Pages: 62 DOI: 10.3847/1538-4365/ab61fc Available at: https://iopscience.iop.org/article/10.3847/1538-4365/ab61fch
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Authors: Chhiber Rohit, Goldstein M L., Maruca B. A., Chasapis A., Matthaeus W. H., et al.
Title: Clustering of Intermittent Magnetic and Flow Structures near Parker Solar Probe ’s First Perihelion—A Partial-variance-of-increments Analysis
Abstract:

During the Parker Solar Probe’s (PSP) first perihelion pass, the spacecraft reached within a heliocentric distance of ̃37 R and observed numerous magnetic and flow structures characterized by sharp gradients. To better understand these intermittent structures in the young solar wind, an important property to examine is their degree of correlation in time and space. To this end, we use the well-tested partial variance of increments (PVI) technique to identify intermittent events in FIELDS and SWEAP observations of magnetic and proton-velocity fields (respectively) during PSP’s first solar encounter, when the spacecraft was within 0.25 au from the Sun. We then examine distributions of waiting times (WT) between events with varying separation and PVI thresholds. We find . . .
Date: 02/2020 Publisher: The Astrophysical Journal Supplement Series Pages: 31 DOI: 10.3847/1538-4365/ab53d2 Available at: https://iopscience.iop.org/article/10.3847/1538-4365/ab53d2
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Authors: Bowen Trevor A., Mallet Alfred, Bale Stuart D., Bonnell J. W., Case Anthony W., et al.
Title: Constraining Ion-Scale Heating and Spectral Energy Transfer in Observations of Plasma Turbulence
Abstract:

We perform a statistical study of the turbulent power spectrum at inertial and kinetic scales observed during the first perihelion encounter of the Parker Solar Probe. We find that often there is an extremely steep scaling range of the power spectrum just above the ion-kinetic scales, similar to prior observations at 1 A.U., with a power-law index of around -4 . Based on our measurements, we demonstrate that either a significant (>50 %) fraction of the total turbulent energy flux is dissipated in this range of scales, or the characteristic nonlinear interaction time of the turbulence decreases dramatically from the expectation based solely on the dispersive nature of nonlinearly interacting kinetic Alfvén waves.


Date: 07/2020 Publisher: Physical Review Letters DOI: 10.1103/PhysRevLett.125.025102 Available at: https://link.aps.org/doi/10.1103/PhysRevLett.125.025102
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Authors: Tracy Patrick J., Kasper Justin C., Raines Jim M., Shearer Paul, Gilbert Jason A., et al.
Title: Constraining Solar Wind Heating Processes by Kinetic Properties of Heavy Ions
Abstract:

We analyze the heavy ion components (A >4 amu ) in collisionally young solar wind plasma and show that there is a clear, stable dependence of temperature on mass, probably reflecting the conditions in the solar corona. We consider both linear and power law forms for the dependence and find that a simple linear fit of the form Ti/Tp=(1.35 ±.02 )mi/mp describes the observations twice as well as the equivalent best fit power law of the form Ti/Tp=(mi/mp) 1.07 ±.01 . Most importantly we find that current model predictions based on turbulent transport and kinetic dissipation are in agreement with observed nonthermal heating in intermediate collisional age plasma for m /q <3.5 , but are . . .
Date: 06/2016 Publisher: Physical Review Letters DOI: 10.1103/PhysRevLett.116.255101 Available at: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.255101
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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: Berčič Laura, Larson Davin, Whittlesey Phyllis, Maksimovic Milan, Badman Samuel T., et al.
Title: Coronal Electron Temperature Inferred from the Strahl Electrons in the Inner Heliosphere: Parker Solar Probe and Helios Observations
Abstract:

The shape of the electron velocity distribution function plays an important role in the dynamics of the solar wind acceleration. Electrons are normally modeled with three components, the core, the halo, and the strahl. We investigate how well the fast strahl electrons in the inner heliosphere preserve the information about the coronal electron temperature at their origin. We analyzed the data obtained by two missions, Helios, spanning the distances between 65 and 215 RS, and Parker Solar Probe (PSP), reaching down to 35 RS during its first two orbits around the Sun. The electron strahl was characterized with two parameters: pitch-angle width (PAW) and the strahl parallel temperature (Ts||). PSP observations confirm the already reported dependence of stra. . .
Date: 04/2020 Publisher: The Astrophysical Journal Pages: 88 DOI: 10.3847/1538-4357/ab7b7a Available at: https://iopscience.iop.org/article/10.3847/1538-4357/ab7b7a
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Authors: Velli Marco, Lionello Roberto, Linker Jon A., and ć Zoran
Title: CORONAL PLUMES IN THE FAST SOLAR WIND
Abstract:

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

The Parker Solar Probe (PSP) has observed copious rapid magnetic field direction changes in the near-Sun solar wind. These features have been called "switchbacks," and their origin is a mystery. But their widespread nature suggests that they may be generated by a frequently occurring process in the Sun’s atmosphere. We examine the possibility that the switchbacks originate from coronal jets. Recent work suggests that many coronal jets result when photospheric magnetic flux cancels, and forms a small-scale "minifilament" flux rope that erupts and reconnects with coronal field. We argue that the reconnected erupting-minifilament flux rope can manifest as an outward propagating Alfvénic fluctuation that steepens into an increasingly compact disturbance as it moves through the solar wind. . .
Date: 06/2020 Publisher: The Astrophysical Journal Pages: L18 DOI: 10.3847/2041-8213/ab96be Available at: https://iopscience.iop.org/article/10.3847/2041-8213/ab96behttps://iopscience.iop.org/article/10.3847/2041-8213/ab96be/
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Authors: McManus Michael D., Bowen Trevor A., Mallet Alfred, Chen Christopher H. K., Chandran Benjamin D. G., et al.
Title: Cross Helicity Reversals in Magnetic Switchbacks
Abstract:

We consider 2D joint distributions of normalized residual energy, σr(s, t), and cross helicity, σc(s, t), during one day of Parker Solar Probe’s (PSP’s) first encounter as a function of wavelet scale s. The broad features of the distributions are similar to previous observations made by Helios in slow solar wind, namely well-correlated and fairly Alfvénic wind, except for a population with negative cross helicity that is seen at shorter wavelet scales. We show that this population is due to the presence of magnetic switchbacks, or brief periods where the magnetic field polarity reverses. Such switchbacks have been observed before, both in Helios data and in Ulysses data in the polar solar wind. Their abundance and short timescales as seen by PSP in its first. . .
Date: 02/2020 Publisher: The Astrophysical Journal Supplement Series Pages: 67 DOI: 10.3847/1538-4365/ab6dce Available at: https://iopscience.iop.org/article/10.3847/1538-4365
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Authors: Marchand R., Miyake Y., Usui H., Deca J., Lapenta G., et al.
Title: Cross-comparison of spacecraft-environment interaction model predictions applied to Solar Probe Plus near perihelion
Abstract:

Five spacecraft-plasma models are used to simulate the interaction of a simplified geometry Solar Probe Plus (SPP) satellite with the space environment under representative solar wind conditions near perihelion. By considering similarities and differences between results obtained with different numerical approaches under well defined conditions, the consistency and validity of our models can be assessed. The impact on model predictions of physical effects of importance in the SPP mission is also considered by comparing results obtained with and without these effects. Simulation results are presented and compared with increasing levels of complexity in the physics of interaction between solar environment and the SPP spacecraft. The comparisons focus particularly on spacecraft floating po. . .
Date: 06/2014 Publisher: Physics of Plasmas Pages: 062901 DOI: 10.1063/1.4882439 Available at: http://aip.scitation.org/doi/10.1063/1.4882439http://aip.scitation.org/doi/pdf/10.1063/1.4882439
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Authors: Witze Alexandra
Title: Death-defying NASA mission will make humanity’s closest approach to the Sun
Abstract:

The Parker Solar Probe will dive into the sizzling solar corona to explore its mysteries.


Date: 07/2018 Publisher: Nature Pages: 452 - 453 DOI: 10.1038/d41586-018-05741-6 Available at: http://www.nature.com/articles/d41586-018-05741-6http://www.nature.com/articles/d41586-018-05741-6.pdfhttp://www.nature.com/articles/d41586-018-05741-6http://www.nature.com/articles/d41586-018-05741-6.pdf
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Authors: Krupar Vratislav, Szabo Adam, Maksimovic Milan, Kruparova Oksana, Kontar Eduard P., et al.
Title: Density Fluctuations in the Solar Wind Based on Type III Radio Bursts Observed by Parker Solar Probe
Abstract:

Radio waves are strongly scattered in the solar wind, so that their apparent sources seem to be considerably larger and shifted than the actual ones. Since the scattering depends on the spectrum of density turbulence, a better understanding of the radio wave propagation provides indirect information on the relative density fluctuations, ϵ=⟨δn⟩/⟨n⟩ ϵ=⟨δn⟩/⟨n⟩ , at the effective turbulence scale length. Here, we analyzed 30 type III bursts detected by Parker Solar Probe (PSP). For the first time, we retrieved type III burst decay times, τ d  τd , between 1 and 10 MHz thanks to an unparalleled temporal resolution of PSP. We observed a significant deviation in a power-law slope for frequencies above 1 MHz. . .
Date: 02/2020 Publisher: The Astrophysical Journal Supplement Series Pages: 57 DOI: 10.3847/1538-4365/ab65bd Available at: https://iopscience.iop.org/article/10.3847/1538-4365/ab65bd
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Authors: Hanneson Cedar, Johnson Catherine L., Mittelholz Anna, Asad Manar M. Al, and Goldblatt Colin
Title: Dependence of the Interplanetary Magnetic Field on Heliocentric Distance at 0.3–1.7 AU: A Six‐Spacecraft Study
Abstract:

We use magnetometer data taken simultaneously by MESSENGER, VEX, STEREO and ACE to characterize the variation of the interplanetary magnetic field (IMF) with heliocentric distance, rh, for rh≲ 1 AU. Power law fits (a rh b) to the individual IMF components and magnitude indicate that, on average, the IMF is more tightly wound and its strength decreases less rapidly with rh than the Parker spiral prediction. During Solar Cycle 24, temporal changes in b were insignificant, but changes in amplitude, a, were correlated with sunspot number, up to sunspot number ∼84. MAVEN data taken at 1.4-1.7 AU since late 2014 broadly confirm and extend these results in space and time. Our study demonstrates the importance of simultaneous observations from multiple spacecraft to separate heliocentric di. . .
Date: 03/2020 Publisher: Journal of Geophysical Research: Space Physics DOI: 10.1029/2019JA027139 Available at: https://onlinelibrary.wiley.com/doi/abs/10.1029/2019JA027139
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Authors: Poirier Nicolas, Kouloumvakos Athanasios, Rouillard Alexis P., Pinto Rui F., Vourlidas Angelos, et al.
Title: Detailed Imaging of Coronal Rays with the Parker Solar Probe
Abstract:

The Wide-field Imager for Solar PRobe (WISPR) obtained the first high-resolution images of coronal rays at heights below 15 R when the Parker Solar Probe (PSP) was located inside 0.25 au during the first encounter. We exploit these remarkable images to reveal the structure of coronal rays at scales that are not easily discernible in images taken from near 1 au. To analyze and interpret WISPR observations, which evolve rapidly both radially and longitudinally, we construct a latitude versus time map using the full WISPR data set from the first encounter. From the exploitation of this map and also from sequential WISPR images. we show the presence of multiple substructures inside streamers and pseudostreamers. WISPR unveils the fine-scale structure of the densest part of str. . .
Date: 02/2020 Publisher: The Astrophysical Journal Supplement Series Pages: 60 DOI: 10.3847/1538-4365/ab6324 Available at: https://iopscience.iop.org/article/10.3847/1538-4365/ab6324
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Authors: Howes Gregory G., Klein Kristopher G., and Li Tak Chu
Title: Diagnosing collisionless energy transfer using field–particle correlations: Vlasov–Poisson plasmas
Abstract:

Turbulence plays a key role in the conversion of the energy of large-scale fields and flows to plasma heat, impacting the macroscopic evolution of the heliosphere and other astrophysical plasma systems. Although we have long been able to make direct spacecraft measurements of all aspects of the electromagnetic field and plasma fluctuations in near-Earth space, our understanding of the physical mechanisms responsible for the damping of the turbulent fluctuations in heliospheric plasmas remains incomplete. Here we propose an innovative field-particle correlation technique that can be used to measure directly the secular energy transfer from fields to particles associated with collisionless damping of the turbulent fluctuations. Furthermore, this novel procedure yields information about th. . .
Date: 02/2017 Publisher: Journal of Plasma Physics DOI: 10.1017/S0022377816001197 Available at: https://www.cambridge.org/core/product/identifier/S0022377816001197/type/journal_article
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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: Malaspina David M., Ergun Robert E., Bolton Mary, Kien Mark, Summers David, et al.
Title: The Digital Fields Board for the FIELDS instrument suite on the Solar Probe Plus mission: Analog and digital signal processing
Abstract:

The first in situ measurements of electric and magnetic fields in the near-Sun environment (< 0.25 AU from the Sun) will be made by the FIELDS instrument suite on the Solar Probe Plus mission. The Digital Fields Board (DFB) is an electronics board within FIELDS that performs analog and digital signal processing, as well as digitization, for signals between DC and 60 kHz from five voltage sensors and four search coil magnetometer channels. These nine input signals are processed on the DFB into 26 analog data streams. A specialized application-specific integrated circuit performs analog to digital conversion on all 26 analog channels simultaneously. The DFB then processes the digital data using a field programmable gate array (FPGA), generating a variety of data products, including dig. . .
Date: 06/2016 Publisher: Journal of Geophysical Research: Space Physics Pages: 5088 - 5096 DOI: 10.1002/2016JA022344 Available at: http://doi.wiley.com/10.1002/2016JA022344http://onlinelibrary.wiley.com/wol1/doi/10.1002/2016JA022344/fullpdf
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Authors: Adhikari L., Zank G. P., and Zhao L.-L.
Title: Does Turbulence Turn off at the Alfvén Critical Surface?
Abstract:

The Parker Solar Probe (PSP) will eventually reach and cross the Alfvén point or surface as it provides us with direct in situ measurements of the solar atmosphere. The Alfvén surface is the location at which the large-scale bulk solar wind speed ${\boldsymbol{U}}$ and the Alfvén speed ${\boldsymbol{V}}$ A are equal, and thus it separates sub-Aflvénic coronal flow $| {\boldsymbol{U}}| \ll | {{\boldsymbol{V}}}_{{\rm{A}}}| $ from super-Alfv. . .
Date: Jan-05-2019 Publisher: The Astrophysical Journal Pages: 26 DOI: 10.3847/1538-4357/ab141c Available at: https://iopscience.iop.org/article/10.3847/1538-4357/ab141c
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Authors: Adhikari L., Zank G. P., and Zhao L.-L.
Title: Does Turbulence Turn off at the Alfvén Critical Surface?
Abstract:

The Parker Solar Probe (PSP) will eventually reach and cross the Alfvén point or surface as it provides us with direct in situ measurements of the solar atmosphere. The Alfvén surface is the location at which the large-scale bulk solar wind speed $\boldsymbolU$ and the Alfvén speed $\boldsymbolV$ A are equal, and thus it separates sub-Aflvénic coronal flow $| \boldsymbolU| \ll | {\boldsymbolV_{\rmA| $ from super-Alfvénic solar wind flow&n. . .
Date: Jan-05-2019 Publisher: The Astrophysical Journal Pages: 26 DOI: 10.3847/1538-4357/ab141c Available at: https://iopscience.iop.org/article/10.3847/1538-4357/ab141c
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