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Authors: Panasenco Olga, Velli Marco, D’Amicis Raffaella, Shi Chen, Réville Victor, et al.
Title: Exploring Solar Wind Origins and Connecting Plasma Flows from the Parker Solar Probe to 1 au: Nonspherical Source Surface and Alfvénic Fluctuations

The magnetic field measurements of the FIELDS instrument on the Parker Solar Probe (PSP) have shown intensities, throughout its first solar encounter, that require a very low source surface (SS) height ( R SS ⩽1.8R ⊙  RSS⩽1.8R⊙ ) to be reconciled with magnetic field measurements at the Sun via potential field extrapolation (PFSS). However, during PSP’s second encounter, the situation went back to a more classic SS height ( R SS ⩽2.5R ⊙  RSS⩽2.5R⊙ ). Here we use high-resolution observations of the photospheric magnetic field (Solar Dynamics Observatory/Helioseismic and Magnetic Imager) to calculate neutral lines and boundaries of the open field regions for SS heights from 1.2 to 2.5 R<. . .
Date: 02/2020 Publisher: The Astrophysical Journal Supplement Series Pages: 54 DOI: 10.3847/1538-4365/ab61f4 Available at:
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Authors: Badman Samuel T., Bale Stuart D., Oliveros Juan C. Martín, Panasenco Olga, Velli Marco, et al.
Title: Magnetic Connectivity of the Ecliptic Plane within 0.5 au: Potential Field Source Surface Modeling of the First Parker Solar Probe Encounter

We compare magnetic field measurements taken by the FIELDS instrument on board Parker Solar Probe (PSP) during its first solar encounter to predictions obtained by potential field source surface (PFSS) modeling. Ballistic propagation is used to connect the spacecraft to the source surface. Despite the simplicity of the model, our results show striking agreement with PSP’s first observations of the heliospheric magnetic field from ̃0.5 au (107.5 R) down to 0.16 au (35.7 R). Further, we show the robustness of the agreement is improved both by allowing the photospheric input to the model to vary in time, and by advecting the field from PSP down to the PFSS model domain using in situ PSP/Solar Wind Electrons Alphas and Protons measurements of the solar wind sp. . .
Date: 02/2020 Publisher: The Astrophysical Journal Supplement Series Pages: 23 DOI: 10.3847/1538-4365/ab4da7 Available at:
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Authors: Tenerani Anna, Velli Marco, Matteini Lorenzo, Réville Victor, Shi Chen, et al.
Title: Magnetic Field Kinks and Folds in the Solar Wind

Parker Solar Probe (PSP) observations during its first encounter at 35.7 R have shown the presence of magnetic field lines that are strongly perturbed to the point that they produce local inversions of the radial magnetic field, known as switchbacks. Their counterparts in the solar wind velocity field are local enhancements in the radial speed, or jets, displaying (in all components) the velocity-magnetic field correlation typical of large amplitude Alfvén waves propagating away from the Sun. Switchbacks and radial jets have previously been observed over a wide range of heliocentric distances by Helios, Wind, and Ulysses, although they were prevalent in significantly faster streams than seen at PSP. Here we study via numerical magnetohydrodynamics simulations the evolutio. . .
Date: 02/2020 Publisher: The Astrophysical Journal Supplement Series Pages: 32 DOI: 10.3847/1538-4365/ab53e1 Available at:
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Authors: Réville Victor, Velli Marco, Panasenco Olga, Tenerani Anna, Shi Chen, et al.
Title: The Role of Alfvén Wave Dynamics on the Large-scale Properties of the Solar Wind: Comparing an MHD Simulation with Parker Solar Probe E1 Data

During Parker Solar Probe’s first orbit, the solar wind plasma was observed in situ closer than ever before, the perihelion on 2018 November 6 revealing a flow that is constantly permeated by large-amplitude Alfvénic fluctuations. These include radial magnetic field reversals, or switchbacks, that seem to be a persistent feature of the young solar wind. The measurements also reveal a very strong, unexpected, azimuthal velocity component. In this work, we numerically model the solar corona during this first encounter, solving the MHD equations and accounting for Alfvén wave transport and dissipation. We find that the large-scale plasma parameters are well reproduced, allowing the computation of the solar wind sources at Probe with confidence. We try to understand the dynamical nature. . .
Date: 02/2020 Publisher: The Astrophysical Journal Supplement Series Pages: 24 DOI: 10.3847/1538-4365/ab4fef Available at:
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Authors: Horbury Timothy S., Woolley Thomas, Laker Ronan, Matteini Lorenzo, Eastwood Jonathan, et al.
Title: Sharp Alfvénic Impulses in the Near-Sun Solar Wind

Measurements of the near-Sun solar wind by the Parker Solar Probe have revealed the presence of large numbers of discrete Alfvénic impulses with an anti-sunward sense of propagation. These are similar to those previously observed near 1 au, in high speed streams over the Sun’s poles and at 60 solar radii. At 35 solar radii, however, they are typically shorter and sharper than seen elsewhere. In addition, these spikes occur in "patches" and there are also clear periods within the same stream when they do not occur; the timescale of these patches might be related to the rate at which the spacecraft magnetic footpoint tracks across the coronal hole from which the plasma originated. While the velocity fluctuations associated with these spikes are typically under 100 km s-1, du. . .
Date: 02/2020 Publisher: The Astrophysical Journal Supplement Series Pages: 45 DOI: 10.3847/1538-4365/ab5b15 Available at:
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Authors: de Wit Thierry Dudok, Krasnoselskikh Vladimir V., Bale Stuart D., Bonnell John W., Bowen Trevor A., et al.
Title: Switchbacks in the Near-Sun Magnetic Field: Long Memory and Impact on the Turbulence Cascade

One of the most striking observations made by Parker Solar Probe during its first solar encounter is the omnipresence of rapid polarity reversals in a magnetic field that is otherwise mostly radial. These so-called switchbacks strongly affect the dynamics of the magnetic field. We concentrate here on their macroscopic properties. First, we find that these structures are self-similar, and have neither a characteristic magnitude, nor a characteristic duration. Their waiting time statistics show evidence of aggregation. The associated long memory resides in their occurrence rate, and is not inherent to the background fluctuations. Interestingly, the spectral properties of inertial range turbulence differ inside and outside of switchback structures; in the latter the 1/f range extends to hi. . .
Date: 02/2020 Publisher: The Astrophysical Journal Supplement Series Pages: 39 DOI: 10.3847/1538-4365/ab5853 Available at:
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Authors: Réville Victor, Velli Marco, Rouillard Alexis P., Lavraud Benoit, Tenerani Anna, et al.
Title: Tearing Instability and Periodic Density Perturbations in the Slow Solar Wind

In contrast with the fast solar wind, which originates in coronal holes, the source of the slow solar wind is still debated. Often intermittent and enriched with low first ionization potential elements—akin to what is observed in closed coronal loops—the slow wind could form in bursty events nearby helmet streamers. Slow winds also exhibit density perturbations that have been shown to be periodic and could be associated with flux ropes ejected from the tip of helmet streamers, as shown recently by the WISPR white-light imager on board Parker Solar Probe (PSP). In this work, we propose that the main mechanism controlling the release of flux ropes is a flow-modified tearing mode at the heliospheric current sheet (HCS). We use magnetohydrodynamic simulations of the solar wind and coron. . .
Date: 05/2020 Publisher: The Astrophysical Journal Pages: L20 DOI: 10.3847/2041-8213/ab911d Available at:
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Authors: Réville Victor, Tenerani Anna, and Velli Marco
Title: Parametric Decay and the Origin of the Low-frequency Alfvénic Spectrum of the Solar Wind

The fast solar wind shows a wide spectrum of transverse magnetic and velocity field perturbations. These perturbations are strongly correlated in the sense of Alfvén waves propagating mostly outward, from the Sun to the interplanetary medium. They are likely to be fundamental to the acceleration and the heating of the solar wind. However, the precise origin of the broadband spectrum is unknown to date. Typical periods of chromospheric Alfvén waves are limited to a few minutes, and any longer period perturbations should be strongly reflected at the transition region. In this work, we show that minute long Alfvénic fluctuations are unstable to the parametric instability. Parametric instability enables an inverse energy cascade by exciting several-hour-long periods of Alfvénic fluctuat. . .
Date: 10/2018 Publisher: The Astrophysical Journal Pages: 38 DOI: 10.3847/1538-4357/aadb8f Available at:
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Authors: Vourlidas Angelos, Howard Russell A., Plunkett Simon P., Korendyke Clarence M., Thernisien Arnaud F. R., et al.
Title: The Wide-Field Imager for Solar Probe Plus (WISPR)
Abstract: N/A
Date: 02/2015 Publisher: Space Science Reviews Pages: 83 - 130 DOI: 10.1007/s11214-014-0114-y 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: Velli Marco, Lionello Roberto, Linker Jon A., and ć Zoran

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:
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