Found 193 results
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2020
Authors: Schwadron N. A., Bale S., Bonnell J., Case A., Christian E. R., et al.
Title: Seed Population Preconditioning and Acceleration Observed by the Parker Solar Probe
Abstract:

A series of solar energetic particle (SEP) events was observed by the Integrated Science Investigation of the Sun (IS☉IS) on the Parker Solar Probe (PSP) during the period from 2019 April 18 through 24. The PSP spacecraft was located near 0.48 au from the Sun on Parker spiral field lines that projected out to 1 au within ̃25° of the near-Earth spacecraft. These SEP events, though small compared to historically large SEP events, were among the largest observed thus far in the PSP mission and provide critical information about the space environment inside 1 au during SEP events. During this period, the Sun released multiple coronal mass ejections (CMEs). One of these CMEs observed was initiated on 2019 April 20 at 01:25 UTC, and the interplanetary CME (ICME) propagated out and passed . . .
Date: 02/2020 Publisher: The Astrophysical Journal Supplement Series Pages: 33 DOI: 10.3847/1538-4365/ab5527 Available at: https://iopscience.iop.org/article/10.3847/1538-4365/ab5527
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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
Abstract:

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: https://iopscience.iop.org/article/10.3847/1538-4365/ab5b15
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Authors: Nisticò Giuseppe, Bothmer Volker, Vourlidas Angelos, Liewer Paulett C., Thernisien Arnaud F., et al.
Title: Simulating White-Light Images of Coronal Structures for Parker Solar Probe/WISPR: Study of the Total Brightness Profiles
Abstract:

The Wide-field Imager for Parker Solar Probe (WISPR) captures unprecedented white-light images of the solar corona and inner heliosphere. Thanks to the uniqueness of the Parker Solar Probe's (PSP) orbit, WISPR is able to image "locally" coronal structures at high spatial and time resolutions. The observed plane of sky, however, rapidly changes because of the PSP's high orbital speed. Therefore, the interpretation of the dynamics of the coronal structures recorded by WISPR is not straightforward. A first study, undertaken by Liewer et al. (Solar Phys.294, 93, 2019), shows how different coronal features (e.g., streamers, flux ropes) appear in the field-of-view of WISPR by means of raytracing simulations. In particular, they analyze the effects of the spatial resolution changes on both the. . .
Date: 04/2020 Publisher: Solar Physics DOI: 10.1007/s11207-020-01626-y Available at: http://link.springer.com/10.1007/s11207-020-01626-yhttp
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Authors: Hill M. E., Mitchell D. G., Allen R. C., de Nolfo G. A., Vourlidas A., et al.
Title: Small, Low-energy, Dispersive Solar Energetic Particle Events Observed by Parker Solar Probe
Abstract:

The Energetic Particle Instrument─Low Energy (EPI-Lo) experiment has detected several weak, low-energy (̃30─300 keV nucleon─1) solar energetic particle (SEP) events during its first two closest approaches to the Sun, providing a unique opportunity to explore the sources of low-energy particle acceleration. As part of the Parker Solar Probe (PSP) Integrated Science Investigation of the Sun (IS☉IS) suite, EPI-Lo was designed to investigate the physics of energetic particles; however, in the special lowest-energy "time-of-flight only" product used in this study, it also responds to solar photons in a subset of approximately sunward-looking apertures lacking special light-attenuating foils. During the first three perihelia, in a frame rotating with the Sun, PSP undergoes. . .
Date: 02/2020 Publisher: The Astrophysical Journal Supplement Series Pages: 65 DOI: 10.3847/1538-4365/ab643d Available at: https://iopscience.iop.org/article/10.3847/1538-4365/ab643
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Authors: Giacalone J., Mitchell D. G., Allen R. C., Hill M. E., McNutt R. L., et al.
Title: Solar Energetic Particles Produced by a Slow Coronal Mass Ejection at ∼0.25 au
Abstract:

We present an analysis of Parker Solar Probe (PSP) IS☉IS observations of ̃30─300 keV n−1 ions on 2018 November 11 when PSP was about 0.25 au from the Sun. Five hours before the onset of a solar energetic particle (SEP) event, a coronal mass ejection (CME) was observed by STEREO-A/COR2, which crossed PSP about a day later. No shock was observed locally at PSP, but the CME may have driven a weak shock earlier. The SEP event was dispersive, with higher energy ions arriving before the lower energy ones. Timing suggests the particles originated at the CME when it was at ̃7.4R. SEP intensities increased gradually from their onset over a few hours, reaching a peak, and then decreased gradually before the CME arrived at PSP. The event was weak, having a very sof. . .
Date: 02/2020 Publisher: The Astrophysical Journal Supplement Series Pages: 29 DOI: 10.3847/1538-4365/ab5221 Available at: https://iopscience.iop.org/article/10.3847/1538-4365/ab5221
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Authors: Case A. W., Kasper Justin C., Stevens Michael L., Korreck Kelly E., Paulson Kristoff, et al.
Title: The Solar Probe Cup on the Parker Solar Probe
Abstract:

Solar Probe Cup (SPC) is a Faraday cup instrument on board NASA's Parker Solar Probe (PSP) spacecraft designed to make rapid measurements of thermal coronal and solar wind plasma. The spacecraft is in a heliocentric orbit that takes it closer to the Sun than any previous spacecraft, allowing measurements to be made where the coronal and solar wind plasma is being heated and accelerated. The SPC instrument was designed to be pointed directly at the Sun at all times, allowing the solar wind (which is flowing primarily radially away from the Sun) to be measured throughout the orbit. The instrument is capable of measuring solar wind ions with an energy between 100 and 6000 V (protons with speeds from 139 to 1072 km s−1). It also measures electrons with an energy/charge between . . .
Date: 02/2020 Publisher: The Astrophysical Journal Supplement Series Pages: 43 DOI: 10.3847/1538-4365/ab5a7b Available at: https://iopscience.iop.org/article/10.3847/1538-4365/ab5a7b
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Authors: Allen R. C., Lario D., Odstrcil D., Ho G. C., Jian L. K., et al.
Title: Solar Wind Streams and Stream Interaction Regions Observed by the Parker Solar Probe with Corresponding Observations at 1 au
Abstract:

Several fast solar wind streams and stream interaction regions (SIRs) were observed by the Parker Solar Probe (PSP) during its first orbit (2018 September─2019 January). During this time, several recurring SIRs were also seen at 1 au at both L1 (Advanced Composition Explorer (ACE) and Wind) and the location of the Solar Terrestrial Relations Observatory-Ahead (STEREO-A). In this paper, we compare four fast streams observed by PSP at different radial distances during its first orbit. For three of these fast stream events, measurements from L1 (ACE and Wind) and STEREO-A indicated that the fast streams were observed by both PSP and at least one of the 1 au monitors. Our associations are supported by simulations made by the ENLIL model driven by GONG-(ADAPT-)WSA, which allows us to conte. . .
Date: 02/2020 Publisher: The Astrophysical Journal Supplement Series Pages: 36 DOI: 10.3847/1538-4365/ab578f Available at: https://iopscience.iop.org/article/10.3847/1538-4365/ab578f
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Authors: Korreck Kelly E., Szabo Adam, Chinchilla Teresa Nieves, Lavraud Benoit, Luhmann Janet, et al.
Title: Source and Propagation of a Streamer Blowout Coronal Mass Ejection Observed by the Parker Solar Probe
Abstract:

In the first orbit of the Parker Solar Probe (PSP), in situ thermal plasma and magnetic field measurements were collected as close as 35 RSun from the Sun, an environment that had not been previously explored. During the first orbit of PSP, the spacecraft flew through a streamer blowout coronal mass ejection (SBO-CME) on 2018 November 11 at 23:50 UT as it exited the science encounter. The SBO-CME on November 11 was directed away from the Earth and was not visible by L1 or Earth-based telescopes due to this geometric configuration. However, PSP and the STEREO-A spacecraft were able to make observations of this slow (v ≈ 380 km s−1) SBO-CME. Using the PSP data, STEREO-A images, and Wang─Sheeley─Arge model, the source region of the CME is found to be a helmet . . .
Date: 02/2020 Publisher: The Astrophysical Journal Supplement Series Pages: 69 DOI: 10.3847/1538-4365/ab6ff9 Available at: https://iopscience.iop.org/article/10.3847/1538-4365/ab6ff9
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Authors: Pulupa Marc, Bale Stuart D., Badman Samuel T., Bonnell J. W., Case Anthony W., et al.
Title: Statistics and Polarization of Type III Radio Bursts Observed in the Inner Heliosphere
Abstract:

We present initial results from the Radio Frequency Spectrometer, the high-frequency component of the FIELDS experiment on the Parker Solar Probe (PSP). During the first PSP solar encounter (2018 November), only a few small radio bursts were observed. During the second encounter (2019 April), copious type III radio bursts occurred, including intervals of radio storms where bursts occurred continuously. In this paper, we present initial observations of the characteristics of type III radio bursts in the inner heliosphere, calculating occurrence rates, amplitude distributions, and spectral properties of the observed bursts. We also report observations of several bursts during the second encounter that display circular polarization in the right-hand-polarized sense, with a degree of polari. . .
Date: 02/2020 Publisher: The Astrophysical Journal Supplement Series Pages: 49 DOI: 10.3847/1538-4365/ab5dc0 Available at: https://iopscience.iop.org/article/10.3847/1538-4365/ab5dc0
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Authors: Agapitov O. V., de Wit Dudok, Mozer F. S., Bonnell J. W., Drake J. F., et al.
Title: Sunward-propagating Whistler Waves Collocated with Localized Magnetic Field Holes in the Solar Wind: Parker Solar Probe Observations at 35.7 R Radii
Abstract:

Observations by the Parker Solar Probe mission of the solar wind at ∼35.7 solar radii reveal the existence of whistler wave packets with frequencies below 0.1 fce (20-80 Hz in the spacecraft frame). These waves often coincide with local minima of the magnetic field magnitude or with sudden deflections of the magnetic field that are called switchbacks. Their sunward propagation leads to a significant Doppler frequency downshift from 200-300 to 20-80 Hz (from 0.2 to 0.5 fce). The polarization of these waves varies from quasi-parallel to significantly oblique with wave normal angles that are close to the resonance cone. Their peak amplitude can be as large as 2-4 nT. Such values represent approximately 10% of the background magnetic field, which is considerably more. . .
Date: 03/2020 Publisher: The Astrophysical Journal Pages: L20 DOI: 10.3847/2041-8213/ab799c Available at: https://iopscience.iop.org/article/10.3847/2041-8213/ab799c
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Authors: Wiedenbeck M. E., Bučík R., Mason G. M., Ho G. C., Leske R. A., et al.
Title: 3 He-rich Solar Energetic Particle Observations at the Parker Solar Probe and near Earth
Abstract:

The Integrated Science Investigation of the Sun (IS☉IS) instrument suite on the Parker Solar Probe (PSP) spacecraft is making in situ observations of energetic ions and electrons closer to the Sun than any previous mission. Using data collected during its first two orbits, which reached perihelion distances of 0.17 au, we have searched for  3 He 3He -rich solar energetic particle (SEP) events under very quiet solar minimum conditions. On 2019-110─111 (April 20─21),  3 He 3He -rich SEPs were observed at energies near 1 MeV nucleon─1 in association with energetic protons, heavy ions, and electrons. This activity was also detected by the Ultra-Low-Energy Isotope Spectrometer and the Electron, Proton, and Alpha Monitor instruments on the Adva. . .
Date: 02/2020 Publisher: The Astrophysical Journal Supplement Series Pages: 42 DOI: 10.3847/1538-4365/ab5963 Available at: https://iopscience.iop.org/article/10.3847/1538-4365/ab5963
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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
Abstract:

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: https://iopscience.iop.org/article/10.3847/1538-4365/ab5853
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Authors: Mozer F. S., Agapitov O. V., Bale S. D., Bonnell J. W., Case T., et al.
Title: Switchbacks in the Solar Magnetic Field: Their Evolution, Their Content, and Their Effects on the Plasma
Abstract:

Switchbacks (rotations of the magnetic field) are observed on the Parker Solar Probe. Their evolution, content, and plasma effects are studied in this paper. The solar wind does not receive a net acceleration from switchbacks that it encountered upstream of the observation point. The typical switchback rotation angle increased with radial distance. Significant Poynting fluxes existed inside, but not outside, switchbacks, and the dependence of the Poynting flux amplitude on the switchback radial location and rotation angle is explained quantitatively as being proportional to (B sin(θ))2. The solar wind flow inside switchbacks was faster than that outside due to the frozen-in ions moving with the magnetic structure at the Alfvén speed. This energy gain results from the diverg. . .
Date: 02/2020 Publisher: The Astrophysical Journal Supplement Series Pages: 68 DOI: 10.3847/1538-4365/ab7196 Available at: https://iopscience.iop.org/article/10.3847/1538-4365/ab7196
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Authors: Mozer F. S., Agapitov O. V., Bale S. D., Bonnell J. W., Goetz K., et al.
Title: Time Domain Structures and Dust in the Solar Vicinity: Parker Solar Probe Observations
Abstract:

On 2019 April 5, while the Parker Solar Probe was at its 35 solar radius perihelion, the data set collected at 293 samples/s contained more than 10,000 examples of spiky electric-field-like structures with durations less than 200 milliseconds and amplitudes greater than 10 mV m−1. The vast majority of these events were caused by plasma turbulence. Defining dust events as those with similar, narrowly peaked, positive, and single-ended signatures resulted in finding 135 clear dust events, which, after correcting for the low detection efficiently, resulted in an estimate consistent with the 1000 dust events expected from other techniques. Defining time domain structures (TDS) as those with opposite polarity signals in the opposite antennas resulted in finding 238 clear TDS eve. . .
Date: 02/2020 Publisher: The Astrophysical Journal Supplement Series Pages: 50 DOI: 10.3847/1538-4365/ab5e4b Available at: https://iopscience.iop.org/article/10.3847/1538-4365/ab5e4b
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Authors: Adhikari L., Zank G. P., Zhao L.-L., Kasper J. C., Korreck K. E., et al.
Title: Turbulence Transport Modeling and First Orbit Parker Solar Probe ( PSP ) Observations
Abstract:

The Parker Solar Probe (PSP) achieved its first orbit perihelion on 2018 November 6, reaching a heliocentric distance of about 0.165 au (35.55 R). Here, we study the evolution of fully developed turbulence associated with the slow solar wind along the PSP trajectory between 35.55 R and 131.64 R in the outbound direction, comparing observations to a theoretical turbulence transport model. Several turbulent quantities, such as the fluctuating kinetic energy and the corresponding correlation length, the variance of density fluctuations, and the solar wind proton temperature are determined from the PSP Solar Wind Electrons Alphas and Protons (SWEAP) plasma data along its trajectory between 35.55 R and 131.64 R. The evolut. . .
Date: 02/2020 Publisher: The Astrophysical Journal Supplement Series Pages: 38 DOI: 10.3847/1538-4365/ab5852 Available at: https://iopscience.iop.org/article/10.3847/1538-4365/ab5852
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Authors: Longcope Dana
Title: Using Kepler's laws and Rutherford scattering to chart the seven gravity assists in the epic sunward journey of the Parker Solar Probe
Abstract:

On August 12, 2018, NASA launched the Parker Solar Probe (PSP) to explore regions very near the Sun. Losing enough energy and angular momentum to approach the Sun requires either an impractical amount of fuel or a maneuver called a gravity assist. A gravity assist is essentially an elastic collision with a massive, moving target—Rutherford scattering from a planet. Gravity assists are often used to gain energy in missions destined for the outer solar system, but they can also be used to lose energy. Reaching an orbit sufficiently close to the Sun requires that PSP undergoes not one but seven successive gravity assists off the planet Venus. This simple description poses several conceptual challenges to the curious physics student. Why is it so much more challenging to get to the Sun th. . .
Date: 01/2020 Publisher: American Journal of Physics Pages: 11 - 19 DOI: 10.1119/10.0000145 Available at: http://aapt.scitation.org/doi/10.1119/10.0000145http://aapt.scitation.org/doi/pdf/10.1119/10.0000145
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Authors: Morgan Huw, and Cook Anthony C.
Title: The Width, Density, and Outflow of Solar Coronal Streamers
Abstract:

Characterizing the large-scale structure and plasma properties of the inner corona is crucial to understanding the source and subsequent expansion of the solar wind and related space weather effects. Here, we apply a new coronal rotational tomography method, along with a method to narrow streamers and refine the density estimate, to COR2A/Solar Terrestrial Relations Observatory observations from a period near solar minimum and maximum, gaining density maps for heights between 4 and 8R. The coronal structure is highly radial at these heights, and the streamers are very narrow: in some regions, only a few degrees in width. The mean densities of streamers is almost identical between solar minimum and maximum. However, streamers at solar maximum contain around 50% more total m. . .
Date: 04/2020 Publisher: The Astrophysical Journal Pages: 57 DOI: 10.3847/1538-4357/ab7e32 Available at: https://iopscience.iop.org/article/10.3847/1538-4357/ab7e32
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Authors: Hess Phillip, Rouillard Alexis P., Kouloumvakos Athanasios, Liewer Paulett C., Zhang Jie, et al.
Title: WISPR Imaging of a Pristine CME
Abstract:

The Wide-field Imager for Solar Probe (WISPR) on board the Parker Solar Probe (PSP) observed a coronal mass ejection (CME) on 2018 November 1, the first day of the initial PSP encounter. The speed of the CME, approximately 200─300 km s−1 in the WISPR field of view, is typical of slow, streamer blowout CMEs. This event was also observed by the Large Angle and Spectrometric Coronagraph Experiment (LASCO) coronagraphs. WISPR and LASCO view remarkably similar structures that enable useful cross-comparison between the two data sets as well as stereoscopic imaging of the CME. An analysis is extended to lower heights by linking the white-light observations to extreme ultraviolet (EUV) data from the Atmospheric Imaging Assembly, which reveal a structure that erupts more than a fu. . .
Date: 02/2020 Publisher: The Astrophysical Journal Supplement Series Pages: 25 DOI: 10.3847/1538-4365/ab4ff0 Available at: https://iopscience.iop.org/article/10.3847/1538-4365/ab4ff0
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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: Mann Ingrid, Nouzák Libor, Vaverka Jakub, Antonsen Tarjei, Fredriksen Åshild, et al.
Title: Dust observations with antenna measurements and its prospects for observations with Parker Solar Probe and Solar Orbiter
Abstract:

The electric and magnetic field instrument suite FIELDS on board the NASA Parker Solar Probe and the radio and plasma waves instrument RPW on the ESA Solar Orbiter mission that explore the inner heliosphere are sensitive to signals generated by dust impacts. Dust impacts have been observed using electric field antennas on spacecraft since the 1980s and the method was recently used with a number of space missions to derive dust fluxes. Here, we consider the details of dust impacts, subsequent development of the impact generated plasma and how it produces the measured signals. We describe empirical approaches to characterise the signals and compare these in a qualitative discussion of laboratory simulations to predict signal shapes for spacecraft measurements in the inner solar system. Wh. . .
Date: 12/2019 Publisher: Annales Geophysicae Pages: 1121 - 1140 DOI: 10.5194/angeo-37-1121-2019 Available at: https://www.ann-geophys.net/37/1121/2019/https://www.ann-geophys.net/37/1121/2019/angeo-37-1121-2019.pdf
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Authors: Wilson Lynn B., Chen Li-Jen, Wang Shan, Schwartz Steven J., Turner Drew L., et al.
Title: Electron Energy Partition across Interplanetary Shocks. II. Statistics
Abstract:

A statistical analysis of 15,210 electron velocity distribution function (VDF) fits, observed within ±2 hr of 52 interplanetary (IP) shocks by the Wind spacecraft near 1 au, is presented. This is the second in a three-part series on electron VDFs near IP shocks. The electron velocity moment statistics for the dense, low-energy core, tenuous, hot halo, and field-aligned beam/strahl are a statistically significant list of values illustrated with both histograms and tabular lists for reference and baselines in future work. Given the large statistics in this investigation, the beam/strahl fit results in the upstream are now the most comprehensive attempt to parameterize the beam/strahl electron velocity moments in the ambient solar wind. The median density, temperature, beta, and temperatu. . .
Date: 12/2019 Publisher: The Astrophysical Journal Supplement Series Pages: 24 DOI: 10.3847/1538-4365/ab5445 Available at: https://iopscience.iop.org/article/10.3847/1538-4365/ab5445
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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: Telloni Daniele, Giordano Silvio, and Antonucci Ester
Title: On the Fast Solar Wind Heating and Acceleration Processes: A Statistical Study Based on the UVCS Survey Data
Abstract:

The UltraViolet Coronagraph Spectrometer (UVCS) on board the SOlar and Heliospheric Observatory has almost continuously observed, throughout the whole solar cycle 23, the UV solar corona. This work addresses the first-ever statistical analysis of the daily UVCS observations, performed in the O VI channel, of the northern polar coronal hole, between 1.5 and 3 R , during the period of low solar activity from 1996 April to 1997 December. The study is based on the investigation, at different heights, of the correlation between the variance of the O VI 1031.92 Å spectral line and the O VI 1031.92, 1037.61 Å doublet intensity ratio, which are proxies of the kinetic temperature of the O5+ ions and of the speed of the oxygen component of the fast solar wind, respectiv. . .
Date: 08/2019 Publisher: The Astrophysical Journal Pages: L36 DOI: 10.3847/2041-8213/ab3731 Available at: https://iopscience.iop.org/article/10.3847/2041-8213/ab3731
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Authors: Bale S. D., Badman S. T., Bonnell J. W., Bowen T. A., Burgess D., et al.
Title: Highly structured slow solar wind emerging from an equatorial coronal hole
Abstract:

During the solar minimum, when the Sun is at its least active, the solar wind is observed at high latitudes as a predominantly fast (more than 500 kilometres per second), highly Alfvénic rarefied stream of plasma originating from deep within coronal holes. Closer to the ecliptic plane, the solar wind is interspersed with a more variable slow wind of less than 500 kilometres per second. The precise origins of the slow wind streams are less certain; theories and observations suggest that they may originate at the tips of helmet streamers, from interchange reconnection near coronal hole boundaries, or within coronal holes with highly diverging magnetic fields. The heating mechanism required to drive the solar wind is also unresolved, although candidate mechanisms include Alfvé;n-wave tur. . .
Date: 12/2019 Publisher: Nature Pages: 237 - 242 DOI: 10.1038/s41586-019-1818-7 Available at: http://www.nature.com/articles/s41586-019-1818-7
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Authors: Scudder J. D.
Title: The Long-standing Closure Crisis in Coronal Plasmas
Abstract:

Coronal and solar wind physics have long used plasma fluid models to motivate physical explanations of observations; the hypothesized model is introduced into a fluid simulation to see if observations are reproduced. This procedure is called Verification of Mechanism (VoM) modeling; it is contingent on the self consistency of the closure that made the simulation possible. Inner corona VoMs typically assume weak gradient Spitzer─Braginskii closures. Four prominent coronal VoMs in place for decades are shown to contradict their closure hypotheses, demonstrably shaping coronal and solar wind research. These findings have been possible since 1953. This unchallenged evolution is worth understanding, so that similarly flawed VoMs do not continue to mislead new research. As a first step in t. . .
Date: 11/2019 Publisher: The Astrophysical Journal Pages: 148 DOI: 10.3847/1538-4357/ab48e0 Available at: https://iopscience.iop.org/article/10.3847/1538-4357/ab48e0
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