Found 12 results
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2020
Authors: Luhmann J. G., Gopalswamy N., Jian L. K., and Lugaz N.
Title: ICME Evolution in the Inner Heliosphere
Abstract:

ICMEs (interplanetary coronal mass ejections), the heliospheric counterparts of what is observed with coronagraphs at the Sun as CMEs, have been the subject of intense interest since their close association with geomagnetic storms was established in the 1980s. These major interplanetary plasma and magnetic field transients, often preceded and accompanied by solar energetic particles (SEPs), interact with planetary magnetospheres, ionospheres, and upper atmospheres in now fairly well-understood ways, although their details and context affect their overall impacts. The term ICME as it is used here refers to the complete solar-wind plasma and field disturbance, including the leading shock (if present), the compressed, deflected solar-wind plasma and the field behind the shock ("sheath"), a. . .
Date: 04/2020 Publisher: Solar Physics DOI: 10.1007/s11207-020-01624-0 Available at: http://link.springer.com/10.1007/s11207-020-01624-0
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Authors: Zhao L.-L., Zank G. P., Adhikari L., Hu Q., Kasper J. C., et al.
Title: Identification of Magnetic Flux Ropes from Parker Solar Probe Observations during the First Encounter
Abstract:

The Parker Solar Probe (PSP) observed an interplanetary coronal mass ejection (ICME) event during its first orbit around the Sun, among many other events. This event is analyzed by applying a wavelet analysis technique to obtain the reduced magnetic helicity, cross helicity, and residual energy, the first two of which are magnetohydrodynamics (MHD) invariants. Our results show that the ICME, as a large-scale magnetic flux rope, possesses high magnetic helicity, very low cross helicity, and highly negative residual energy, thus pointing to a magnetic fluctuation dominated structure. Using the same technique, we also search for small-scale coherent magnetic flux rope structures during the period from 2018 October 22 to November 21, which are intrinsic to quasi-two-dimensional MHD turbulen. . .
Date: 02/2020 Publisher: The Astrophysical Journal Supplement Series Pages: 26 DOI: 10.3847/1538-4365/ab4ff1 Available at: https://iopscience.iop.org/article/10.3847/1538-4365/ab4ff1
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Authors: Scolini C., Chané E., Pomoell J., Rodriguez L., and Poedts S.
Title: Improving Predictions of High‐Latitude Coronal Mass Ejections Throughout the Heliosphere
Abstract:

Predictions of the impact of coronal mass ejections (CMEs) in the heliosphere mostly rely on cone CME models, whose performances are optimized for locations in the ecliptic plane and at 1 AU (e.g., at Earth). Progresses in the exploration of the inner heliosphere, however, advocate the need to assess their performances at both higher latitudes and smaller heliocentric distances. In this work, we perform 3-D magnetohydrodynamics simulations of artificial cone CMEs using the EUropean Heliospheric FORecasting Information Asset (EUHFORIA), investigating the performances of cone models in the case of CMEs launched at high latitudes. We compare results obtained initializing CMEs using a commonly applied approximated (Euclidean) distance relation and using a proper (great circle) distance rela. . .
Date: 03/2020 Publisher: Space Weather DOI: 10.1029/2019SW002246 Available at: https://onlinelibrary.wiley.com/doi/abs/10.1029/2019SW002246
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Authors: Malaspina David M., Szalay Jamey R., Pokorný Petr, Page Brent, Bale Stuart D., et al.
Title: In Situ Observations of Interplanetary Dust Variability in the Inner Heliosphere
Abstract:

This work examines the variation of interplanetary dust count rates and directionality during the first three solar encounters made by the Parker Solar Probe spacecraft, covering distances between 0.65 au (∼140 solar radii, RS) and 0.16 au (∼35 RS). Dust detections are made by the FIELDS instrument via plasma clouds, produced by impact ionization of dust grains on spacecraft surfaces and resultant spacecraft potential perturbations. Dust count rates and inferred densities are found to vary by ∼50% between the three solar encounters (∼5 months per orbit), with most of the variation concentrated below 0.23 au (∼50RS). Dust count rates and directionality, as well as the encounter-to-encounter variability in both quantities are found to be consiste. . .
Date: 04/2020 Publisher: The Astrophysical Journal Pages: 115 DOI: 10.3847/1538-4357/ab799b Available at: https://iopscience.iop.org/article/10.3847/1538-4357/ab799b
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Authors: Squire J., Chandran B. D. G., and Meyrand R.
Title: In-situ Switchback Formation in the Expanding Solar Wind
Abstract:

Recent near-Sun solar-wind observations from Parker Solar Probe have found a highly dynamic magnetic environment, permeated by abrupt radial-field reversals, or "switchbacks." We show that many features of the observed turbulence are reproduced by a spectrum of Alfvénic fluctuations advected by a radially expanding flow. Starting from simple superpositions of low-amplitude outward-propagating waves, our expanding-box compressible magnetohydrodynamic simulations naturally develop switchbacks because (i) the normalized amplitude of waves grows due to expansion and (ii) fluctuations evolve toward spherical polarization (i.e., nearly constant field strength). These results suggest that switchbacks form in situ in the expanding solar wind and are not indicative of impulsive processes in the. . .
Date: 03/2020 Publisher: The Astrophysical Journal Pages: L2 DOI: 10.3847/2041-8213/ab74e1 Available at: https://iopscience.iop.org/article/10.3847/2041-8213/ab74e1
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Authors: Bowen Trevor A., Mallet Alfred, Huang Jia, Klein Kristopher G., Malaspina David M., et al.
Title: Ion-scale Electromagnetic Waves in the Inner Heliosphere
Abstract:

Understanding the physical processes in the solar wind and corona that actively contribute to heating, acceleration, and dissipation is a primary objective of NASA's Parker Solar Probe (PSP) mission. Observations of circularly polarized electromagnetic waves at ion scales suggest that cyclotron resonance and wave─particle interactions are dynamically relevant in the inner heliosphere. A wavelet-based statistical study of circularly polarized events in the first perihelion encounter of PSP demonstrates that transverse electromagnetic waves at ion resonant scales are observed in 30─50% of radial field intervals. Average wave amplitudes of approximately 4 nT are measured, while the mean duration of wave events is on the order of 20 s; however, long-duration wave events can exist withou. . .
Date: 02/2020 Publisher: The Astrophysical Journal Supplement Series Pages: 66 DOI: 10.3847/1538-4365/ab6c65 Available at: https://iopscience.iop.org/article/10.3847/1538-4365/
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Authors: Phan T. D., Bale S. D., Eastwood J. P., Lavraud B., Drake J. F., et al.
Title: Parker Solar Probe In Situ Observations of Magnetic Reconnection Exhausts during Encounter 1
Abstract:

Magnetic reconnection in current sheets converts magnetic energy into particle energy. The process may play an important role in the acceleration and heating of the solar wind close to the Sun. Observations from Parker Solar Probe (PSP) provide a new opportunity to study this problem, as it measures the solar wind at unprecedented close distances to the Sun. During the first orbit, PSP encountered a large number of current sheets in the solar wind through perihelion at 35.7 solar radii. We performed a comprehensive survey of these current sheets and found evidence for 21 reconnection exhausts. These exhausts were observed in heliospheric current sheets, coronal mass ejections, and regular solar wind. However, we find that the majority of current sheets encountered around perihelion, whe. . .
Date: 02/2020 Publisher: The Astrophysical Journal Supplement Series Pages: 34 DOI: 10.3847/1538-4365/ab55ee Available at: https://iopscience.iop.org/article/10.3847/1538-4365/ab55ee
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Authors: Battams Karl, Knight Matthew M., Kelley Michael S. P., Gallagher Brendan M., Howard Russell A., et al.
Title: Parker Solar Probe Observations of a Dust Trail in the Orbit of (3200) Phaethon
Abstract:

We present the identification and preliminary analysis of a dust trail following the orbit of (3200) Phaethon as seen in white-light images recorded by the Wide-field Imager for Parker Solar Probe (WISPR) instrument on the NASA Parker Solar Probe (PSP) mission. During PSP's first solar encounter in 2018 November, a dust trail following Phaethon's orbit was visible for several days and crossing two fields of view. Preliminary analyses indicate this trail to have a visual magnitude of 15.8 ± 0.3 per pixel and a surface brightness of 25.0 mag arcsec−2 as seen by PSP/WISPR from a distance of ̃0.2 au from the trail. We estimate the total mass of the stream to be ̃(0.4─1.3) × 1012 kg, which is consistent with, though slightly underestimates, the assumed mass of t. . .
Date: 02/2020 Publisher: The Astrophysical Journal Supplement Series Pages: 64 DOI: 10.3847/1538-4365/ab6c68 Available at: https://iopscience.iop.org/article/10.3847/1538-4365/ab6c68
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2018
Authors: Graham G. A., Rae I. J., Owen C. J., and Walsh A. P.
Title: Investigating the Effect of IMF Path Length on Pitch-angle Scattering of Strahl within 1 au
Abstract:

Strahl is the strongly field-aligned, beam-like population of electrons in the solar wind. Strahl width is observed to increase with distance from the Sun, and hence strahl electrons must be subject to in-transit scattering effects. Different energy relations have been both observed and modeled for both strahl width and the width increase with radial distance. Thus, there is much debate regarding what mechanism(s) scatter strahl. In this study, we use a novel method to investigate strahl evolution within 1 au by estimating the distance traveled by the strahl along the interplanetary magnetic field (IMF). We do this by implementing methods developed in previous studies, which make use of the onset of solar energetic particles at ̃1 au. Thus, we are able to obtain average strahl broadeni. . .
Date: 03/2018 Publisher: The Astrophysical Journal Pages: 40 DOI: 10.3847/1538-4357/aaaf1b Available at: http://stacks.iop.org/0004-637X/855/i=1/a=40?key=crossref.ef4d8c88b914db7976655ab16f8f792a
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2015
Authors: el H. ̧, Motschmann U., üchner J., Narita Y., and Nariyuki Y.
Title: ION-SCALE TURBULENCE IN THE INNER HELIOSPHERE: RADIAL DEPENDENCE
Abstract:

The evolution of the ion-scale plasma turbulence in the inner heliosphere is studied by associating the plasma parameters for hybrid-code turbulence simulations to the radial distance from the Sun via a Solar wind model based mapping procedure. Using a mapping based on a one-dimensional solar wind expansion model, the resulting ion-kinetic scale turbulence is related to the solar wind distance from the Sun. For this purpose the mapping is carried out for various values of ion beta that correspond to the heliocentric distance. It is shown that the relevant normal modes such as ion cyclotron and ion Bernstein modes will occur first at radial distances of about 0.2-0.3 AU, i.e., near the Mercury orbit. This finding can be used as a reference, a prediction to guide the in situ measurements . . .
Date: 10/2015 Publisher: The Astrophysical Journal Pages: 175 DOI: 10.1088/0004-637X/812/2/175 Available at: http://stacks.iop.org/0004-637X/812/i=2/a=175?key=crossref.a9d511ae127248e735f11254de6e3bb9
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2014
Authors: DeForest C. E., Howard T. A., and McComas D. J.
Title: INBOUND WAVES IN THE SOLAR CORONA: A DIRECT INDICATOR OF ALFVÉN SURFACE LOCATION
Abstract:

The tenuous supersonic solar wind that streams from the top of the corona passes through a natural boundary—the Alfvén surface—that marks the causal disconnection of individual packets of plasma and magnetic flux from the Sun itself. The Alfvén surface is the locus where the radial motion of the accelerating solar wind passes the radial Alfvén speed, and therefore any displacement of material cannot carry information back down into the corona. It is thus the natural outer boundary of the solar corona and the inner boundary of interplanetary space. Using a new and unique motion analysis to separate inbound and outbound motions in synoptic visible-light image sequences from the COR2 coronagraph on board the STEREO-A spacecraft, we have identified inbound wave motion in the outer co. . .
Date: 06/2014 Publisher: The Astrophysical Journal Pages: 124 DOI: 10.1088/0004-637X/787/2/124 Available at: http://stacks.iop.org/0004-637X/787/i=2/a=124?key=crossref.8ca79a982204ddd2b4922cc108364616
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Authors: McComas D. J., Alexander N., Angold N., Bale S., Beebe C., et al.
Title: Integrated Science Investigation of the Sun (ISIS): Design of the Energetic Particle Investigation
Abstract:

The Integrated Science Investigation of the Sun (ISIS) is a complete science investigation on the Solar Probe Plus (SPP) mission, which flies to within nine solar radii of the Sun’s surface. ISIS comprises a two-instrument suite to measure energetic particles over a very broad energy range, as well as coordinated management, science operations, data processing, and scientific analysis. Together, ISIS observations allow us to explore the mechanisms of energetic particles dynamics, including their: (1) Origins—defining the seed populations and physical conditions necessary for energetic particle acceleration; (2) Acceleration—determining the roles of shocks, reconnection, waves, and turbulence in accelerating energetic particles; and (3) Transport—revealing how ener. . .
Date: 07/2014 Publisher: Space Science Reviews DOI: 10.1007/s11214-014-0059-1 Available at: http://link.springer.com/content/pdf/10.1007/s11214-014-0059-1
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