Found 14 results
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2020
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: Halekas J. S., Whittlesey P., Larson D. E., McGinnis D., Maksimovic M., et al.
Title: Electrons in the Young Solar Wind: First Results from the Parker Solar Probe
Abstract:

The Solar Wind Electrons Alphas and Protons experiment on the Parker Solar Probe (PSP) mission measures the three-dimensional electron velocity distribution function. We derive the parameters of the core, halo, and strahl populations utilizing a combination of fitting to model distributions and numerical integration for ̃100,000 electron distributions measured near the Sun on the first two PSP orbits, which reached heliocentric distances as small as ̃0.17 au. As expected, the electron core density and temperature increase with decreasing heliocentric distance, while the ratio of electron thermal pressure to magnetic pressure (βe) decreases. These quantities have radial scaling consistent with previous observations farther from the Sun, with superposed variations associated. . .
Date: 02/2020 Publisher: The Astrophysical Journal Supplement Series Pages: 22 DOI: 10.3847/1538-4365/ab4cec Available at: https://iopscience.iop.org/article/10.3847/1538-4365/ab4cec
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Authors: Cohen C. M. S., Christian E. R., Cummings A. C., Davis A. J., Desai M. I., et al.
Title: Energetic Particle Increases Associated with Stream Interaction Regions
Abstract:

The Parker Solar Probe was launched on 2018 August 12 and completed its second orbit on 2019 June 19 with perihelion of 35.7 solar radii. During this time, the Energetic Particle Instrument-Hi (EPI-Hi, one of the two energetic particle instruments comprising the Integrated Science Investigation of the Sun, IS☉IS) measured seven proton intensity increases associated with stream interaction regions (SIRs), two of which appear to be occurring in the same region corotating with the Sun. The events are relatively weak, with observed proton spectra extending to only a few MeV and lasting for a few days. The proton spectra are best characterized by power laws with indices ranging from -4.3 to -6.5, generally softer than events associated with SIRs observed at 1 au and beyond. Helium spectra . . .
Date: 02/2020 Publisher: The Astrophysical Journal Supplement Series Pages: 20 DOI: 10.3847/1538-4365/ab4c38 Available at: https://iopscience.iop.org/article/10.3847/1538-4365/ab4c38
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Authors: Lavraud B., Fargette N., Réville V., Szabo A., Huang J., et al.
Title: The Heliospheric Current Sheet and Plasma Sheet during Parker Solar Probe’s First Orbit
Abstract:

We present heliospheric current sheet (HCS) and plasma sheet (HPS) observations during Parker Solar Probe’s (PSP) first orbit around the Sun. We focus on the eight intervals that display a true sector boundary (TSB; based on suprathermal electron pitch angle distributions) with one or several associated current sheets. The analysis shows that (1) the main density enhancements in the vicinity of the TSB and HCS are typically associated with electron strahl dropouts, implying magnetic disconnection from the Sun, (2) the density enhancements are just about twice that in the surrounding regions, suggesting mixing of plasmas from each side of the HCS, (3) the velocity changes at the main boundaries are either correlated or anticorrelated with magnetic field changes, consistent with magneti. . .
Date: 05/2020 Publisher: The Astrophysical Journal Pages: L19 DOI: 10.3847/2041-8213/ab8d2d Available at: https://iopscience.iop.org/article/10.3847/2041-8213/ab8d2d
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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: Verniero J. L., Larson D. E., Livi R., Rahmati A., McManus M. D., et al.
Title: Parker Solar Probe Observations of Proton Beams Simultaneous with Ion-scale Waves
Abstract:

Parker Solar Probe (PSP), NASA’s latest and closest mission to the Sun, is on a journey to investigate fundamental enigmas of the inner heliosphere. This paper reports initial observations made by the Solar Probe Analyzer for Ions (SPAN-I), one of the instruments in the Solar Wind Electrons Alphas and Protons instrument suite. We address the presence of secondary proton beams in concert with ion-scale waves observed by FIELDS, the electromagnetic fields instrument suite. We show two events from PSP’s second orbit that demonstrate signatures consistent with wave-particle interactions. We showcase 3D velocity distribution functions (VDFs) measured by SPAN-I during times of strong wave power at ion scales. From an initial instability analysis, we infer that the VDFs departed far enough. . .
Date: 05/2020 Publisher: The Astrophysical Journal Supplement Series Pages: 5 DOI: 10.3847/1538-4365/ab86af Available at: https://iopscience.iop.org/article/10.3847/1538-4365/ab86afhttps
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Authors: Kim T. K., Pogorelov N. V., Arge C. N., Henney C. J., Jones-Mecholsky S. I., et al.
Title: Predicting the Solar Wind at the Parker Solar Probe Using an Empirically Driven MHD Model
Abstract:

Since its launch on 2018 August 12, Parker Solar Probe (PSP) has completed its first and second orbits around the Sun, having reached down to 35.7 solar radii at each perihelion. In anticipation of the exciting new data at such unprecedented distances, we have simulated the global 3D heliosphere using an MHD model coupled with a semi-empirical coronal model using the best available photospheric magnetograms as input. We compare our heliospheric MHD simulation results with in situ measurements along the PSP trajectory from its launch to the completion of the second orbit, with particular emphasis on the solar wind structure around the first two solar encounters. Furthermore, we show our model prediction for the third perihelion, which occurred on 2019 September 1. Comparison of the MHD r. . .
Date: 02/2020 Publisher: The Astrophysical Journal Supplement Series Pages: 40 DOI: 10.3847/1538-4365/ab58c9 Available at: https://iopscience.iop.org/article/10.3847/1538-4365/ab58c9
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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 soft en. . .
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: 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 Advanced C. . .
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: 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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2019
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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2013
Authors: Case A. W., Kasper J. C., Daigneau P. S., Caldwell D., Freeman M., et al.
Title: AIP Conference ProceedingsDesigning a sun-pointing Faraday cup for solar probe plus
Abstract:

The NASA Solar Probe Plus (SPP) mission will be the first spacecraft to pass through the sub-Alfvénic solar corona. The objectives of the mission are to trace the flow of energy that heats and accelerates the solar corona and solar wind, to determine the structure and dynamics of the plasma and magnetic fields at the sources of the solar wind, and to explore mechanisms that accelerate and transport energetic particles. The Solar Wind Electrons, Alphas, and Protons (SWEAP) Investigation instrument suite on SPP will measure the bulk solar wind conditions in the inner heliosphere. SWEAP consists of the Solar Probe Cup (SPC), a sun-pointing Faraday Cup, and the Solar Probe ANalyzers (SPAN), a set of 3 electrostatic analyzers that will reside in the penumbra of SPP’s thermal protection sy. . .
Date: Publisher: AIP DOI: 10.1063/1.4811083 Available at: http://scitation.aip.org/content/aip/proceeding/aipcp/10.1063/1.4811083
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2010
Authors: Ergun R. E., Malaspina D. M., Bale S. D., McFadden J. P., Larson D. E., et al.
Title: Spacecraft charging and ion wake formation in the near-Sun environment
Abstract:

A three-dimensional, self-consistent code is employed to solve for the static potential structure surrounding a spacecraft in a high photoelectron environment. The numerical solutions show that, under certain conditions, a spacecraft can take on a negative potential in spite of strong photoelectron currents. The negative potential is due to an electrostatic barrier near the surface of the spacecraft that can reflect a large fraction of the photoelectron flux back to the spacecraft. This electrostatic barrier forms if (1) the photoelectron density at the surface of the spacecraft greatly exceeds the ambient plasma density, (2) the spacecraft size is significantly larger than local Debye length of the photoelectrons, and (3) the thermal electron energy is much larger than the characterist. . .
Date: 07/2010 Publisher: Physics of Plasmas Pages: 072903 DOI: 10.1063/1.3457484 Available at: http://aip.scitation.org/doi/10.1063/1.3457484http://aip.scitation.org/doi/pdf/10.1063/1.3457484
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