Parker Solar Probe Bibliography

2020

<p>Heat transport in the solar corona and wind is still a major unsolved astrophysical problem. Because of the key role played by electrons, the electron density and temperature(s) are important prerequisites for understanding these plasmas. We present such in situ measurements along the two first solar encounters of the Parker Solar Probe, between 0.5 and 0.17 au from the Sun, revealing different states of the emerging solar wind near the solar activity minimum. These preliminary results are obtained from a simplified analysis of the plasma quasi-thermal noise (QTN) spectrum measured by the Radio Frequency Spectrometer (FIELDS). The local electron density is deduced from the tracking of the plasma line, which enables accurate measurements, independent of calibrations and spacecraft perturbations, whereas the temperatures of the thermal and suprathermal components of the velocity distribution, as well as the average kinetic temperature, are deduced from the shape of the plasma…
2020


<p>This Letter explores the relevance of nanoflare-based models for heating the quiet Sun corona. Using meterwave data from the Murchison Widefield Array, we present the first successful detection of impulsive emissions down to flux densities of \~mSFU, about two orders of magnitude weaker than earlier attempts. These impulsive emissions have durations ≲1 s and are present throughout the quiet solar corona. The fractional time occupancy of these impulsive emissions at a given region is ≲10\%. The histograms of these impulsive emissions follow a power-law distribution and show signs of clustering at small timescales. Our estimate of the energy that must be dumped in the corona to generate these impulsive emissions is consistent with the coronal heating requirements. Additionally, the statistical properties of these impulsive emissions are very similar to those recently determined for magnetic switchbacks by the Parker Solar Probe (PSP). We hope that this work will lead to a…
2020


<p>The global circulation of the open magnetic flux of the Sun, the component of the solar magnetic field that opens into the heliosphere, and the consequences of the global circulation were proposed by Fisk and coworkers in the early 2000s. The Parker Solar Probe, on its initial encounters with the Sun, has provided direct confirmation of both the global circulation and the physical mechanism by which the circulation occurs, transport by interchange reconnection between open magnetic flux and large coronal loops. The implications of this confirmation of the global circulation of open magnetic flux and the importance of interchange reconnection is discussed.</p>
2020


<p>We present heliospheric current sheet (HCS) and plasma sheet (HPS) observations during Parker Solar Probe\textquoterights (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 magnetic reconnection, (4) there often exists a layer of disconnected magnetic field just outside the high-density regions, in agreement with a reconnected topology, (5) while a few cases…
2020


<p>The Parker Solar Probe (PSP) completed its first solar encounter in 2018 November, bringing it closer to the Sun than any previous mission. This allowed in situ investigation of the heliospheric current sheet (HCS) inside the orbit of Venus. The Parker observations reveal a well defined magnetic sector structure placing the spacecraft in a negative polarity region for most of the encounter. The observed current sheet crossings are compared to the predictions of both potential field source surface and magnetohydrodynamic models. All the model predictions are in good qualitative agreement with the observed crossings of the HCS. The models also generally agree that the HCS was nearly parallel with the solar equator during the inbound leg of the encounter and more significantly inclined during the outbound portion. The current sheet crossings at PSP are also compared to similar measurements made by the Wind spacecraft near Earth at 1 au. After allowing for orbital geometry and…
2020


<p>Alfv\ enic fluctuations in solar wind are an intrinsic property of fast streams, while slow intervals typically have a very low degree of Alfv\ enicity, with much more variable parameters. However, sometimes a slow wind can be highly Alfv\ enic. Here we compare three different regimes of solar wind, in terms of Alfv\ enic content and spectral properties, during a minimum phase of the solar activity and at 0.3 au. We show that fast and Alfv\ enic slow intervals share some common characteristics. This would suggest a similar solar origin, with the latter coming from over-expanded magnetic field lines, in agreement with observations at 1 au and at the maximum of the solar cycle. Due to the Alfv\ enic nature of the fluctuations in both fast and Alfv\ enic slow winds, we observe a well-defined correlation between the flow speed and the angle between magnetic field vector and radial direction. The high level of Alfv\ enicity is also responsible of intermittent enhancements (i.e.…
2020


<p>The nature of the plasma wave modes around the ion kinetic scales in highly Alfv\ enic slow solar wind turbulence is investigated using data from the NASA\textquoterights Parker Solar Probe taken in the inner heliosphere, at 0.18 au from the Sun. The joint distribution of the normalized reduced magnetic helicity σ<sub>m</sub> (θ<sub>RB</sub>, τ) is obtained, where θ<sub>RB</sub> is the angle between the local mean magnetic field and the radial direction and τ is the temporal scale. Two populations around ion scales are identified: the first population has σ<sub>m</sub> (θ<sub>RB</sub>, τ) \&lt; 0 for frequencies (in the spacecraft frame) ranging from 2.1 to 26 Hz for 60\textdegree \&lt; θ<sub>RB</sub> \&lt; 130\textdegree, corresponding to kinetic Alfv\ en waves (KAWs), and the second population has σ<sub>m</sub> (θ<sub>RB</sub>, τ) \&gt; 0 in the frequency range [1…
2020


<p>In this work, we present the first results from the flux angle (FA) operation mode of the Faraday Cup instrument on board the Parker Solar Probe (PSP). The FA mode allows rapid measurements of phase space density fluctuations close to the peak of the proton velocity distribution function with a cadence of 293 Hz. This approach provides an invaluable tool for understanding kinetic-scale turbulence in the solar wind and solar corona. We describe a technique to convert the phase space density fluctuations into vector velocity components and compute several turbulence parameters, such as spectral index, residual energy, and cross helicity during two intervals when the FA mode was used in PSP\textquoterights first encounter at 0.174 au distance from the Sun.</p>
2020


<p>Electric field spectra measured on the\&nbsp;Parker\&nbsp;Solar\&nbsp;Probe\&nbsp;typically contain upwards of 1000 large-amplitude (similar to 15 mV m(-1)), wideband (similar to 100-15,000 Hz), few-second-duration, electric field waveforms per day. The satellite also collected about 85 three-second bursts of electric field waveforms per day at a data rate of similar to 150,000 samples per second. Eight such bursts caught these waves, all of which were located in switchbacks of the magnetic field. A wave burst on 2019 September 7, when the spacecraft was at an altitude of 55\&nbsp;solar\&nbsp;radii, is described. It contained Doppler-shifted ion acoustic waves that propagated in the direction opposite to the local magnetic field at all rest-frame frequencies from 60 Hz to nearly the proton plasma frequency of 2200 Hz, while no other wave modes were present. The eight bursts all contained ion acoustic waves whose individual net potentials were \&lt…
2020


<p>One of the discoveries of the Parker Solar Probe during its first encounters with the Sun is ubiquitous presence of relatively small-scale structures standing out as sudden deflections of the magnetic field. They were named "switchbacks" since some of them show a full reversal of the radial component of the magnetic field and then return to "regular" conditions. We carried out an analysis of three typical switchback structures having different characteristics: I. Alfv\ enic structure, where the variations of the magnetic field components take place while conserving the magnitude of the magnetic field; II. Compressional structure, where the magnitude of the field varies together with changes of its components; and III. Structure manifesting full reversal of the magnetic field, presumably Alfv\ en, which is an extremal example of a switchback. We analyzed the properties of the magnetic fields of these structures and of their boundaries. Observations and…
2020


<p>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\textquoterights first observations of the heliospheric magnetic field from ̃0.5 au (107.5 R<sub>☉</sub>) down to 0.16 au (35.7 R<sub>☉</sub>). 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 speed instead of assuming it to be constant with longitude and latitude. We also explore the source surface height parameter (R<sub>SS</sub>) to the…
2020


<p>During Parker Solar Probe\textquoterights first close encounter with the Sun in early 2018 November, a large number of impulsive rotations in the magnetic field were detected within 50 R<sub>s</sub>; these also occurred in association with short-lived impulsive solar wind bursts in speed. These impulsive features are now called "switchback" events. We examined a set of these switchbacks where the boundary transition into and out of the switchback was abrupt, with fast B rotations and simultaneous solar wind speed changes occurring on timescales of less than \~10 s; these thus appear as step function-like changes in the radial component of B and V. Our objective was to search for any diamagnetic effects that might occur especially if the boundaries are associated with quick changes in density (i.e., a steep spatial density gradient at the switchback boundary). We identified 25 switchback entries where the radial component of B, B<sub>r</sub>,…
2020


<p>Parker Solar Probe (PSP) observations during its first encounter at 35.7 R<sub>☉</sub> 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 Alfv\ en 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 evolution of such large amplitude Alfv\ enic fluctuations by including, in agreement with observations, both a radial magnetic field inversion and an initially constant total magnetic…
2020


<p>The solar wind shows periods of highly Alfv\ enic activity, where velocity fluctuations and magnetic fluctuations are aligned or antialigned with each other. It is generally agreed that solar wind plasma velocity and magnetic field fluctuations observed by the Parker Solar Probe (PSP) during the first encounter are mostly highly Alfv\ enic. However, quantitative measures of Alfv\ enicity are needed to understand how the characterization of these fluctuations compares with standard measures from prior missions in the inner and outer heliosphere, in fast wind and slow wind, and at high and low latitudes. To investigate this issue, we employ several measures to quantify the extent of Alfv\ enicity\textemdashthe Alfv\ en ratio r<sub>A</sub>, the normalized cross helicity σ<sub>c</sub>, the normalized residual energy σ<sub>r</sub>, and the cosine of angle between velocity and magnetic fluctuations cos<em>θ</em>\&nbsp;<em>v…
2020


<p>NASA\textquoterights Parker Solar Probe (PSP) mission is currently investigating the local plasma environment of the inner heliosphere (\&lt;0.25 R<sub>☉</sub>) using both in situ and remote sensing instrumentation. Connecting signatures of microphysical particle heating and acceleration processes to macroscale heliospheric structure requires sensitive measurements of electromagnetic fields over a large range of physical scales. The FIELDS instrument, which provides PSP with in situ measurements of electromagnetic fields of the inner heliosphere and corona, includes a set of three vector magnetometers: two fluxgate magnetometers (MAGs) and a single inductively coupled search-coil magnetometer (SCM). Together, the three FIELDS magnetometers enable measurements of the local magnetic field with a bandwidth ranging from DC to 1 MHz. This manuscript reports on the development of a merged data set combining SCM and MAG (SCaM) measurements, enabling a high fidelity…
2020


<p>We present model calculations of the transport processes of solar energetic particles in the corona and interplanetary medium for two events detected by Parker Solar Probe near its second perihelion on 2019 April 2 and April 4. In the 2019 April 2 event, the \&lt;100 keV proton differential intensity measured by the Integrated Science Investigation of the Sun Low-Energy Energetic Particle instrument increased by more than a factor of 10 above the pre-event intensity, whereas the \~1 MeV proton differential intensity detected by the High-Energy Energetic Particle Instrument did not show any intensity enhancement. In the 2019 April 4 event, the \~1 MeV proton intensity showed an increase of more than a factor of 100 above the pre-event intensity, but the \&lt;100 keV proton intensity enhancement was rather low and gradual. The observational fact that only the 2019 April 4 event displayed a high-energy intensity enhancement indicates that the associated acceleration…
2020


<p>On 2018 November 5, about 24 hr before the first close perihelion passage of Parker Solar Probe (PSP), a coronal mass ejection (CME) entered the field of view of the inner detector of the Wide-field Imager for Solar PRobe (WISPR) instrument on board PSP, with the northward component of its trajectory carrying the leading edge of the CME off the top edge of the detector about four hours after its first appearance. We connect this event to a very small jetlike transient observed from 1 au by coronagraphs on both the SOlar and Heliospheric Observatory (SOHO) and the A component of the Solar TErrestrial RElations Observatory mission (STEREO-A). This allows us to make the first three-dimensional reconstruction of a CME structure considering both observations made very close to the Sun and images from two observatories at 1 au. The CME may be small and jetlike as viewed from 1 au, but the close-in vantage point of PSP/WISPR demonstrates that it is not intrinsically jetlike but…
2020


<p>The Parker Solar Probe (PSP) spacecraft has flown into the densest, previously unexplored, innermost region of our solar system\textquoterights zodiacal cloud. While PSP does not have a dedicated dust detector, multiple instruments on the spacecraft are sensitive to the effects of meteoroid bombardment. Here, we discuss measurements taken during PSP\textquoterights second orbit and compare them to models of the zodiacal cloud\textquoterights dust distribution. Comparing the radial impact rate trends and the timing and location of a dust impact to an energetic particle detector, we find the impactor population to be consistent with dust grains on hyperbolic orbits escaping the solar system. Assuming PSP\textquoterights impact environment is dominated by hyperbolic impactors, the total quantity of dust ejected from our solar system is estimated to be 0.5-10 tons/s. We expect PSP will encounter an increasingly intense impactor environment as its perihelion distance and semimajor…
2020


<p>The solar wind nonradial velocity components observed beyond the Alfv\ en point are usually attributed to waves, the interaction of different streams, or other transient phenomena. However, Earth-orbiting spacecraft as well as monitors at L1 indicate systematic deviations of the wind velocity from the radial direction. Since these deviations are of the order of several degrees, the calibration of the instruments is often questioned. This paper investigates for the first time the evolution of nonradial components of the solar wind flow along the path from ≍0.17 to 10 au. A comparison of observations at 1 au with those closer to or farther from the Sun based on measurements of many spacecraft at different locations in the heliosphere (Parker Solar Probe, Helios 1 and 2, Wind, Advanced Composition Explorer, Spektr-R, Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon\textquoterights Interaction with the Sun (ARTEMIS) probes, Mars Atmosphere and Volatile…
2020


<p>Conclusively determining the states of the solar wind will aid in tracing the origins of those states to the Sun, and in the process help to find the wind\textquoterights origin and acceleration mechanism(s). Prior studies have characterized the various states of the wind, making lists that are only partially based on objective criteria; different approaches obtain substantially different results. To uncover the unbiased states of the solar wind, we use "k-means clustering"\textemdashan unsupervised machine learning method\textemdashincluding constructed multipoint variables. The method allows exploration of different descriptive state variables and numbers of fundamental states (clusters). We show that the clusters reveal structures similar to those found by more ad hoc means, including coronal hole wind, interplanetary coronal mass ejections, "slow wind" (better: noncoronal hole flow), "pseudostreamers," and stream interaction regions, but with…
2020


<p>Observations at 1 au have confirmed that enhancements in measured energetic-particle (EP) fluxes are statistically associated with "rough" magnetic fields, i.e., fields with atypically large spatial derivatives or increments, as measured by the Partial Variance of Increments (PVI) method. One way to interpret this observation is as an association of the EPs with trapping or channeling within magnetic flux tubes, possibly near their boundaries. However, it remains unclear whether this association is a transport or local effect; i.e., the particles might have been energized at a distant location, perhaps by shocks or reconnection, or they might experience local energization or re-acceleration. The Parker Solar Probe (PSP), even in its first two orbits, offers a unique opportunity to study this statistical correlation closer to the corona. As a first step, we analyze the separate correlation properties of the EPs measured by the Integrated Science Investigation of the…
2020


<p>The solar wind proton temperature at 1 au has been found to be correlated with small-scale intermittent magnetic structures, i.e., regions with enhanced temperature are associated with coherent structures, such as current sheets. Using Parker Solar Probe data from the first encounter, we study this association using measurements of the radial proton temperature, employing the partial variance of increments (PVI) technique to identify intermittent magnetic structures. We observe that the probability density functions of high PVI events have higher median temperatures than those with lower PVI. The regions in space where PVI peaks were also locations that had enhanced temperatures when compared with similar regions, suggesting a heating mechanism in the young solar wind that is associated with intermittency developed by a nonlinear turbulent cascade in the immediate vicinity.</p>
2020


<p>A solar energetic particle event was detected by the Integrated Science Investigation of the Sun (IS☉IS) instrument suite on Parker Solar Probe (PSP) on 2019 April 4 when the spacecraft was inside of 0.17 au and less than 1 day before its second perihelion, providing an opportunity to study solar particle acceleration and transport unprecedentedly close to the source. The event was very small, with peak 1 MeV proton intensities of ̃0.3 particles (cm<sup>2</sup> sr s MeV)<sup>-1</sup>, and was undetectable above background levels at energies above 10 MeV or in particle detectors at 1 au. It was strongly anisotropic, with intensities flowing outward from the Sun up to 30 times greater than those flowing inward persisting throughout the event. Temporal association between particle increases and small brightness surges in the extreme-ultraviolet observed by the Solar TErrestrial RElations Observatory, which were also accompanied by type III radio emission…
2020


<p>Parker Solar Probe (PSP), NASA\textquoterights 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\textquoterights 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 away from local thermodynamic equilibrium to provide sufficient free energy to locally generate waves. These events exemplify the types of instabilities that may be…
2020


<p>Microinstabilities and waves excited at moderate-Mach-number perpendicular shocks in the near-Sun solar wind are investigated by full particle-in-cell simulations. By analyzing the dispersion relation of fluctuating field components directly issued from the shock simulation, we obtain key findings concerning wave excitations at the shock front: (1) at the leading edge of the foot, two types of electrostatic (ES) waves are observed. The relative drift of the reflected ions versus the electrons triggers an electron cyclotron drift instability (ECDI) that excites the first ES wave. Because the bulk velocity of gyro-reflected ions shifts to the direction of the shock front, the resulting ES wave propagates oblique to the shock normal. Immediately, a fraction of incident electrons are accelerated by this ES wave and a ring-like velocity distribution is generated. They can couple with the hot Maxwellian core and excite the second ES wave around the upper hybrid frequency. (2) From…
2020


<p>Electric fields are generally measured or calculated using two intuitive assumptions: (1) the electric field equals the voltage divided by the antenna length when the antenna is electromagnetically short (2) the antenna responds best to electric field along its length. Both assumptions are often incorrect for electrostatic fields because they scale as the Debye length or as the electron gyroradius, which may be smaller than the antenna length. Taking into account this little-known fact enables us to complete or correct several recent papers on plasma spontaneous fluctuations in various solar system environments.</p>
2020


<p>Data from the first two orbits of the Sun by Parker Solar Probe reveal that the solar wind sunward of 50 solar radii is replete with plasma waves and instabilities. One of the most prominent plasma wave power enhancements in this region appears near the electron cyclotron frequency (f<sub>ce</sub>). Most of this wave power is concentrated in electric field fluctuations near 0.7 f<sub>ce</sub> and f<sub>ce</sub>, with strong harmonics of both frequencies extending above f<sub>ce</sub>. At least two distinct, often concurrent, wave modes are observed, preliminarily identified as electrostatic whistler-mode waves and electron Bernstein waves. Wave intervals range in duration from a few seconds to hours. Both the amplitudes and number of detections of these near-f<sub>ce</sub> waves increase significantly with decreasing distance to the Sun, suggesting that they play an important role in the evolution of electron…
2020


<p>A polytropic process describes the transition of a fluid from one state to another through a specific relationship between the fluid density and temperature. The value of the polytropic index that governs this relationship determines the heat transfer and the effective degrees of freedom during a specific process. In this study, we analyze\&nbsp;solar\&nbsp;wind proton plasma measurements, obtained by the Faraday cup instrument on board the\&nbsp;Parker\&nbsp;Solar\&nbsp;Probe. We examine the large-scale variations of the proton plasma density and temperature within the inner heliosphere explored by the spacecraft. We then address the polytropic behavior in the density and temperature fluctuations in short time intervals, which we analyze in order to derive the effective polytropic index of small-scale processes. The large-scale variations of the\&nbsp;solar\&nbsp;wind proton density and temperature, which are associated with the plasma expansion…
2020


<p>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 results with PSP observations provides new insights into solar wind acceleration. Moreover, PSP observations reveal how accurately the Air Force Data Assimilative Photospheric flux Transport-…
2020


<p>In October 2017, the first interstellar object within our solar system was discovered. Today designated 1I/\textquoterightOumuamua, it shows characteristics that have never before been observed in a celestial body. Due to these characteristics, an in-situ investigation of 1I would be of extraordinary scientific value. Previous studies have demonstrated that a mission to 1I/\textquoterightOumuamua is feasible using current and near-term technologies, however, with an anticipated launch date of 2020-2021. This is too soon to be realistic. This paper aims at addressing the question of the feasibility of a mission to 1I/\textquoterightOumuamua in 2024 and beyond. Using the OITS trajectory simulation tool, various scenarios are analyzed, including a powered Jupiter flyby and Solar Oberth maneuver, a Jupiter powered flyby, and more complex schemes including a Mars and Venus flyby. With a powered Jupiter flyby and Solar Oberth maneuver, we identify a trajectory to 1I/\…
2020


<p>Solar Probe Cup (SPC) is a Faraday cup instrument on board NASA\textquoterights 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<sup>-1</sup>). It also measures electrons with an energy/charge between 100 and 1500 V. SPC has been designed to have a wide dynamic range that is capable of measuring protons and alpha particles at the closest perihelion (9.86 solar radii…
2020


<p>he long-term evolution of the Sun\textquoterights rotation period cannot be directly observed, and is instead inferred from trends in the measured rotation periods of other Sun-like stars. Assuming the Sun spins down as it ages, following rotation rate proportional to age(-1/2), requires the current\&nbsp;solar\&nbsp;angular momentum (AM) loss rate to be around 6 x 10(30)erg. Magnetohydrodynamic models, and previous observations of the\&nbsp;solar\&nbsp;wind (from the Helios and Wind spacecraft), generally predict a values closer to 1 x 10(30)erg or 3 x 10(30)erg, respectively. Recently, the\&nbsp;Parker\&nbsp;Solar\&nbsp;Probe\&nbsp;(PSP) observed tangential\&nbsp;solar\&nbsp;wind speeds as high as similar to 50 km s(-1)in a localized region of the inner heliosphere. If such rotational flows were prevalent throughout the corona, it would imply that the\&nbsp;solar\&nbsp;wind AM-loss rate is an order of magnitude larger than all…
2020


<p>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 contextualize the inner heliospheric conditions during the first orbit of PSP. Additionally, we determine which of these fast streams are associated with an SIR and characterize the SIR properties for…
2020


<p>In the first orbit of the Parker Solar Probe (PSP), in situ thermal plasma and magnetic field measurements were collected as close as 35 R<sub>Sun</sub> 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<sup>-1</sup>) 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 streamer formed between the northern polar coronal hole and a mid-latitude coronal hole. Using the YGUAZU-A model, the propagation of the CME is traced from the source at the…
2020


<p>Parker Solar Probe (PSP) observed a large variety of Alfv\ enic fluctuations in the fast and slow solar wind flow during its two perihelia. The properties of Alfv\ enic solar wind turbulence have been studied for decades in the near-Earth environment. A spectral index of -5/3 or -2 for magnetic field fluctuations has been observed using spacecraft measurements, which can be explained by turbulence theories of nearly incompressible magnetohydrodynamics (NI MHD) or critical balance. In this study, a rigorous search of field-aligned solar wind is applied to PSP measurements for the first time, which yields two events in the apparently slow solar wind. The parallel spectra of the magnetic fluctuations in the inertial range show a <em>k</em>\&nbsp;-5/3\&nbsp;||\&nbsp;\&nbsp;k||-5/3 power law. Probability distributions of the magnetic field show that these events are not contaminated by intermittent structures, which, according to previous studies, are…
2020


<p>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 polarization of 0.15-0.38 in the range from 8 to 12 MHz. The degree of polarization can be explained either by depolarization of initially 100\% polarized o-mode emission or by direct generation of…
2020


<p>The distribution of spacecraft in the inner heliosphere during 2019 March enabled comprehensive observations of an interplanetary coronal mass ejection (ICME) that encountered Parker Solar Probe (PSP) at 0.547 au from the Sun. This ICME originated as a slow (\~311 km s<sup>-1</sup>) streamer blowout (SBO) on the Sun as measured by the white-light coronagraphs on board the Solar TErrestrial RElations Observatory-A and the Solar and Heliospheric Observatory. Despite its low initial speed, the passage of the ICME at PSP was preceded by an anisotropic, energetic (≲100 keV/n) ion enhancement and by two interplanetary shocks. The ICME was embedded between slow (\~300 km s<sup>-1</sup>) solar wind and a following, relatively high-speed (\~500 km s<sup>-1</sup>), stream that most likely was responsible for the unexpectedly short (based on the SBO speed) ICME transit time of less than \~56 hr between the Sun and PSP, and for the formation of the…
2020


<p>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 f<sub>ce</sub> (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 f<sub>ce</sub>). 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 than what is observed at 1 au. Recent numerical studies show that such waves may potentially play a key role in breaking the heat flux and scattering the Strahl…
2020


<p>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 \&nbsp;3\&nbsp;He\&nbsp;3He -rich solar energetic particle (SEP) events under very quiet solar minimum conditions. On 2019-110-111 (April 20-21), \&nbsp;3\&nbsp;He\&nbsp;3He -rich SEPs were observed at energies near 1 MeV nucleon<sup>-1</sup> 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 Composition Explorer (ACE) spacecraft located near Earth, 0.99 au from the Sun. At that time, PSP and ACE were both magnetically connected to locations…
2020


<p>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 higher frequencies. These results suggest that outside of these structures we are in the presence of lower-amplitude fluctuations with a shorter turbulent inertial range. We conjecture that these…
2020


<p>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))<sup>2</sup>. The solar wind flow inside switchbacks was faster than that outside due to the frozen-in ions moving with the magnetic structure at the Alfv\ en speed. This energy gain results from the divergence of the Poynting flux from outside to inside the switchback, which produces a loss of electromagnetic energy on switchback entry and recovery of that energy on exit, with the…
2020


<p>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\textemdashakin to what is observed in closed coronal loops\textemdashthe 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 corona to reproduce realistic configurations and outflows surrounding the HCS. We find that this process is able to explain long (\~10-20 hr) and short (\~1-2 hr) timescales of…
2020


<p>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<sup>-1</sup>. 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 events which, after correcting for the detection efficiency, resulted in an estimated 500-1000 TDS events on this day. The TDS electric fields were bipolar, as expected for electron…
2020


<p>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<sub>☉</sub>). Here, we study the evolution of fully developed turbulence associated with the slow solar wind along the PSP trajectory between 35.55 R<sub>☉</sub> and 131.64 R<sub>☉</sub> 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<sub>☉</sub> and 131.64 R<sub>☉</sub>. The evolution of the PSP derived turbulent quantities are compared to the numerical solutions of the nearly incompressible magnetohydrodynamic (NI MHD)…
2020


<p>Context. The launch of\&nbsp;Parker\&nbsp;Solar\&nbsp;Probe\&nbsp;(PSP) in 2018, followed by\&nbsp;Solar\&nbsp;Orbiter (SO) in February 2020, has opened a new window in the exploration of\&nbsp;solar\&nbsp;magnetic activity and the origin of the heliosphere. These missions, together with other space observatories dedicated to\&nbsp;solar\&nbsp;observations, such as the\&nbsp;Solar\&nbsp;Dynamics Observatory, Hinode, IRIS, STEREO, and SOHO, with complementary in situ observations from WIND and ACE, and ground based multi-wavelength observations including the DKIST observatory that has just seen first light, promise to revolutionize our understanding of the\&nbsp;solar\&nbsp;atmosphere and of\&nbsp;solar\&nbsp;activity, from the generation and emergence of the Sun\textquoterights magnetic field to the creation of the\&nbsp;solar\&nbsp;wind and the acceleration of\&nbsp;solar\&nbsp;energetic…
2020


<p>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\textemdashRutherford 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 than to leave the Solar System? Why does it take more than one gravity assist to achieve this, and why does it require seven? Would it be more effective to use Mercury instead of Venus?…
2020


<p>Detection of the solar wind speed near the Sun is significant in understanding the heating and acceleration of the solar wind. Cometary plasma tails have long been used as natural probes for solar wind speed; previous solar wind speed estimates via plasma tails, however, were based on comet images from a single viewpoint, and the projection effect may influence the result. Using stereoscopic observations from the Solar Terrestrial Relations Observatory and the Solar and Heliospheric Observatory, we three-dimensionally reconstruct the plasma tails of three comets C/2012 S1 (ISON), C/2010 E6, and C/2011 W3 (Lovejoy) and infer the ambient solar wind speed. The first comet is located between 3.5 and 6 solar radii (Rs) away from the Sun at high latitudes; the estimated solar wind speed is about 300-500 km s<sup>-1</sup>. The second comet is located within 10 Rs and about 20\textdegree away from the ecliptic; the estimated solar wind speed is about 200-320 km s<sup…
2020


<p>Turbulence, a ubiquitous phenomenon in interplanetary space, is crucial for the energy conversion of space plasma at multiple scales. This work focuses on the propagation, polarization, and wave composition properties of the\&nbsp;solar\&nbsp;wind turbulence within 0.3 au, and its variation with heliocentric distance at magnetohydrodynamic scales (from 10 s to 1000 s in the spacecraft frame). We present the probability density function of propagation wavevectors (PDF (k(parallel to),k)) for\&nbsp;solar\&nbsp;wind turbulence within 0.3 au for the first time: (1) wavevectors cluster quasi-(anti-)parallel to the local background magnetic field forkd(i) \&lt; 0.02, whered(i)is the ion inertial length; (2) wavevectors shift to quasi-perpendicular directions forkd(i) \&gt; 0.02. Based on our wave composition diagnosis, we find that: the outward/anti-sunward Alfven mode dominates over the whole range of scales and distances, the spectral energy density…
2020


<p>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<sub>☉</sub>. 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 mass due to their larger area. By assuming a constant mass flux, and constraints on proton flux measured by Parker Solar Probe (PSP), we estimate an outflow speed within solar minimum…
2020


<p>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<sup>-1</sup> 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 full day earlier before the CME finally gathers enough velocity to propagate outward. This EUV feature appears as a brightness enhancement in cooler temperatures, such as 171 \r A, but as…
2020