Abstract We present an event observed by Parker Solar Probe (PSP) at ∼0.2 au on 2022 March 2 in which imaging and in situ measurements coincide. During this event, PSP passed through structures on ...the flank of a streamer blowout coronal mass ejection (CME) including an isolated flux tube in front of the CME, a turbulent sheath, and the CME itself. Imaging observations and in situ helicity and principal variance signatures consistently show the presence of flux ropes internal to the CME. In both the sheath and the CME interval, the distributions are more isotropic, the spectra are softer, and the abundance ratios of Fe/O and He/H are lower than those in the isolated flux tube, and yet elevated relative to typical plasma and solar energetic particle abundances. These signatures in the sheath and the CME indicate that both flare populations and those from the plasma are accelerated to form the observed energetic particle enhancements. In contrast, the isolated flux tube shows large streaming, hard spectra, and large Fe/O and He/H ratios, indicating flare sources. Energetic particle fluxes are most enhanced within the CME interval from suprathermal through energetic particle energies (∼keV to >10 MeV), indicating particle acceleration, as well as confinement local to the closed magnetic structure. The flux-rope morphology of the CME helps to enable local modulation and trapping of energetic particles, in particular along helicity channels and other plasma boundaries. Thus, the CME acts to build up energetic particle populations, allowing them to be fed into subsequent higher-energy particle acceleration throughout the inner heliosphere where a compression or shock forms on the CME front.
Abstract
In this paper we examine a low-energy solar energetic particle (SEP) event observed by IS⊙IS’s Energetic Particle Instrument-Low (EPI-Lo) inside 0.18 au on 2020 September 30. This small SEP ...event has a very interesting time profile and ion composition. Our results show that the maximum energy and peak in intensity are observed mainly along the open radial magnetic field. The event shows velocity dispersion, and strong particle anisotropies are observed throughout the event, showing that more particles are streaming outward from the Sun. We do not see a shock in the in situ plasma or magnetic field data throughout the event. Heavy ions, such as O and Fe, were detected in addition to protons and 4He, but without significant enhancements in 3He or energetic electrons. Our analysis shows that this event is associated with a slow streamer blowout coronal mass ejection (SBO-CME), and the signatures of this small CME event are consistent with those typical of larger CME events. The time–intensity profile of this event shows that the Parker Solar Probe encountered the western flank of the SBO-CME. The anisotropic and dispersive nature of this event in a shockless local plasma gives indications that these particles are most likely accelerated remotely near the Sun by a weak shock or compression wave ahead of the SBO-CME. This event may represent direct observations of the source of the low-energy SEP seed particle population.
Abstract
On 2020 November 30, Parker Solar Probe (PSP) was crossed by a coronal mass ejection (CME)-driven shock, which we suggest was also crossing a convected, isolated magnetic structure (MS) at ...about the same time. By analyzing PSP/FIELDS magnetic field measurements, we find that the leading edge of the MS coincided with the crossing of the shock, while its trailing edge, identified as a crossing of a current sheet, overtook PSP about 7 minutes later. Prior to the arrival of the shock, the flux of 30 keV–3 MeV ions and electrons, as measured by PSP/Integrated Science Investigation of the Sun (ISOIS)/Energetic Particle Instrument (EPI-Lo), increased gradually, peaking at the time of the shock passage. However, during the crossing of the MS downstream of the shock, the energetic-ion flux dropped dramatically, before recovering at about the time of the crossing of the trailing edge of the MS. Afterwards, the ion fluxes remained approximately constant within the sheath region of the CME shock. We interpret this depletion of energetic ions within the MS as the result of insufficient time to accelerate particles at the shock within the MS, given that the structure moves along the shock surface owing to its advection with the solar wind. We present results from a quantitative numerical model of the interaction of an idealized MS with a shock, which supports this interpretation.
We analyze an energetic proton event associated with a stream interaction region (SIR) that was observed at Parker Solar Probe on day 320 of 2018 when the spacecraft was just 0.34 AU from the Sun. ...Using the Integrated Science Investigation of the Sun instrument suite, we perform a spectral analysis of the event and show how the observed spectra evolve over the course of the event. We find that the spectra from the first day of the event are much more consistent with local acceleration at a weak compression, while spectra from later on are more typical of SIR-related events in which particles accelerated at distant shocks dominate. After the first day, the spectra remain approximately constant, which indicates that the modulation of energetic particles during transit from the presumed source region is weaker than previously thought. We argue that these observations can be explained by a sub-Parker spiral magnetic field structure connecting the spacecraft to a source region in the SIR that is relatively close to the Sun. We further propose that acceleration at weak, pre-shock compressions likely plays an important role in observations of SIR-related events in the inner heliosphere and that future modelling of such events should consider acceleration all along the compression region, not just at the distant shock region.
The New Horizons spacecraft offered a unique opportunity to explore the distant Jovian magnetotail to over 2565 Jovian Radii. Previous observations of ion abundances were available only out to ∼150 ...Jovian Radii. During the 100+‐day exploration of the magnetotail, New Horizons observed a number of energetic particle bursts, similar to particle bursts observed by Galileo much closer to Jupiter. We examine the composition of these dynamic structures and compare the ion abundances with those found in more quiescent regions. We show that the composition of these energetic bursts is Iogenic and suggest it is within these bursts that Jupiter releases the bulk of its energetic material. We report on the ion composition ratios as a function distance down the Jovian magnetotail, finding an increasing intrusion of interplanetary He into the tail with distance from the planet. These observations show that the radial gradients in particle flux observed by Galileo in the magnetotail close to Jupiter extend deep into the magnetotail. We observed large electron intensities at the noon magnetopause crossing and continuous strong 10‐h modulations in electron intensity to nearly 500 Jovian Radii toward the tail. Our current hypothesis is that Jupiter enforces azimuthal rotation on some fields to distances of over a few hundred Jovian Radii. At distances greater than 500 Jovian Radii we observed long‐duration periods of strong electron anisotropy beaming down the magnetotail. Intermittent observations of 10‐h electron modulations continue into distant regions of the magnetotail and we suggest these are a signature of occasional field line connection to the magnetosphere.
Abstract
Energetic electrons of Jovian origin have been observed for decades throughout the heliosphere, as far as 11 au, and as close as 0.5 au, from the Sun. The treatment of Jupiter as a ...continuously emitting point source of energetic electrons has made Jovian electrons a valuable tool in the study of energetic electron transport within the heliosphere. We present observations of Jovian electrons measured by the EPI-Hi instrument in the Integrated Science Investigation of the Sun instrument suite on Parker Solar Probe at distances within 0.5 au of the Sun. These are the closest measurements of Jovian electrons to the Sun, providing a new opportunity to study the propagation and transport of energetic electrons to the inner heliosphere. We also find periods of nominal connection between the spacecraft and Jupiter in which expected Jovian electron enhancements are absent. Several explanations for these absent events are explored, including stream interaction regions between Jupiter and Parker Solar Probe and the spacecraft lying on the opposite side of the heliospheric current sheet from Jupiter, both of which could impede the flow of the electrons. These observations provide an opportunity to gain a greater insight into electron transport through a previously unexplored region of the inner heliosphere.
Suprathermal Ions in the Outer Heliosphere Kollmann, Peter; Hill, M. E.; McNutt, R. L. ...
Astrophysical journal/The Astrophysical journal,
05/2019, Letnik:
876, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Suprathermal ions form from interstellar gas that is first ionized into pickup ions and then accelerated to tens and hundreds of keV in energy. The resulting suprathermal ion spectra with hundreds of ...keV have been previously observed throughout the heliosphere; however, measurements at lower energies, around the pickup ion cutoff energy where they are accelerated from, were limited to <10 au. Here we present a statistical study of suprathermal ions in the keV to hundred keV energy range. We use the Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI) instrument on the New Horizons spacecraft, which recorded observations at a wide range of heliocentric distances, and compare these measurements to charge energy mass spectrometer (CHEMS) observations on Cassini, which cruised to and remained at Saturn. We find that the power-law exponents of suprathermal ion intensity over energy are between −1 and −2, change abruptly close to discontinuities that are likely corotating merged interaction regions, correlate with the solar wind bulk speed, and show a long-term evolution on the timescale of the solar cycle. The independent measurements from New Horizons and Cassini are consistent, confirming the first fully calibrated measurements from the New Horizons/PEPSSI instrument.
We present a time‐of‐flight mass spectrometer design for the measurement of ions in the ~30 keV to 10 MeV range for protons (up to ~40 MeV and ~150 MeV for He and heavy ions, respectively) and ~30 ...keV to 1 MeV range for electrons, covering half of the sky with 80 apertures. The instrument, known as the “Mushroom,” owing to its shape, solves the field of view problem for magnetospheric and heliospheric missions that employ three‐axis stabilized spacecraft, yet still require extended angular coverage; the Mushroom is also compatible with a spinning spacecraft. The most important new feature of the Mushroom is the method through which uncomplicated electrostatic optics and clean position sensing combine to permit many apertures to fit into a compact, low‐mass sensor head (or wedge), several of which (ideally eight) compose a full instrument. Most of the sensor head's volume is an empty, equipotential region, resulting in the modest 250 g mass of each 10‐aperture wedge. The Mushroom is capable of separating ion species across most of its energy range and angular field of view. For example, separation of the neighboring 3He and 4He isotopes is excellent; the full width at half maximum mass resolution has been measured to be 0.24 amu to 0.32 amu, respectively. Converting this to a Gaussian width σm in mass m, this represents a σm/m mass resolution better than 0.04. This separation is highly desirable for the flight program for which the first Mushroom was built, the Solar Probe Plus mission. More generally, we estimate the mass resolution to be σm/m ≈ 0.1, but this is energy, mass, and angularly dependent. We also discuss the solid‐state detector stack capability, which extends the energy range of protons and helium, with composition, to ~100 MeV.
Key Points
Anisotropy, pitch angle distributions, and large field of view are important for energetic ion and electron science
The “Mushroom” instrument has been developed by JHU/APL to provide needed large FOV and angular resolution
The first Mushroom, EPI‐Lo, part of the ISʘIS investigation on Solar Probe Plus, has achieved excellent composition and spatial separation
Abstract
We present observations of ≳10–100 keV nucleon
−1
suprathermal (ST) H, He, O, and Fe ions associated with crossings of the heliospheric current sheet (HCS) at radial distances of <0.1 au ...from the Sun. Our key findings are as follows: (1) very few heavy ions are detected during the first full crossing, the heavy-ion intensities are reduced during the second partial crossing and peak just after the second crossing; (2) ion arrival times exhibit no velocity dispersion; (3) He pitch-angle distributions track the magnetic field polarity reversal and show up to ∼10:1 anti-sunward, field-aligned flows and beams closer to the HCS that become nearly isotropic farther from the HCS; (4) the He spectrum steepens either side of the HCS, and the He, O, and Fe spectra exhibit power laws of the form ∼
E
−4
–
E
6
; and (5) maximum energies
E
X
increase with the ion’s charge-to-mass (
Q
/
M
) ratio as
E
X
/
E
H
∝
(
Q
X
/
M
X
)
δ
, where
δ
∼ 0.65–0.76, assuming that the average
Q
states are similar to those measured in gradual and impulsive solar energetic particle events at 1 au. The absence of velocity dispersion in combination with strong field-aligned anisotropies closer to the HCS appears to rule out solar flares and near-Sun coronal-mass-ejection-driven shocks. These new observations present challenges not only for mechanisms that employ direct parallel electric fields and organize maximum energies according to
E
/
Q
but also for local diffusive and magnetic-reconnection-driven acceleration models. Reevaluation of our current understanding of the production and transport of energetic ions is necessary to understand this near-solar, current-sheet-associated population of ST ions.
Characterizing Europa’s subsurface ocean is essential for assessing Europa’s habitability. The suite of instruments on the Europa Clipper spacecraft will, among others, magnetically sound Europa’s ...interior by measuring the ocean’s induced magnetic field. This magnetic field is generated in response to the Jovian time-varying magnetic environment in which Europa is immersed. However, the dynamic magnetized plasma flow of the Jovian magnetosphere creates electrical currents that give rise to magnetic perturbations near Europa. These perturbations complicate the interpretation of the induction signal, and hence the characterization and inferences on potential habitability. Thus, characterization of the ocean by magnetic sounding requires an accurate characterization of the plasma as it flows across Europa.
We present the Plasma Instrument for Magnetic Sounding (PIMS), the instrument for the Europa Clipper mission that will measure the plasma contribution to the magnetic field perturbations sensed by the Europa Clipper Magnetometer. PIMS is composed of four Faraday Cup plasma spectrometers that use voltage-biased gridded apertures to dissect the space plasmas that they encounter. The instrument uses sensitive preamplifiers and processing electronics to measure the current that results when charged particles strike the instrument’s metal collector plates, thus enabling a measure of the plasma characteristics near Europa to produce a more accurate magnetic sounding of Europa’s subsurface ocean. PIMS consists of two sensors: one placed near the top of the Europa Clipper spacecraft and one near the bottom. Each sensor contains two Faraday Cups with a 90° full-width field-of-view. The sensors were specifically designed to withstand the Europa environment, measure both ions and electrons, and have two separate voltage ranges intended to analyze the magnetospheric and ionospheric environments, respectively. In this paper, we describe the scientific motivation for this experiment, the design considerations for the PIMS instrument, the details of the ground calibration, and other details pertinent to understanding the scientific data retrieved by PIMS.
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