G. Stenborg’s research while affiliated with Johns Hopkins Medicine and other places

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Publications (179)


Figure 8. Diagram of 3D stationary point geometry. Everything is in the x − y plane except for the parcel, its velocity, and the angles α and θ. The in-plane geometry is that of Figure 1, though the parcel location in that case has become here the in-plane projection of the parcel.
The Stationary Point: A New Method for Solar Wind Speed Measurements from a Moving Vantage Point
  • Preprint
  • File available

February 2025

Samuel J. Van Kooten

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Craig E. Deforest

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Guillermo Stenborg

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Kenny N. Kenny

The WISPR imager on Parker Solar Probe provides a unique view the young solar wind, flying through solar wind structures at high speed. It is of interest to use WISPR image sequences to measure the velocity of both large features (such as CMEs) and the background, ambient wind. However, WISPR's close-up, rapidly-moving perspective makes the usual methods for measuring velocities from images difficult or impossible to apply, as most apparent motion through the image is due to the motion or rotation of the imager. In this work, we propose a new method of looking for features at the "stationary point" -- a direction from which some plasma parcels appear to approach the spacecraft, remaining at a constant direction in the image sequence. This direction is a function of the plasma's radial velocity, the encounter geometry, and the spacecraft velocity, allowing the former two to be inferred. We demonstrate the technique with forward-modeled images, and we apply it to WISPR observations, inferring the speed and trajectory of a particular density feature. This method promises to enable speed measurements of the young solar wind in an important acceleration region, from a close-up perspective and at latitudes well outside the PSP orbital plane. And while we present this method in a solar wind context, it is broadly applicable to any situation of a moving viewpoint traveling through an expanding cloud of features.

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A Study on the Nested Rings CME Structure Observed by the WISPR Imager Onboard Parker Solar Probe

November 2024

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9 Reads

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1 Citation

The Astrophysical Journal

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Mark G. Linton

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Sarah E. Gibson

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[...]

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Despite the significance of coronal mass ejections (CMEs) in space weather, a comprehensive understanding of their interior morphology remains a scientific challenge, particularly with the advent of many state-of-the-art solar missions such as Parker Solar Probe (Parker) and Solar Orbiter (SO). In this study, we present an analysis of a complex CME as observed by the Wide-Field Imager for Solar PRobe (WISPR) heliospheric imager during Parker’s seventh solar encounter. The CME morphology does not fully conform with the general three-part density structure, exhibiting a front and core not significantly bright, with a highly structured overall configuration. In particular, its morphology reveals nonconcentric nested rings, which we argue are a signature of the embedded helical magnetic flux rope of the CME. For that, we analyze the morphological and kinematical properties of the nested density structures and demonstrate that they outline the projection of the three-dimensional structure of the flux rope as it crosses the lines of sight of the WISPR imager, thereby revealing the magnetic field geometry. Comparison of observations from various viewpoints suggests that the CME substructures can be discerned owing to the ideal viewing perspective, close proximity, and spatial resolution of the observing instrument.


A Study on the Nested Rings CME Structure Observed by the WISPR Imager Onboard Parker Solar Probe

October 2024

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19 Reads

Despite the significance of coronal mass ejections (CMEs) in space weather, a comprehensive understanding of their interior morphology remains a scientific challenge, particularly with the advent of many state-of-the-art solar missions such as Parker Solar Probe (Parker) and Solar Orbiter (SO). In this study, we present an analysis of a complex CME as observed by the Wide-Field Imager for Solar PRobe (WISPR) heliospheric imager during Parker's seventh solar encounter. The CME morphology does not fully conform with the general three-part density structure, exhibiting a front and core not significantly bright, with a highly structured overall configuration. In particular, its morphology reveals non-concentric nested rings, which we argue are a signature of the embedded helical magnetic flux rope (MFR) of the CME. For that, we analyze the morphological and kinematical properties of the nested density structures and demonstrate that they outline the projection of the three-dimensional structure of the flux rope as it crosses the lines of sight of the WISPR imager, thereby revealing the magnetic field geometry. Comparison of observations from various viewpoints suggests that the CME substructures can be discerned owing to the ideal viewing perspective, close proximity, and spatial resolution of the observing instrument.



Figure 1. Evolution of the SA in E15 for a LOS at 77° . 7 elongation in WISPR-O images compared to the projections of the orbits of Jupiter (JOP) and Venus (VOP) as a function of (1) time (top left panel), (2) S/C longitude (top right panel), (3) S/C heliocentric distance (bottom left panel), and (4) S/C latitude in the HAE system (bottom right panel). The dashed, black vertical line points out the perihelion, and the dashed, green vertical line the moment when the S/C is at its maximum elevation over the ecliptic. The dashed, pink lines in the bottom right panel connect locations in the inbound and outbound segment at equal heliocentric distances (0.25, 0.15, 0.11, 0.085, and 0.068 au).
Figure 2. Elevation of various features in the HPC system as a function of S/C helioecliptic latitude (HAE) for nine selected LOSs in WISPR-O. The four features are the SA inbound (in blue), SA outbound (in light blue), and the projections of the Jupiter and Venus orbits (JOP in red and VOP in green, respectively). The orange line delineates a fifth-degree polynomial fit to the measurements of the location of the SA at the corresponding LOS. The black line at 0° elevation delineates the projection of the solar equator. The dashed pink lines in the bottom right panel connect locations in the inbound and outbound segments at equal heliocentric distances (namely, at [0.25, 0.15, 0.11, 0.085, 0.068] au). The encounters start at the lower left and proceed counterclockwise around the plots.
Figure 4. Left panel: normalized median brightness per encounter and segment in selected elongation distance ranges (as specified in the inset labels). The colored circles (diamonds) depict the median brightness values in the inbound (outbound) segment of the PSP encounters. The brightness trend in the different elongation distances ranges, for the inbound and outbound segments, are delineated with the colored solid and dashed lines, respectively. Right panel: normalized median brightness in the 30−105 R ☉ elongation distance range in the outbound segment of each PSP encounter (black dots, with the scale on the left axis) and latitudinal angular separation between the SSB and Jupiter (red dots, with the scale on the right axis). The values in both panels are displayed as a function of Jupiter's average longitude (in the HAE system) during each encounter. The yellow, shaded area points the eye to the region where the decreasing trend is observed. For details see the text.
Figure 5. Left panel: trajectory of the SSB (blue dots) in E10-E16. The continuous black line delineates the SSB trajectory since the beginning of the PSP to the present day. The dashed (dashed-dotted) lines point out the average direction of Jupiter (Saturn) during the encounters. Right panel: the WISPR-O FOV during the inbound (pink shaded area) and outbound (violet shaded area) segments of E10-E16. The orbit of PSP is shown in orange, with the portion in brown (blue) indicating the inbound (outbound) segment of the encounters. The orbits of the five innermost planets are shown with the gray, dashed lines (Jupiter orbit not to scale). The orbits of Venus and Jupiter are both delineated with the red/blue dots, the color code indicating whether they are above/below the ecliptic plane (the intensity represents the elevation above the ecliptic). The coordinates of the PSP ([r, longitude, latitude] in the HAE system) at the time of E13 perihelion are given in the upper left corner.
Figure 7. Elevation of various features in the HPC system as a function of the S/C's heliocentric distance for the same nine LOSs in WISPR-O selected for Figure 2. The four features are the SA inbound (in blue), SA outbound (in light blue), and the projections of Jupiter and Venus orbits (JOP, in red; and VOP in green, respectively). The orange line delineates the fifth-degree polynomial fit to the measurements of the location of the SA at the corresponding LOS. The black line at 0° elevation delineates the projection of the solar equator. The black dot marks the moment when the S/C is at its maximum latitude, and the dashed line points out the heliocentric distance of the S/C at that moment (0.0636 au). The beginning of the encounters start in the lower right and proceeds clockwise around the plots.
Novel Insights on the Dust Distribution in the Zodiacal Dust Cloud from PSP/WISPR Observations at Large Elongations

August 2024

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33 Reads

The Astrophysical Journal

The Wide-Field Imager for Solar Probe (WISPR) on the Parker Solar Probe (PSP) mission maps the brightness produced by the zodiacal dust cloud (ZDC) from an historically unprecedented viewpoint. The brightness results from the scattering of photospheric light by dust particles in the ZDC, and is called zodiacal light (ZL). We exploit the PSP nominal science encounters in orbits 10 through 16 for an in-depth study of the location and brightness evolution of the symmetry axis of the ZL in images taken with the WISPR outer telescope (WISPR-O). During these 11 day encounters, PSP covered heliocentric distances between 0.25 and 0.0617 au (∼53.78−13.28 R ☉ ) and ∼255° in helioecliptic longitude from within the orbital plane of Venus. The unique WISPR-O viewpoint, which comprises line-of-sight elongations of 80° ± 27°, has led to further insights about the ZDC. Namely, we find that the gravitational pull of the planets warps the ZDC symmetry plane and shifts the ZDC towards the solar system barycenter, creating an east–west asymmetry in the ZL brightness. Additionally, our analysis provides the first consistent observational evidence of a circumsolar dust enhancement resulting from the sublimation of dust grains at ∼25 R ☉ . Overall, the WISPR observations from the PSP platform are opening a new window in the remote sensing of the ZDC.


Evidence of Continuous Reconnection along a Helmet Streamer Current Sheet Observed by WISPR on Parker Solar Probe

July 2024

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18 Reads

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4 Citations

The Astrophysical Journal

Parker Solar Probe's second solar encounter from 2019 March 30 to April 11 occurred during a period when the corona had a simple magnetic structure and relatively flat heliospheric current sheet (HCS), which was in the field of view of the Wide-field Imager for Solar Probe (WISPR) throughout. The images show an almost continual flow of transient density enhancements ( streamer blobs ) of various sizes near the latitude of the HCS during the entire 11 day encounter period. The high resolution and sensitivity of WISPR reveal the structure of some of the individual blobs not seen in observations from 1 au. Many of the blobs show dark central cores, suggesting that they are magnetic flux ropes. The 3D trajectories and sizes of four representative streamer blobs have been determined using the tracking and fitting technique of Liewer et al. (2020). Comparison of the location of these blobs with synoptic white-light maps for this time period, created using data from the Large Angle and Spectrometric Coronagraph (Brueckner et al. 1995) on board the Solar and Heliospheric Observatory, confirms that the blobs are at the location of the helmet streamer associated with the HCS. The blobs were observed in the region beyond 15 R ☉ . The continual flow of blobs, the confirmation of their location at the HCS, and their flux-rope-like appearance provide strong evidence that the process of reconnection across the current sheet dominates the slow wind near the HCS.


Internal magnetic field structures observed by PSP/WISPR in a filament-related coronal mass ejection

May 2024

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44 Reads

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3 Citations

Astronomy and Astrophysics

Context. We investigated the coronal mass ejection (CME) related to an eruptive filament over the southwestern solar limb on December 8, 2022, at around 8 UT. We tracked localized density enhancements reflecting the magnetic structures using white-light data taken with the Wide-field Instrument for Solar PRobe (WISPR) aboard the Parker Solar Probe (PSP). Aims. We aim to investigate the 3D location, morphology and evolution of the internal magnetic fine structures of CMEs. Specifically, we focused on the physical origin of the features in the WISPR images, how the white-light structures evolve over time, and their relationship with the source region, filament, and the flux rope. Methods. The fast tangential motion of the PSP spacecraft during its perihelion permits a single event to be viewed from multiple angles in short times relative to the event’s evolution. Hence, three-dimensional information of selected CME features can be derived from this single spacecraft using triangulation techniques. Results. We grouped small-scale structures with roughly similar speeds, longitude, and latitude into three distinct morphological groups. We found twisted magnetic field patterns close to the eastern leg of the CME that may be related to “horns” outlining the edges of the flux-rope cavity. We identified aligned thread-like bundles close to the western leg, and they may be related to confined density enhancements evolving during the filament eruption. High density blob-like features (magnetic islands) are widely spread in longitude (∼40°) close to the flanks and the rear part of the CME. We also note that the large-scale outer envelope of the CME, seen clearly from 1 AU, was not well observed by PSP. Conclusions. We demonstrate that CME flux ropes, apart from the blobs, may comprise different morphological groups with a cluster behavior; the blobs instead span a wide range of longitudes. This finding may hint at either the three-dimensionality of the post-CME current sheet (CS) or the influence of the ambient corona in the evolutionary behavior of the CS. Importantly, we show that the global appearance of the CME can be very different in WISPR (0.11–0.16 AU) and the instruments near 1 AU because of the shorter line-of-sight integration of WISPR.


A Coronal Mass Ejection Impacting Parker Solar Probe at 14 Solar Radii

April 2024

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77 Reads

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4 Citations

The Astrophysical Journal

The relationship between CME properties in the corona and their interplanetary counterparts is not well understood. Until recently, a wide spatial gap existed between the two regions, which prevented us from disentangling the spatial and temporal evolution of CMEs. NASA’s Parker Solar Probe (PSP) has imaged multiple CMEs since its launch in 2018, but these events either intercepted the spacecraft far from the corona or completely missed it. Here we describe one of the first CMEs observed simultaneously by remote sensing and in situ instruments, and compare the corresponding measured properties, such as orientation, cross section diameter, density, and speed. The CME encounter occurred on 2022 June 2, while PSP was around 14 solar radii from the Sun center. We reconstruct the CME with forward modeling and determine its morphology and kinematics. The reconstruction suggests that PSP misses the CME apex but encounters its flank. The encounter time matches the period when the PSP in situ measurements indicate the passage of a CME. We also reconstruct the flux rope diameter and orientation using the in situ magnetic field measurements. The results are consistent with the CME reconstruction from imaging data. The close agreement between remote sensing and in situ analyses suggests that discrepancies found in past studies are more likely associated with the CME temporal evolution. We also find that the magnetic field of the CME flank extrapolated to 1 au is well below the average solar wind background and likely indistinguishable from it. This point could explain past events where the CMEs' interplanetary counterparts were not identified.


Figure 2. PSP position (red star) on 2021 November 20 at 02:30 UT in the Heliocentric Earth Ecliptic (HEE) coordinate system. The CME angular width (dashed blue lines) and direction of propagation (solid blue line), as defined by the GCS reconstruction, are also indicated. The direction of ST-A (Earth) is indicated with the solid magenta (green) line. The PSP orbit is depicted with the orange line and its perihelion is represented with the orange diamond. The FOV of WISPR-I is represented by the light gray-shaded region bordered with solid red lines. The projection of the Thomson surface is delineated with a gray circle.
Figure 5. Determination of the eddy centroids. Left panel: excess brightness profile (black dots) along a slit covering the train of eddies on the WISPR-I image taken on 2021 November 20 at 02:18 UT. The blue curve depicts the low-pass filtered profile used for the determination of the relative maxima. The magenta dots point out the relative maxima, which are representative of the position of the centroids of the eddies. Right panel: estimated centroid locations (magenta dots) on the corresponding cropped WISPR-I image.
Figure 7. CME magnetic field constraints for the development of KHI (Equation (6)). Top panel: assuming a scaling factor d in the Leblanc density model (Equation (7)) as in Thernisien & Howard (2006; i.e., d = 6.0). Lower panel: assuming d ≈ 0.5 to match the in situ PSP/SWEAP (Kasper et al. 2016) density measurements when PSP crossed the leg of the CME (S/C at ∼14.1 R ☉ , between November 20 23:00 UT and November 21 01:00 UT). The colored, continuous lines delineate Equation (6) when both sides are equal for x = = 1, 2 n
Figure 9. Top panel: Alfvén speed, V A , on a Carrington projection (rotation 2251) from the MAS model at 8.43 R e . The propagation direction of the CME on 2021 November 20 at 02:00 UT is pointed out with the magenta star symbol (i.e., about the time the eddies were observed). This direction is very close to the heliospheric current sheet (delineated with the white line). The local Alfvén speeds in this area are very low (of the order of 30 km s −1 ). Lower panel: V A radial profiles from the MAS model for the Carrington longitude and latitude of the CME considering a 2° (in light blue) and a 5° (in gray) error. The red line represents the radial profile considering the CME direction of propagation, and the dashed green line represents the limit condition V A = 1 3
First Direct Imaging of a Kelvin–Helmholtz Instability by PSP/WISPR

March 2024

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86 Reads

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1 Citation

The Astrophysical Journal

We present a comprehensive analysis aimed at proving the hypothesis that a train of small-scale features observed by the Wide-field Imager (WISPR) onboard the Parker Solar Probe (PSP) are the signature of a Kelvin–Helmholtz instability (KHI). These features were seen near the flank of a Coronal Mass Ejection (CME) wake between 7.5 R ⊙ and 9.5 R ⊙ , lasting for about 30 minutes. The CME was a slow event, associated with a streamer blowout. We analyzed the size of the eddies and found growth during their evolution while maintaining separation distances and alignment typical of Kelvin–Helmholtz vortexes. We then assessed the magnetic field conditions that would make the observation of such an instability plausible. Two methods were used to cross-check our findings. The measured thickness of the boundary layer supports KHI candidacy, and the estimated linear growth rate suggests nonlinear saturation within the expected timescale. We conclude that a KHI is a plausible explanation for the observed features, and therefore that such instabilities might exist in the low and middle solar corona (within ∼15 R ⊙ ) and can be detected in white light observations. Their observation, however, might be rare due to stringent conditions like the observer’s proximity, suitable viewing circumstances, magnetic field topology, and flow properties. This study highlights the unique capability of PSP/WISPR in observing such phenomena, especially as PSP perihelia reach closer distances to the Sun.


The evolution of our understanding of coronal mass ejections

November 2023

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134 Reads

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5 Citations

Frontiers in Astronomy and Space Sciences

The unexpected observation of a sudden expulsion of mass through the solar corona in 1971 opened up a new field of interest in solar and stellar physics. The discovery came from a white-light coronagraph, which creates an artificial eclipse of the Sun, enabling the viewing of the faint glow from the corona. This observation was followed by many more observations and new missions. In the five decades since that discovery, there have been five generations of coronagraphs, each with improved performance, enabling continued understanding of the phenomena, which became known as Coronal Mass Ejection (CME) events. The conceptualization of the CME structure evolved from the elementary 2-dimensional loop to basically two fundamental types: a 3-dimensional magnetic flux rope and a non-magnetic eruption from pseudo-streamers. The former persists to 1 AU and beyond, whereas the latter dissipates by 15 R ⊙ . Historically, most of the studies have been devoted to understanding the CME large-scale structure and its associations, but this is changing. With the advent of the fourth and fifth coronagraph generations, more attention is being devoted to the their internal structure and initiation mechanisms. In this review, we describe the evolution of CME observations and their associations with other solar and heliospheric phenomena, with one of the more important correlations being its recognition as a driver of space-weather. We conclude with a brief overview of open questions and present some ideas for future observations.


Citations (68)


... For example, Howard et al. (2022) investigated the evolution and dissolution of the CME leading edge into multiple fronts and a fair amount of overlapping internal substructure in the CME "core" region. Shaik et al. (2024) have examined the nested-ring WL structures of CMEs, showing they were consistent with concentric flux surfaces. The distortion of the WL CME cavity shape (flux rope cross-section) during its interaction with the structured background wind was investigated by Braga et al. (2022). ...

Reference:

Synthetic Remote-sensing and In-situ Observations of Fine-scale Structure in a Pseudostreamer Coronal Mass Ejection through the Solar Corona
A Study on the Nested Rings CME Structure Observed by the WISPR Imager Onboard Parker Solar Probe

The Astrophysical Journal

... We note, these examples complement and expand an entirely different set of WISPR observations of smaller-scale, slow wind streamer blob and heliospheric current sheet/plasma sheet transient outflow structures (e.g. Rouillard et al. 2020;Réville et al. 2022;Poirier et al. 2020Poirier et al. , 2023Ascione et al. 2024;Liewer et al. 2024). Wyper et al. (2024), hereafter Paper I, performed a detailed magnetohydrodynamic (MHD) simulation with the Adaptively Refined MHD Solver (ARMS; DeVore & Antiochos 2008) of the energization and eruption of a pseudostreamer CME with a particular emphasis on magnetic reconnection and its impact on the CME's dynamic structure and connectivity during different phases of the eruption. ...

Evidence of Continuous Reconnection along a Helmet Streamer Current Sheet Observed by WISPR on Parker Solar Probe

The Astrophysical Journal

... The distortion of the WL CME cavity shape (flux rope cross-section) during its interaction with the structured background wind was investigated by Braga et al. (2022). And recently, Cappello et al. (2024) have examined Large Angle Spectroscopic Coronagraph (LASCO; Brueckner et al. 1995) observations taken by the Solar and Heliospheric Observatory (SOHO; Domingo et al. 1995) in conjunction with simultaneous PSP/WISPR imaging of a CME event that exhibits both complex internal structure and an entire train of highly structured, intermittent post-CME outflows. We note, these examples complement and expand an entirely different set of WISPR observations of smaller-scale, slow wind streamer blob and heliospheric current sheet/plasma sheet transient outflow structures (e.g. ...

Internal magnetic field structures observed by PSP/WISPR in a filament-related coronal mass ejection

Astronomy and Astrophysics

... The CME was observed by remote-sensing instruments (C. R. Braga et al. 2024). It is associated with a filament eruption originating from an AR (named NOAA 13029 later) located at the heliographic coordinate S17E100 from the Earth perspective. ...

A Coronal Mass Ejection Impacting Parker Solar Probe at 14 Solar Radii

The Astrophysical Journal

... Since both σ c and σ r are interdependent with the alignment angles, such effects could potentially influence the SDDA scalings. While it is not possible to rule out such effects, especially given recent in-situ observations (Paouris et al. 2024), it's essential to note that, as demonstrated in Section 5.3, high-frequency instrumental noise in velocity field measurements can contaminate the power spectrum of the ingoing Elsässer field even at lower frequencies. This contamination becomes progressively more significant as the Elsässër imbalance increases, see 8b. ...

First Direct Imaging of a Kelvin–Helmholtz Instability by PSP/WISPR

The Astrophysical Journal

... The results of these measurements make it possible to establish the sequence of phenomena and identify causal relationships. These will help to understand the CME development that still remains unclear (e.g., Howard, Vourlidas, and Stenborg 2023). Finally, an important problem is to identify the contributions of flare processes and shock waves to the acceleration of solar protons reaching the Earth orbit. ...

The evolution of our understanding of coronal mass ejections

Frontiers in Astronomy and Space Sciences

... Two CMEs are observed during the ≈ 7 hour period shown. The bottom row shows data of the same events from the SECCHI payload on STEREO-A (Hess et al. 2023). These plots combine data of SECCHI's coronagraph and heliospheric imager instrument to cover the distance from 6-50 solar radii Perri et al. (2024) observed was small and slow with expansion velocity reaching less than 140 km/s. ...

SoloHI observations of coronal mass ejections observed by multiple spacecraft

Astronomy and Astrophysics

... R ☉ ). The unique set of observations obtained during the nominal science encounters E10-E16 (i.e., when PSP is within 0.25 au from the Sun's center) is being used to develop robust and consistent background brightness models of the ZL for use in the coronal analysis of the WISPR images (e.g., Stenborg et al. 2023). In the process, we uncovered some intriguing trends (the topic of this paper) that together provide a new paradigm for ZL studies in the optical regime. ...

Investigating Coronal Holes and CMEs as Sources of Brightness Depletion Detected in PSP/WISPR Images

The Astrophysical Journal

... The Metis coronagraph boarded on the Solar Orbiter (SO) demonstrates the formation and the thermal structure of such a CS in the near-sun region 19,25 . WISPER also shows that the streamer belt usually comprises multiple narrow rays 26,27 , similar to the rays connecting an eruptive magnetic flux rope (MFR) and underlying flare arcades observed in Atmospheric Imaging Assembly channels 28 . ...

Structure of the Plasma near the Heliospheric Current Sheet as Seen by WISPR/Parker Solar Probe from inside the Streamer Belt

The Astrophysical Journal

... The advent of near Sun in-situ data, starting with PSP's first perihelion in 2018, has provided key insights into the energy source driving the solar wind and how it may be traced to the lower atmosphere. As Raouafi et al. (2023) states, PSP has revealed the highly Alfvénic character of the near Sun solar wind, pointing to a magnetic origin at the Sun, which these authors argue may find its roots in the small-scale reconnection of opposite-polarity flux that forms so-called jetlets. Moreover, this small-scale activity could be linked to the observed magnetic switchbacks in the near Sun solar wind Kasper et al. 2019). ...

Magnetic Reconnection as the Driver of the Solar Wind

The Astrophysical Journal