arXiv subjects

Phillip Hess

Publications and source records attributed to Phillip Hess.

At least 19 recordsLinked to original sources

arXiv2026

Energy Evolution from the Chromosphere to the Heliosphere in the 2021 October 28 Solar Eruption

We perform a detailed study of the energetics for a well-observed solar eruption and flare that occurred on 28 October 2021. This event included a GOES class X1.0 flare, a global EUV wave, and a coronal mass ejection that reached speeds of >2000 km/s. The event was observed from a variety of spacecraft in NASA's Heliophysics System Observatory, including multiple missions near Earth, STEREO-A off the Sun-Earth line, and Solar Orbiter, near the Sun-Earth line at about 0.8 au. Using remote sensing, in situ observations, and in some cases scaling laws based on previous observations, we characterize the following quantities: free magnetic energy, energy in non-thermal electrons, energy in non-thermal ions, bolometric energy, energy deposited in the chromosphere, thermal energy radiated in the flare loops, energy dissipated by the EUV wave, CME kinetic and gravitational potential energy, CME energy flux in the heliosphere, and the energy partition in the CME shock. We find that the total energy released during the event is consistent with estimates of the pre-event stored magnetic energy, and the CME kinetic + potential energy dominates the energy partition.

astro-ph.SR↗

arXiv2026

Polarimetric Tomography Applied to Synthetic Multi-Spacecraft White-Light Images: Observing Coronal Mass Ejections in 3D

A discrete tomography method has been developed that is able to reconstruct three-dimensional coronal mass ejection (CME) density structure. We test the method by producing synthetic coronagraph imagery for three events using the CORona--HELiosphere (CORHEL) model. We combine images from different numbers of observing spacecraft and we perform the method separately using polarimetric and non-polarimetric reconstructions, as a means to test their relative effectiveness. We show that increasing the number of observing spacecraft consistently reduces the mean relative absolute error (MRAE) between the simulated and reconstructed density. Furthermore, the MRAE is generally lower when using polarimetric reconstructions compared to non-polarimetric reconstructions. Methods applied to localise the CME front work well for all spacecraft configurations, and are improved when using polarimetric, over non-polarimetric, reconstructions. The presence of a CME front can be identified with an accuracy of $(72\pm9)\%$, $(70\pm8)\%$ and $(52\pm12)\%$ for CME1, CME2 and CME3 via polarimetric reconstructions using only three spacecraft at L1, L4 and L5. The radial position of the CME front can be constrained to a high level of precision when using polarimetric reconstructions using the same three spacecraft; $0.003\pm0.004$\,au, $0.004\pm0.005$\,au and $0.005\pm0.004$\,au for CME1, CME2 and CME3, respectively. We expect that at least four spacecraft are required in order to derive accurate information about 3D CME structure. We find no strong evidence of improvement when including out-of-ecliptic observers, but that their inclusion increases the volume of space within which the inversion can be performed.

astro-ph.SR↗

arXiv2026

The First Quantitative Study of Tail Regrowth of CME-Driven Disconnection in Comet C/2023 P1 Nishimura

Comet C/2023 P1 (Nishimura) was observed by the Solar Orbiter Heliospheric Imager (SoloHI), onboard the Solar Orbiter spacecraft, from 2023 September 1 to 14. During this period, the ion tail of the comet exhibited continual fluctuations and four tail disconnection events (TDEs), each coinciding with the passage of a coronal mass ejection (CME). In this work, we report on the ion tail dynamics of the best observed TDE, which occurred on September 11. The SoloHI white-light images reveal an abrupt bending, subsequent kinks, and severing of a downstream portion of the pre-existing ion tail. The onset of disconnection occurred $\sim$6.5 hours after the projected passage of the CME leading edge in the images, consistent with a CME flank encounter. After the disconnection, the ion tail reformed within $\sim$24 hours, with a regrowth rate of $\sim$86$\pm7~\mathrm{km\,s^{-1}}$, indicating the rate at which newly ionized material forms along the magnetic field draped around the comet's coma. After the TDE, the detached tail drifted anti-sunward at an estimated speed of $\sim$295$\pm20~\mathrm{km\,s^{-1}}$, comparable to the local CME flank's speed, suggesting that the severed plasma was most likely carried away from the comet by the CME. This study provides the first direct, quantitative characterization of comet-CME interactions and the subsequent regrowth phase of a cometary TDE. These measurements were achievable by SoloHI's unique inner-heliospheric coverage, thanks to a combination of high photometric sensitivity, short exposure times, and a wide field of view that preserves the fine-scale tail dynamics.

astro-ph.SR↗

arXiv2025

Understanding the complex morphology of a CME: multi-view analysis and numerical modeling

Although all coronal mass ejections (CMEs) that propagate into the heliosphere should contain a magnetic flux rope (MFR) component, the majority do not exhibit the expected white-light MFR morphology of a leading edge plus cavity. This different appearance could be the result of distortion of the internal magnetic structure, merging with other structures, or simply projection effects. These factors complicate the interpretation of CMEs. This complexity is exemplified by a CME observed on 28 March 2022. The event originated from a single eruption, evolving as a textbook CME in the low corona but appearing as a complex two-MFR structure in white-light observations. Why? To answer this question, we performed a multi-view data and modeling analysis to describe the CME coronal evolution. The thermodynamic MHD model, CORHEL-CME, helps reveal the magnetic configuration of this CME and also reveals that the ambient field plays a crucial role in shaping the complex structure of the CME during early evolution. Our research underscores the importance of integrating multiview observations with physics-based models to gain a deeper insight into the development of complex CMEs.

astro-ph.SR↗

arXiv2025

Testing the Flux Rope Paradigm for Coronal Mass Ejections Using a Three Spacecraft Encounter Event

We present a 3-D morphological and field reconstruction of a coronal mass ejection (CME) from 2023 November 28, which hits three spacecraft near 1 au: Wind at Earth's L1 Lagrange point; STEREO-A with a longitudinal separation of $6.5^{\circ}$ west of Earth; and Solar Orbiter (SolO) at $10.7^{\circ}$ east of Earth. The reconstruction assumes a magnetic flux rope (MFR) structure for the CME. With this event, we test whether field tracings observed by a spacecraft passing near the central axis of a CME MFR (STEREO-A) can be used to successfullly predict the field behavior seen by a spacecraft $17^{\circ}$ away (SolO), which has a more grazing encounter with the CME. We find that the MFR model does have significant success in simultaneously reproducing the field signs and rotations seen at STEREO-A, Wind, and SolO. This provides support for the MFR paradigm for CME structure. However, the SolO measurements, which are farthest from the central axis of the MFR, show less defined MFR signatures, presumably due to a greater degree of erosion and degradation of the MFR structure far from its central axis.

astro-ph.SR↗

arXiv2025

How the CME on 21 April 2023 Triggered the First Severe Geomagnetic Storm of Solar Cycle 25

The first severe (G4) geomagnetic storm of Solar Cycle 25 occurred on 23-24 April 2023, following the arrival of a Coronal Mass Ejection (CME) on 23 April. The characteristics of this CME, measured from coronagraphs (speed and mass), did not indicate that it would trigger such an intense geomagnetic storm. In this work, our aim is to understand why this CME led to such a geoeffective outcome. Our analysis spans from the source active region to the corona and inner heliosphere through 1 au using multiwavelength, multi-viewpoint remote sensing observations and in situ data. We find that rotation and possibly deflection of the CME resulted in an axial magnetic field nearly parallel to the ecliptic plane during the Earth encounter, which might explain the storm's severity. Additionally, we find that imaging away from the Sun-Earth line is crucial in hindcasting the CME Time-of-Arrival at Earth. The position (0.39 au) and detailed images from the SoloHI telescope onboard the Solar Orbiter mission, in combination with SOHO and STEREO images, helped decisively with the three-dimensional (3D) reconstruction of the CME.

astro-ph.SR↗

arXiv2024

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

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.

astro-ph.SR↗

arXiv2024

Flux rope modeling of the 2022 Sep 5 CME observed by Parker Solar Probe and Solar Orbiter from 0.07 to 0.69 au

As both Parker Solar Probe (PSP) and Solar Orbiter (SolO) reach heliocentric distances closer to the Sun, they present an exciting opportunity to study the structure of CMEs in the inner heliosphere. We present an analysis of the global flux rope structure of the 2022 September 5 CME event that impacted PSP at a heliocentric distance of only 0.07 au and SolO at 0.69 au. We compare in situ measurements at PSP and SolO to determine global and local expansion measures, finding a good agreement between magnetic field relationships with heliocentric distance, but significant differences with respect to flux rope size. We use PSP/WISPR images as input to the ELEvoHI model, providing a direct link between remote and in situ observations; we find a large discrepancy between the resulting modeled arrival times, suggesting that the underlying model assumptions may not be suitable when using data obtained close to the Sun, where the drag regime is markedly different in comparison to larger heliocentric distances. Finally, we fit the SolO/MAG and PSP/FIELDS data independently with the 3DCORE model and find that many parameters are consistent between spacecraft, however, challenges are apparent when reconstructing a global 3D structure that aligns with arrival times at PSP and Solar Orbiter, likely due to the large radial and longitudinal separations between spacecraft. From our model results, it is clear the solar wind background speed and drag regime strongly affect the modeled expansion and propagation of CMEs and need to be taken into consideration.

physics.space-ph↗

arXiv2023

The Closest View of a Fast Coronal Mass Ejection: How Faulty Assumptions near Perihelion Lead to Unrealistic Interpretations of PSP/WISPR Observations

We report on the closest view of a coronal mass ejection observed by the Parker Solar Probe (PSP)/Wide-field Imager for {Parker} Solar PRobe (WISPR) instrument on September 05, 2022, when PSP was traversing from a distance of 15.3~to~13.5~R$_\odot$ from the Sun. The CME leading edge and an arc-shaped {\emph{concave-up} structure near the core} was tracked in WISPR~field of view using the polar coordinate system, for the first time. Using the impact distance on Thomson surface, we measured average speeds of CME leading edge and concave-up structure as $\approx$2500~$\pm$~270\,km\,s$^{-1}$ and $\approx$400~$\pm$~70\,km\,s$^{-1}$ with a deceleration of $\approx$20~m~s$^{-2}$ for the later. {The use of the plane-of-sky approach yielded an unrealistic speed of more than three times of this estimate.} We also used single viewpoint STEREO/COR-2A images to fit the Graduated Cylindrical Shell (GCS) model to the CME while incorporating the source region location from EUI of Solar Orbiter and estimated a 3D speed of $\approx$2700\,km\,s$^{-1}$. We conclude that this CME exhibits the highest speed during the ascending phase of solar cycle 25. This places it in the category of extreme speed CMEs, which account for only 0.15\% of all CMEs listed in the CDAW CME catalog.

astro-ph.SR↗

arXiv2023

Sequential Small Coronal Mass Ejections Observed In~situ and in White-Light Images by Parker Solar Probe

We reconstruct the morphology and kinematics of a series of small transients that erupt from the Sun on 2021 April 24 using observations primarily from Parker Solar Probe (PSP). These sequential small coronal mass ejections (CMEs) may be the product of continuous reconnection at a current sheet, a macroscopic example of the more microscopic reconnection activity that has been proposed to accelerate the solar wind more generally. These particular CMEs are of interest because they are the first CMEs to hit PSP and be simultaneously imaged by it, using the Wide-field Imager for Solar Probe (WISPR) instrument. Based on imaging from WISPR and STEREO-A, we identify and model six discrete transients, and determine that it is the second of them (CME2) that first hits PSP, although PSP later more obliquely encounters the third transient as well. Signatures of these encounters are seen in the PSP in situ data. Within these data, we identify six candidate magnetic flux ropes (MFRs), all but one of which are associated with the second transient. The five CME2 MFRs have orientations roughly consistent with PSP encountering the right sides of roughly E-W oriented MFRs, which are sloping back towards the Sun.

astro-ph.SR↗

arXiv2022

Coronal mass ejection deformation at 0.1 au observed by WISPR

Although coronal mass ejections (CMEs) resembling flux ropes generally expand self-similarly, deformations along their fronts have been reported in observations and simulations. We present evidence of one CME becoming deformed after a period of self-similarly expansion in the corona. The event was observed by multiple white-light imagers on January 20-22, 2021. The change in shape is evident in observations from the heliospheric imagers from the Wide-Field Imager for Solar Probe Plus (WISPR), which observe this CME for $\sim$ 44 hours. We reconstruct the CME using forward-fitting models. In the first hours, observations are consistent with a self-similar expansion but later on the front flattens forming a dimple. Our interpretation is that the CME becomes deformed at $\sim0.1\ au$ due to differences in the background solar wind speeds. The CME expands more at higher latitudes, where the background solar wind is faster. We consider other possible causes for deformations, such as loss of coherence and slow-mode shocks. The CME deformation seems to cause a time-of-arrival error of 16 hours at $\sim 0.5\ au$. The deformation is clear only in the WISPR observations and, it thus, would have been missed by 1~AU coronagraphs. Such deformations may help explain the time-of-arrival errors in events where only coronagraph observations are available.

astro-ph.SR↗

arXiv2022

Overview of the remote sensing observations from PSP solar encounter 10 with perihelion at 13.3 Rsun

The closest perihelion pass of Parker Solar Probe (PSP), so far, occurred between 16 and 26 of November 2021 and reached ~13.29 Rsun from Sun center. This pass resulted in very unique observations of the solar corona by the Wide-field Instrument for Solar PRobe (WISPR). WISPR observed at least ten CMEs, some of which were so close that the structures appear distorted. All of the CMEs appeared to have a magnetic flux rope (MFR) structure and most were oriented such that the view was along the axis orientation, revealing very complex interiors. Two CMEs had a small MFR develop in the interior, with a bright circular boundary surrounding a very dark interior. Trailing the larger CMEs were substantial outflows of small blobs and flux-rope like structures within striated ribbons, lasting for many hours. When the heliophysics plasma sheet (HPS) was inclined, as it was during the days around perihelion on November 21, 2021, the outflow was over a very wide latitude range. One CME was overtaken by a faster one, with a resultant compression of the rear of the leading CME and an unusual expansion in the trailing CME. The small Thomson Surface creates brightness variations of structures as they pass through the field of view. In addition to this dynamic activity, a brightness band from excess dust along the orbit of asteroid/comet 3200 Phaethon is also seen for several days.

astro-ph.SR↗

arXiv2022

Direct First PSP Observation of the Interaction of Two Successive Interplanetary Coronal Mass Ejections in November 2020

We investigate the effects of the evolutionary processes in the internal magnetic structure of two interplanetary coronal mass ejections (ICMEs) detected in situ between 2020 November 29 and December 1 by Parker Solar Probe (PSP). The sources of the ICMEs were observed remotely at the Sun in EUV and subsequently tracked to their coronal counterparts in white light. This period is of particular interest to the community since it has been identified as the first widespread solar energetic particle event of Solar Cycle 25. The distribution of various solar and heliospheric-dedicated spacecraft throughout the inner heliosphere during PSP observations of these large-scale magnetic structures enables a comprehensive analysis of the internal evolution and topology of such structures. By assembling different models and techniques, we identify the signatures of interaction between the two consecutive ICMEs and the implications for their internal structure. We use multispacecraft observations in combination with a remote-sensing forward modeling technique, numerical propagation models, and in-situ reconstruction techniques. The outcome, from the full reconciliations, demonstrates that the two CMEs are interacting in the vicinity of PSP. Thus, we identify the in-situ observations based on the physical processes that are associated with the interaction and collision of both CMEs. We also expand the flux rope modeling and in-situ reconstruction technique to incorporate the aging and expansion effects in a distorted internal magnetic structure and explore the implications of both effects in the magnetic configuration of the ICMEs.

astro-ph.SR↗

arXiv2020

Modeling the Early Evolution of a Slow Coronal Mass Ejection Imaged by the Parker Solar Probe

During its first solar encounter, the Parker Solar Probe (PSP) acquired unprecedented up-close imaging of a small Coronal Mass Ejection (CME) propagating in the forming slow solar wind. The CME originated as a cavity imaged in extreme ultraviolet that moved very slowly ($<50$ km/s) to the 3-5 solar radii (R$_\odot$) where it then accelerated to supersonic speeds. We present a new model of an erupting Flux Rope (FR) that computes the forces acting on its expansion with a computation of its internal magnetic field in three dimensions. The latter is accomplished by solving the Grad-Shafranov equation inside two-dimensional cross sections of the FR. We use this model to interpret the kinematic evolution and morphology of the CME imaged by PSP. We investigate the relative role of toroidal forces, momentum coupling, and buoyancy for different assumptions on the initial properties of the CME. The best agreement between the dynamic evolution of the observed and simulated FR is obtained by modeling the two-phase eruption process as the result of two episodes of poloidal flux injection. Each episode, possibly induced by magnetic reconnection, boosted the toroidal forces accelerating the FR out of the corona. We also find that the drag induced by the accelerating solar wind could account for about half of the acceleration experienced by the FR. We use the model to interpret the presence of a small dark cavity, clearly imaged by PSP deep inside the CME, as a low-density region dominated by its strong axial magnetic fields.

astro-ph.SR↗

arXiv2020

Detailed imaging of coronal rays with the Parker Solar Probe

The Wide-field Imager for Solar PRobe (WISPR) obtained the first high-resolution images of coronal rays at heights below 15 R$_\odot$ when the Parker Solar Probe (PSP) was located inside 0.25 au during the first encounter. We exploit these remarkable images to reveal the structure of coronal rays at scales that are not easily discernible in images taken from near 1 au. To analyze and interpret WISPR observations, which evolve rapidly both radially and longitudinally, we construct a latitude versus time map using the full WISPR dataset from the first encounter. From the exploitation of this map and also from sequential WISPR images, we show the presence of multiple substructures inside streamers and pseudostreamers. WISPR unveils the fine-scale structure of the densest part of streamer rays that we identify as the solar origin of the heliospheric plasma sheet typically measured in situ in the solar wind. We exploit 3D magnetohydrodynamic models, and we construct synthetic white-light images to study the origin of the coronal structures observed by WISPR. Overall, including the effect of the spacecraft relative motion toward the individual coronal structures, we can interpret several observed features by WISPR. Moreover, we relate some coronal rays to folds in the heliospheric current sheet that are unresolved from 1 au. Other rays appear to form as a result of the inherently inhomogeneous distribution of open magnetic flux tubes.

astro-ph.SR↗

arXiv2020

Morphological Reconstruction of a Small Transient Observed by Parker Solar Probe on 2018 November 5

On 2018 November 5, about 24 hours 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 onboard 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 jet-like 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 jet-like as viewed from 1 au, but the close-in vantage point of PSP/WISPR demonstrates that it is not intrinsically jet-like, but instead has a structure consistent with a flux rope morphology. Based on its appearance in the SOHO and STEREO-A images, the event belongs in the "streamer blob" class of transients, but its kinematic behavior is very unusual, with a more impulsive acceleration than previously studied blobs.

astro-ph.SR↗

arXiv2020

Relating streamer flows to density and magnetic structures at the Parker Solar Probe

The physical mechanisms that produce the slow solar wind are still highly debated. Parker Solar Probe's (PSP's) second solar encounter provided a new opportunity to relate in situ measurements of the nascent slow solar wind with white-light images of streamer flows. We exploit data taken by the Solar and Heliospheric Observatory (SOHO), the Solar TErrestrial RElations Observatory (STEREO) and the Wide Imager on Solar Probe to reveal for the first time a close link between imaged streamer flows and the high-density plasma measured by the Solar Wind Electrons Alphas and Protons (SWEAP) experiment. We identify different types of slow winds measured by PSP that we relate to the spacecraft's magnetic connectivity (or not) to streamer flows. SWEAP measured high-density and highly variable plasma when PSP was well connected to streamers but more tenuous wind with much weaker density variations when it exited streamer flows. STEREO imaging of the release and propagation of small transients from the Sun to PSP reveals that the spacecraft was continually impacted by the southern edge of streamer transients. The impact of specific density structures is marked by a higher occurrence of magnetic field reversals measured by the FIELDS magnetometers. Magnetic reversals originating from the streamers are associated with larger density variations compared with reversals originating outside streamers. We tentatively interpret these findings in terms of magnetic reconnection between open magnetic fields and coronal loops with different properties, providing support for the formation of a subset of the slow wind by magnetic reconnection.

astro-ph.SR↗

arXiv2019

WISPR Imaging of a Pristine CME

The Wide-field Imager for Solar Probe (WISPR) on board the Parker Solar Probe (PSP) observed a CME on 2018 November 01, the first day of the initial PSP encounter. The speed of the CME, approximately 200-300 km s$^{-1}$ in the WISPR field of view, is typical of slow, streamer blowout CMEs. This event was also observed by the 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. Analysis is extended to lower heights by linking the white-light observations to EUV data from AIA, 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 Å, but as a cavity in nominal coronal temperatures such as 193 Å. By comparing this circular, dark feature in 193 Å\ to the dark, white-light cavity at the center of the eruption in WISPR and LASCO, it can be seen that this is one coherent structure that exists prior to the eruption in the low corona before entering the heliosphere and likely corresponds to the core of the magnetic flux rope. It is also believed that the relative weakness of the event contributed to the clarity of the flux rope in WISPR, as the CME did not experience impulsive forces or strong interaction with external structures that can lead to more complex structural evolution.

astro-ph.SR↗