Findings from the Parker Solar Probe (PSP) mission uncover frequent occurrences of small-scale magnetic flux ropes (SMFRs) and switchbacks (SBs - sharp deflection of magnetic field direction with radial velocity spike inside) as structural components of the solar wind. These mesoscale structures are present at all heliocentric distances and are specifically active in the young solar wind. SMFRs exhibit fundamental physical traits akin to larger structures but are distinguished by their notably smaller scale, lasting from seconds to a couple of hours, spanning distances from a few thousand kilometers to several solar radii (Rs). Previous research has identified mesoscale features, including successive SMFRs, blobs, and SBs observed in the inner heliosphere. These observations were made during the PSP's co-rotational orbits with the Sun, aligned radially along a narrow longitudinal zone. By examining these sequential structures, we have determined SB structures at the boundaries of SMFRs. We showed that the cross-occurrence of SBs and SMFRs is significant and these SBs’ geometries are determined by the SMFR orientation. Our findings of switchbacks associated with SMFRs suggest that they are integral to understanding the magnetic topology and the evolution of SBs, influenced by surrounding structures during their propagation. Furthermore, stability assessments are conducted at the boundaries of SMFRs to derive the specific local origin of SBs and factors, which affect their parameters, providing insights into the dynamic processes shaping the young solar wind.
How to cite: Choi, K.-E., Agapitov, O., Lee, D.-Y., Mozer, F., and Huang, J.: Inter-relationships between Small-Scale Magnetic Flux Ropes and Switchbacks in the Young Solar Wind from Parker Solar Probe Observations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13228, https://doi.org/10.5194/egusphere-egu25-13228, 2025.
Parker Solar Probe had its lowest-ever perihelion of 9.86 solar radii on December 24, 2024 ('Encounter 22') and another on March 22, 2025 (Encounter 23). We will present data from these Encounters, focusing on magnetic field measurements, solar connectivity, and Heliospheric Current Sheet (HCS) crossings as the spacecraft crossed nearly halfway around the Sun in just 4 days. We also compare E22/E23 measurements of the radial magnetic field and field magnitude to trends from earlier Encounters showing increasing radially-normalized magnetic flux with altitude. We will review highlights of previous PSP solar encounters and compare to the latest encounters at the lowest-ever perihelion.
How to cite: Bale, S., Badman, S., Ervin, T., Dudok de Wit, T., Goetz, K., Horbury, T., Larson, D., Malaspina, D., Pulupa, M., Rawafi, N., Stevens, M., and Velli, M.: Parker Solar Probe at 9.86 solar radii: magnetic field structure, trends, and connectivity, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4601, https://doi.org/10.5194/egusphere-egu25-4601, 2025.
Solar wind transients such as corotating interaction regions can cause geomagnetic storms. Understanding solar wind conditions throughout the inner heliosphere is crucial for forecasting space weather conditions at Earth and other planets. Recent missions, including Parker Solar Probe (PSP) and Solar Orbiter offer new possibilities for probing the evolution of solar wind properties due to their orbits at various solar distances. We investigate how persistent the solar wind plasma flow is over distance by correlating solar wind parameters measured by spacecraft located at different positions in the heliosphere (0.1AU – 1.5AU). For that, we introduce a new two-dimensional persistence model of the solar wind based on in-situ measurements. Assuming persistence, the measured in-situ parameters from inner spacecraft are being propagated outwards applying the process of inelastic collisions between the plasma parcels. The resulting time-dependent 3D map of solar wind parameters is compared to in-situ data from spacecraft located further away and at different longitudinal positions from the Sun. We present statistics on the comparison between modeled and measured in-situ solar wind plasma parameters across radial distances and temporal evolutions.
How to cite: Milošić, D., Temmer, M., Heinemann, S., Hofmeister, S., Guo, J., and Cao, Y.: Persistence of Solar Wind Characteristics through Radial and Temporal Evolution, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9744, https://doi.org/10.5194/egusphere-egu25-9744, 2025.
The solar magnetic field expands outward from the Sun with the solar wind and fills the heliosphere. Understanding the structure, dynamics, and connectivity of this field underlies many unanswered questions in solar and heliospheric physics. In the presence of ideal flows and in the reference frame co-rotating with the Sun, the solar wind plasma flow is aligned with the magnetic field. In this approximation, tracing the magnetic connectivity of plasma parcels encountered in the heliosphere back to the Sun reveals their solar origin. The magnetic field is also important for the propagation of solar energetic particles (SEPs), guiding them along magnetic field lines from their generation near the Sun to locations in the heliosphere. Models with varying degrees of complexity are used to estimate the magnetic field connectivity and interpret observations. A standard approach is to use potential field models to describe the corona, and to ballistically map points in the heliosphere back to the corona with the in situ measured solar wind speed. More advanced models couple the potential field corona with a heliospheric MHD model. We test the strengths and limitations of these approaches by utilizing a data-driven time-evolving model of the corona and heliosphere, computed for a month of evolution surrounding the 2024 total solar eclipse. The time-evolving model is highly dynamic, with many small-scale eruptions. We treat the time-dependent model as the ``ground truth'' and investigate how well the standard approaches capture the time-varying magnetic connectivity.
Research Supported by NASA and NSF. Computational resources provided by the NSF ACCESS program and the NASA Advanced Supercomputing division at Ames.
How to cite: Linker, J. A., Downs, C., Caplan, R., Lionello, R., Riley, P., Mason, E., and Palmerio, E.: Magnetic Connectivity in the Time-Evolving Heliosphere, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12408, https://doi.org/10.5194/egusphere-egu25-12408, 2025.
Mesoscale structures in the solar wind offer unique insights into its formation, retaining signatures of heating, release mechanisms, and acceleration processes. Plasma heavy ion composition and charge states are critical observables for studying these structures. These properties, established within about 5 solar radii, are preserved as the solar wind propagates, enabling the connection between in situ measurements and their solar sources. Elevated abundance ratios of low first ionization potential (FIP) elements (e.g., Fe/O) and higher charge states are indicative of solar wind originating from active regions and quiet Sun magnetic fields, in contrast to coronal holes. These properties are often structured on mesoscales and can exhibit quasi-periodic behavior, associated with interchange reconnection at the Sun’s open-closed magnetic boundary.
We investigate a multi-day interval from March 4–9, 2022, during which Solar Orbiter’s Heavy Ion Sensor (HIS) observed mesoscale solar wind structures at ~0.49 AU. These structures were confirmed to persist to L1 via ACE and Wind observations, with similar variability in Fe/O and O7+/O6+. Spectral analysis revealed quasi-periodic signals (~30-minute periodicities) in O7+/O6+ ratios during four of the six days analyzed. To link these observations to their solar origins, we used the Wang-Sheeley Arge (WSA) model driven by ADAPT synoptic maps. The model determined solar sources were characterized by parameters empirically related to solar wind formation, such as expansion and squashing factors.
A key feature of this interval was a small stream interaction region (SIR) observed at Solar Orbiter on March 8, coinciding with a connectivity change to a new open-field region bordering a compact active region. This event, confirmed through WSA modeling, corresponded to significant enhancements in Fe/O and O7+/O6+, providing evidence of mesoscale structures linked to active region dynamics. The FIP bias observed in situ (Fe/O) was compared to remote SPICE observations (S/O) at the modeled solar source locations, highlighting challenges in reconciling in situ and remote measurements due to differences in abundance ratio derivations.
Our results demonstrate that mesoscale structures form in active regions via interchange reconnection and survive through the heliosphere, maintaining their composition signatures. This study underscores the value of combining multi-messenger observations and physics-based modeling to trace solar wind origins and reveals the need for enhanced coordination in future heliophysics missions. These findings advance our understanding of solar wind structuring and dynamics, providing a framework for future studies of mesoscale phenomena.
How to cite: Zambrana Prado, N., Wallace, S., Gershkovich, I., Viall, N., Kucera, T., Young, P., Lepri, S., and Yardley, S.: Mesoscale Dynamics in the Solar Wind: Insights from Solar Orbiter and L1 Observations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18482, https://doi.org/10.5194/egusphere-egu25-18482, 2025.
This presentation outlines the Doppler dimming diagnostic method, the computational tools developed, and the solar wind speed maps derived from Metis data spanning a wide range of heliocentric distances, from approximately 1.5 to 10 solar radii, during the solar activity minimum.
The Doppler dimming diagnostic, which combine simultaneous Metis observations from its two channels, polarized broadband visible light and narrowband ultraviolet H I Lyα intensity, allows for the measurement of the expanding coronal plasma speed. The presented wind speed maps are obtained from Metis data sets collected during the cruise phase of the Solar Orbiter mission, shortly after its first perihelion at approximately 0.5 AU in June 2020, as well as before and after its second perihelion in January and February 2021. These observations provide critical insights into the solar corona above approximately 3.0 solar radii, while future Solar Orbiter perihelion passages will extend this analysis to distances as close as 1.7 solar radii.
The reliability of the derived wind speed values is evaluated, considering instrumental uncertainties, the inherent limitations of the diagnostic method, and key assumptions about solar corona model parameters, including electron and neutral atom kinetic temperatures and the 3D geometric configuration of the corona.
As expected at the minimum of the solar cycle, the obtained maps show a clear bipolar topology with a rapid transition to higher speeds in the interface zone between equatorial streamers and high-latitude regions. The equatorial regions, where intense and relatively stable streamer belt persists, do not exhibit speeds higher than 220 km/s up to the maximum observed distance, around 6 solar radii. In contrast, within the coronal holes, already just above the minimum observed heights, around 3.5 solar radii, the wind speed reaches the maximum values detectable using Doppler dimming diagnostics applied to the neutral hydrogen line, approximately 350 km/s.
The method and algorithms are further tested and applied to a sample of daily ultraviolet intensity images reconstructed from spectral data obtained by the UVCS instrument, in conjunction with visible light coronal observations performed by LASCO, both instruments onboard the SOHO mission during solar cycle 23. This extended analysis provides valuable insights into the solar wind acceleration region, covering distances between approximately 1.5 and 4.0 solar radii, encompassing nearly a full solar activity cycle, providing essential context to complement the present Solar Orbiter observations.
How to cite: Giordano, S. M., Spadaro, D., Susino, R., Ventura, R., Romoli, M., Fineschi, S., Zangrilli, L., and Telloni, D.: Solar Wind Speed Maps from the Metis coronagraph observations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19935, https://doi.org/10.5194/egusphere-egu25-19935, 2025.
Many in-situ solar wind observations show a clear correlation between the proton temperature and the bulk speed. Different authors use various formulas to describe this behavior, but one relation over a speed range covering both the slow and fast solar winds is usually sufficient for measurements made at 1 AU. Moreover, the relationship is observed throughout the solar cycle and no significant variations were measured. Therefore, it is commonly used to predict the expected solar wind temperature for a given solar wind speed. The ratio between the expected and measured proton temperature also serves as one of the ICME identifiers since these often have unusually low temperatures. However, the mechanisms leading to the relationship between the proton temperature and speed are not fully understood. It may be the result of solar wind acceleration processes near the Sun, but it may also change during the solar wind propagation, for example due to the stream interactions and/or different ways of energy transfer in solar wind streams coming from distinct source regions. We use observations from the recent inner-heliosphere missions (Parker Solar Probe and Solar Orbiter) and combine them with the near-Earth measurements (WIND, ACE) to study the radial evolution of this relationship. We find that the character of the radial evolution changes significantly at about 0.4 AU from the Sun. We discuss the possibility that the solar wind reaches a nearly collisionless regime near this point, thus we also investigate the effect of the collisional age.
How to cite: Durovcova, T., Satyasmita, S., Safrankova, J., and Nemecek, Z.: Changes of the temperature-speed relationship through the inner-heliosphere, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4812, https://doi.org/10.5194/egusphere-egu25-4812, 2025.
The analysis of directional discontinuities (DDs) in the solar wind provides insights for understanding its embedded structures, such as flux ropes and switchbacks (SBs).
We aim to investigate the occurrence and nature of DDs observed by BepiColombo (BC) close to Mercury’s orbit and to establish links between magnetic field measurements and plasma parameters. Specifically, we assess the potential of DDs as indicators of SBs and other solar wind structures.
We use the attitude gradient to detect discontinuities combined with minimum variance analysis to characterize their boundaries.
During the selected period between 5 and 16 October 2021, a total of 1136 DDs were identified, with 960 meeting the eigenvalue ratio criterion for classification. The majority (83%) were rotational discontinuities (RDs) or either discontinuities (EDs). Low compressibility (CB < 0.03) conditions yielded a higher proportion of RDs and EDs (94%). PICAM observations revealed significant ion energy enhancements and particle deflections correlated with magnetic field reversals, particularly during SBs structures with low compressibility.
The results confirm the suitability of attitude gradient-based methods for DD detection and the potential of CB and z as proxies for identifying quasi-Alfvénic structures. The combined analysis of magnetic and plasma data highlights the role of DDs as markers of SBs, advancing our understanding of their nature and prevalence in the solar wind at 0.34 AU.
How to cite: Di Bartolomeo, P. P., Stumpo, M., Benella, S., Alberti, T., Milillo, A., Varsani, A., Heyner, D., Aronica, A., Jeszenszky, H., Kazakov, A., Noschese, R., Gunter, L., Plainaki, C., Moroni, M., and Giovannelli, L.: Detecting in-situ directional discontinuities in the solar wind at Mercury's Orbit, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6400, https://doi.org/10.5194/egusphere-egu25-6400, 2025.
How to cite: Wu, Z., He, J., and van Doorsselaere, T.: Multi-point observations and eigenmode instability analysis of tearing-induced reconnection in the heliospheric current sheet related to primary solar wind, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14938, https://doi.org/10.5194/egusphere-egu25-14938, 2025.
How to cite: Varesano, T., Hassler, D., and Zambrana-Prado, N.: Investigating the Origins of the Solar Wind: Understanding Plasma Composition and Fractionation with Solar Orbiter SPICE, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5841, https://doi.org/10.5194/egusphere-egu25-5841, 2025.
During its encounter, Parker Solar Probe can sample the plasma outflow from the Sun in periods of corotation, allowing us to follow the solar wind during its radial evolution. We analyze plasma and magnetic field properties in two periods of corotation when Alfvènic streams of the solar wind were sampled. These data are then compared with results of a solar wind model.
In particular, the numerical model is an updated version of VPE (Grappin et al. 2011 ApJ) that solves one one-dimensional MHD equations including radiation and conduction, with separate proton and electron temperatures. Integration starts from the chromosphere and reaches PSP orbit and beyond. Magnetic and velocity fluctuations are also injected from the chromosphere and can contribute to the heating of the solar wind via a phenomenological turbulent dissipation (VPEW model).
We use measurements to constrain several free parameters of the model, namely the chromospheric density, the magnetic field intensity and expansion, the fluctuations amplitude, and the turbulent phenomenology, and discuss their implications for the plasma properties closer to the Sun and for the heating and acceleration of the solar wind.
How to cite: Verdini, A., Grappin, R., Landi, S., and Franci, L.: Constraints on the heating and acceleration of Alfvénic streams using Parker Solar Probe data and a two-temperature solar wind model, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10252, https://doi.org/10.5194/egusphere-egu25-10252, 2025.
As the solar wind expands in the inner heliosphere, the evolution and relaxation of the electron velocity distribution function (eVDF) is governed by a complex interplay of collisional and collisionless processes.
This study investigates with numerical simulations the competition between Coulomb collisions and the electron firehose instability (EFI) - a kinetic instability arising under anisotropic pressure conditions - during the isotropization of the electron VDF.
The goal is to gain deeper insights into how collisional and collisionless processes influence each other in this regime.
Fully kinetic simulations are run using the particle-in-cell (PIC) code OSIRIS, in the presence and absence of Coulomb collisions.
The plasma density (and hence the collisional frequency) is progressively increased in the presence of collisions to investigate solar wind regions progressively closer to the Sun.
How to cite: Völp, J., Schoeffler, K., Tenerani, A., and Innocenti, M. E.: PIC simulation of the competition of collisional and collisionless processes in the relaxation of the electron velocity distribution function in the young solar wind, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12695, https://doi.org/10.5194/egusphere-egu25-12695, 2025.
A global electric potential arises within the solar wind due to the mass disparity between electrons and protons, coupled with the constraints of charge quasi-neutrality and zero-current conditions on sufficiently large scales in the heliosphere. This so-called ambipolar electric potential may account for at least part of the solar wind acceleration. Recent findings from the Parker Solar Probe (PSP) reveal that the slow solar wind, with terminal velocities averaging around 250 km/s, could be entirely explained by the ambipolar electric potential. However, an additional, yet unidentified mechanism is required to explain the acceleration of the fast solar wind.
Since the first in situ solar wind observations in 1959, neither magnetohydrodynamic nor kinetic models have been able to consistently account for the fast solar wind acceleration. Therefore, the processes responsible for this additional acceleration remain one of the most significant open questions in space physics. To address this challenge, we propose a pathway to account for the unexplained acceleration by incorporating velocity space diffusion of particles within the kinetic exospheric framework, which self-consistently determines the ambipolar electric potential. This was achieved for electrons by redistributing particles within regions of velocity space defined by the kinetic exospheric approach to account for a diffusion that would occur in the solar wind due to collisions or wave-particle interactions. These are therefore incorporated indirectly in the kinetic exospheric model through diffusion which inevitably fills regions of velocity space that would otherwise remain inaccessible and are thought to be the primary mechanisms behind the formation of the so-called halo population—higher-energy electrons that, unlike the strahl, are not predominantly directed an-sunward.
The recent discovery of the sunward deficit, predicted by the kinetic exospheric models, showed an anticorrelation between the electric potential and the solar wind terminal velocity, potentially implying that the electric potential is only a minor acceleration mechanism for the fast solar wind. We here find that even without the influence of velocity space diffusion, the same anticorrelation can be obtained by our kinetic exospheric model, from observationally derived input coronal temperatures, for a range of heliocentric distances typically sampled by PSP (above 13 Rs). This suggests that the electric potential might still be of major importance to explain the fast solar wind acceleration.
How to cite: Péters de Bonhome, M., Pierrrard, V., and Bacchini, F.: Solar Wind Acceleration Driven by Velocity Space Diffusion and the Ambipolar Electric Potential, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16263, https://doi.org/10.5194/egusphere-egu25-16263, 2025.
The solar wind and planetary magnetospheres provide excellent natural laboratories to study the basic physics of collisionless plasmas. In these systems, microscopic plasma physics often influences, or even controls, global plasma dynamics by controlling transport of energy and momentum. Electromagnetic fluctuations and the resulting wave-particle interactions are particularly omnipresent. Typical spectra of electromagnetic fluctuations in the solar wind are power laws in frequency, with multiple characteristic breaks signaling changes in the origin of fluctuating modes, as well as onset of dissipation. At frequencies above the electron cyclotron frequency, fluctuations become purely electrostatic, and a persistent level of broadband electrostatic noise is often observed.
High-resolution measurements reveal that these small-scale modes often contain highly coherent wave-packets and solitary structures, the latter likely being electron or ion phase space holes of a few tens of Debye length in size. These bipolar electric field structures can be weak double layers (WDLs), a localized and stable charge separation sustaining a net potential drop across. WDLs are often associated with particle acceleration and energy dissipation.
We present here a preliminary work in which we analyze data from various missions to search for and detect electrostatic solitary waves and WDLs in the inner heliosphere from the solar corona to 1 AU using electric field measurements from Parker Solar Probe, Solar Orbiter, MMS and Wind. Do WDLs observed in the near-Sun solar wind have finite potential drops oriented radially so as to slow escaping electrons and accelerate escaping ions?
How to cite: Salem, C., Bonnell, J., Pulupa, M., Chust, T., Le Contel, O., Jeandet, A., Malaspina, D., and Maksimovic, M.: Observations of Coherent Electrostatic Solitary Waves in the Inner Heliosphere , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20530, https://doi.org/10.5194/egusphere-egu25-20530, 2025.
Strong perpendicular diffusion of the beam in ion VDFs have been detected in the solar wind using Parker Solar Probe's SPAN-i instrument and have been termed as the hammerhead distribution functions. There have been ongoing studies trying to simulate the formation of these hammerhead features, which have met with muted success. It has been hypothesized that these perpendicular scattering of ions can be attributed to resonant scattering of beam ions by parallel-propagating, right circularly polarized, fast magnetosonic/whistler waves (Verniero et al 2022). However, in order to extract definitive physical explanations and stipulate their occurrence rate as a function of plasma beta, closeness to the heliospheric current sheet and distance from change in magnetic topology, a statistical study and characterization is necessary of these hammerhead occurrences. In our study, we develop a super-fast Python-based repository to filter-out the hammerheads across all PSP data where the VDF is dominantly in the field-of-view of SPAN-i. Immediate future goals involve characterizing these hammerhead VDFs using more sophisticated fitting algorithms (sidestepping the bi-Maxwellian fits) to characterize various features of the distributions such as the distance between core and hammerhead, ratio of the parallel and perpendicular temperatures of the core and hammerhead, and other crucial features
How to cite: Das, S. B. and Verniero, J.: Hunting for hammerheads occurances using hammerhead finder software hampy, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15609, https://doi.org/10.5194/egusphere-egu25-15609, 2025.
Localized deflections in the interplanetary magnetic field, often accompanied by enhancements in solar wind velocity and disrupt the idealized Parker spiral topology that is otherwise dictated by the speed of the solar wind plasma flow. Such events, historically referred to by terms such as jets, velocity spikes, or the most recent adopted name magnetic switchbacks, were first observed in 1995 with Ulysses at 2.4 au. The reanalysis of Helios (1976) in 2018 confirmed their presence at smaller heliospheric distances (0.3 au). Their infrequent occurrence at these distances initially led to the belief that they are rare. This perspective changed dramatically with Parker Solar Probe’s (PSP) approach to 0.16 au in 2018, shortly after its launch, revealing an abundance of these deflections within smaller heliodistances. This sparked a significant interest within the scientific community to investigate their properties, possible sources, and significant processes inside the solar corona. However, this new interest also brought forth challenges, as their properties, origin, and behaviour across different radial distances remain unclear, and the lack of a unified definition leaves the subject open to interpretation. For our analysis, after careful consideration of the different properties of switchbacks, literature review, and comparisons between different studies we have constructed a set of criteria based on which we collected a small catalogue of switchbacks. The data considered are from different PSP encounters spanning the minimum, ascending phase, and maximum of the current solar cycle. We present our preliminary analysis, focusing on characteristics such as the direction of the magnetic field vector, and its magnitude, the plasma speed, density, and temperature, and the strahl electron pitch angle distribution.
How to cite: Gülay, E. and Asvestari, E.: Preliminary Results of Switchback Analysis in Parker Solar Probe Observations near the Sun, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11776, https://doi.org/10.5194/egusphere-egu25-11776, 2025.
We present the study of a radial alignment between Parker Solar Probe and Solar Orbiter occurring at the end of April 2021. The two spacecraft were respectively at ~0.075 and ~0.9 au from the Sun. With the help of a propagation method, we identified the same density structure crossing both spacecraft, with a time delay of ~138 h between the two. This density structure is part of the heliospheric plasma sheet. We found that for this event, in-situ density measurements were concordant with radial gradients, while the magnetic field measurements were more concordant with longitudinal gradients. The structure is moreover inferred to have been generated by interchange reconnection in the high corona (2-3 solar radii), as observations are not in agreement with a generation by reconnection of the solar wind open field lines.
How to cite: Demoulin, P., Berriot, E., Alexandrova, O., Zaslavsky, A., Maksimovic, M., and Nicolaou, G.: Parker Solar Probe - Solar Orbiter radial alignment study: evolution of the heliospheric current sheet, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12793, https://doi.org/10.5194/egusphere-egu25-12793, 2025.
Since Parker, the existence of the solar wind has been ascribed to the fact that the solar corona is not in hydrostatic equilibrium and thus is constantly expanding. However, the mechanism responsible for accelerating/heating the solar wind is widely debated, even though there is evidence that it is magnetic in nature. New space missions like Parker Solar Probe (PSP), Solar Orbiter (SolO) and BepiColombo (BC), being much closer to the Sun, allow observations of less evolved and less mixed solar wind. Thus, for example, the observed streams can be easily back-propagated to their source on the Sun, allowing generally more accurate characterizations. These new observations revealed that the measured magnetic field is highly structured close to the Sun, exhibiting patches of large and intermittent reversals associated with jets of plasma. Jetting activity reveals that the solar wind emission is discrete in nature rather than homogeneous, leading to intermittent/impulsive outflow from the corona driven by small-scale magnetic reconnection. In a recent work, it has been shown that super granulation structure at the coronal base remains imprinted in the near-Sun solar wind, resulting in the magnetic polarity inversions known as switchback. Farther from the Sun, however, switchbacks are less frequent, probably due to mixing and turbulent decay.
According to the Potential Field Source Surface extrapolation between 6th and 7th October 2021, BC and SolO were connected to the same region on the Sun. BC and SolO were located at 0.36 AU and 0.67 AU, respectively. Both spacecraft detected a patch of switchbacks, offering the opportunity to investigate their evolution with solar wind propagation. Our findings highlight the potential of BC for synergistic studies with PSP and SolO, despite its primary focus on Mercury’s environment.
How to cite: Stumpo, M., Di Bartolomeo, P. P., Benella, S., Larosa, A., Nicolaou, G., Pezzi, O., Trotta, D., Alberti, T., Milillo, A., Heyner, D., and D'Amicis, R.: Joint observations of magnetic switchbacks from BepiColombo and Solar Orbiter in the inner heliosphere, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18403, https://doi.org/10.5194/egusphere-egu25-18403, 2025.
How to cite: Zhuo, R., Wu, Z., Ma, M., He, J., and Xiong, M.: Propagation of density fluctuations in the near-Sun environment inferred from radio sounding during Tianwen-1 solar conjunction, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15009, https://doi.org/10.5194/egusphere-egu25-15009, 2025.
Previous studies on the interaction of Mars’ un-magnetized space environment with the solar wind have shown that the structural morphology of Mars’ hybrid magnetosphere and the plasma dynamical processes occurring within are strongly driven by its solar wind conditions. This unique interaction is highly complex during quiet solar wind periods, let alone extreme solar wind conditions such as the encounter of CMEs or other transient solar wind structures. This emphasizes the importance of accurate knowledge of the upstream solar wind conditions when any spacecraft is inside the hybrid magnetosphere. However, all planetary missions to Mars consist of only one spacecraft, which further highlights the need for a solar wind model to accurately predict the upstream solar wind conditions. Here, we aim to validate and assess the capability of the physics-based Alfvén Wave Solar atmosphere Model (AWSoM) developed at the University of Michigan in predicting the solar wind interplanetary magnetic field (i.e. B) and plasma conditions (i.e. velocity, temperature and density) by comparing its simulated outputs with the solar wind data from the MAVEN spacecraft; MAVEN has been in orbit around Mars since 2014. We surveyed and identified multiple Carrington rotations across 10 years of MAVEN solar wind observations whenever MAVEN is upstream of the martian bow shock, and compared them with the simulated outputs from AWSoM using the dynamic time warping technique as a metric tool. Preliminary results indicate that AWSoM was able to accurately predict the magnitude of each solar wind parameter but did not perform as well when predicting the time of occurrence for observed solar wind structures (i.e. time-shift between observed and simulated). We further investigated the quality of our data-model comparison between consecutive solar maximum of Solar Cycle 24 and current Solar Cycle 25, and the solar minimum in-between. The data-model comparison methods and results presented in this study contribute to the overall space weather efforts to improve the accuracy and precision of the physics-based AWSoM solar wind predictions over large heliocentric distances, including Mercury and Earth.
How to cite: Poh, G., Gruesbeck, J., Sachdeva, N., Huang, Z., and DiBraccio, G.: Validation of the AWSoM Solar Wind Magnetic Field Model with Upstream Mars Solar Wind Conditions from MAVEN Observations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13763, https://doi.org/10.5194/egusphere-egu25-13763, 2025.
Recurring Coronal Holes (CHs) are long-lived structures in the solar corosna that survive over multiple solar rotations. They are sources of open magnetic field and fast solar wind streams filling the interplanetary space. Of the recurring CHs, those that can generate geomagnetic activity are particularly important due to the recurring impact they can have on the terrestrial environment. In this study we focus on reconstructing their vertical structure and assess how that changes with each rotation. To facilitate our study, we utilized the Potential Field Source Surface (PFSS) and the Schatten Current Sheet (SCS) model incorporated in the coronal modelling domain of EUHFORIA (European Heliospheric Forecasting Information Asset). We investigate the optimal parameter space for model initiation for each CH, compare the model output both to EUV and coronagraph white-light emissions, and assess the reconstructed heliospheric conditions using in situ measurements from different positions throughout the inner heliosphere.
How to cite: Asvestari, E., Heinemann, S., Temmer, M., Milošić, D., Gulay, E., and Pomoell, J.: Reconstructing the evolution of recurring coronal holes in space and time, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15393, https://doi.org/10.5194/egusphere-egu25-15393, 2025.
Solar wind modeling with the 3D MHD model EUHFORIA (EUropean Heliospheric FORecasting Information Asset; Pomoell & Poedts, 2018) revealed discrepancy with in situ observations by the Parker Solar Probe (PSP) at near-Sun distances . The default coronal model employed in EUHFORIA consists of the potential field source surface extrapolation (PFSS), Schatten current sheet (SCS) model and semi-empirical WSA model, which simulate the plasma and magnetic conditions at the inner boundary (0.1 AU). Parameters such as the PFSS source surface height (RSS), which is the outer boundary of PFSS, and the inner boundary of SCS model influence the modelled coronal hole areas and the associated open flux areas. A default RSS value of 2.6 R⊙, as per McGregor et al. (2008), is used in EUHFORIA for solar wind simulations. Lowering the RSS value has been reported to better capture coronal hole areas (Asvestari et al., 2019), improve the reconstruction of small-scale features (Badman et al., 2020), and more accurately reflect coronal magnetic field topologies during different phases of solar cycles (Lee et al., 2011; Arden et al., 2014).
In this parameter study we investigate the possible systematic effects of changing the outer boundary of the PFSS model and the inner boundary of the SCS model, while keeping default values for other parameters. The resulting solar wind simulations are compared to those obtained using all default parameters in the model, by evaluating their agreement with the in situ observations from PSP for its first ten perihelion encounters. Although we found improved modeling accuracy for several time intervals, first results do not show clear systematic improvements in the accuracy of the modeled solar wind.
How to cite: Valliappan, S. P. and Magdalenic, J.: Investigation of Source Surface Height Variations in EUHFORIA and Their Impact on Solar Wind Predictions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16626, https://doi.org/10.5194/egusphere-egu25-16626, 2025.
The solar wind expands outward from the solar corona, defining the interplanetary medium through which coronal mass ejections (CMEs) and solar energetic particles (SEPs) propagate. Accurate models of this ambient solar wind and its embedded magnetic fields are crucial for heliophysics and space weather research. Studies have highlighted the importance of ambient solar wind modeling for accurate CME arrival time predictions. However, comparisons of in situ spacecraft measurements to model solutions at L1 show that state-of-the-art models often perform comparably to a simplistic assumption that solar wind conditions at L1 repeat every 27 days. Here we study why state-of-the-art models often exhibit such surprisingly large errors. Going deeper than previous validation studies, we examine the physical reasons for erroneous predictions on an event-by-event basis by comparing imaging and in-situ observations with simulation results, and provide possible strategies to address these challenges. We study how magnetic structures at coronal hole boundaries, such as streamers and pseudo-streamers, affect model outcomes, among many other experiments. We also study how the choice of ADAPT maps could be crucial in the context of solar wind modelling. We demonstrate our recommendations for improving ambient solar wind modeling through the Wang-Sheeley-Arge (WSA) framework, as implemented by Reiss et al. (2019, 2020). Our findings highlight the different sources that could lead to erroneous predictions, how we can improve the predictions, and the critical need to better constrain magnetic models with observational data to enhance our ambient solar wind modeling capabilities. Moving forward, such improvements are vital for advancing the reliability of space weather forecasting, ultimately protecting astronauts and technological assets in space.
How to cite: Majumdar, S., Reiss, M., Muglach, K., and Arge, C. N.: Identifying and Correcting Errors in Ambient Solar Wind Modeling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15901, https://doi.org/10.5194/egusphere-egu25-15901, 2025.
I analyse the spatial distribution of solar wind sources and relate them to the properties of the interplanetary wind by means of an extended time series of data-driven 3D simulations that cover more than two solar activity cycles. Magnetic connectivity jumps are related with solar wind plasma signatures and with topological features of the global magnetic field. The occurrence frequency and amplitudes if such connectivity jumps vary with the epoch of the solar cycle and on the distance to the ecliptic plane.
The same solar wind model (Multi-VP) constitutes the core of the SWiFT-FORECAST service, based on model pipeline initially developed in the scope of the H2020 SafeSpace project, and later integrated on ESA's SWESNET and on the Virtual Space Weather Modelling Centre. Ensemble forecasts are produced at a daily cadence and with a lead time of a few days. I will address some of the main challenges related to the implementation and validation of these models and pipelines, as well as the pernicious issues that stem from the lack of observables between the two boundaries of the Sun–Earth system, and from the dependence of "point" forecasts on the global properties of the solar atmosphere.
How to cite: Pinto, R.: From multi-decadal solar wind modelling to real-time forecasting, and on moving away from the ecliptic plane, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17463, https://doi.org/10.5194/egusphere-egu25-17463, 2025.
A faster than real time forecast system for solar wind and interplanetary magnetic field transients that is driven by hourly updated solar magnetograms is proposed to provide a continuous nowcast of the solar corona (<0.1 AU) and 24-hours forecast of the solar wind at 1 AU by solving a full 3-D MHD model. This new model has been inspired by the concept of relativity of simultaneity used in the theory of special relativity. It is based on time transformation between two coordinate systems: the solar rest frame and a boosted system in which the current observations of the solar magnetic field and tomorrow's measurement of the solar wind at 1 AU are simultaneous. In this paper we derive the modified governing equations for both hydrodynamics (HD) and magnetohydrodynamics (MHD) and present a new numerical algorithm that only modifies the conserved quantities but preserves the original HD/MHD numerical flux. The proposed method enables an efficient numerical implementation, and thus a significantly longer forecast time than the traditional method. The detailed description of numerical algorithm may be found in https://doi.org/10.48550/arXiv.2501.07222.
How to cite: Sokolov, I. and Gombosi, T.: Physics-Based Forecasting of Tomorrow's Solar Wind at 1 AU, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14389, https://doi.org/10.5194/egusphere-egu25-14389, 2025.
Posters virtual: Thu, 1 May, 14:00–15:45 | vPoster spot 3
EGU25-6031 | ECS | Posters virtual | VPS27
The ion-proton differential streaming observed in Small-scale Flux RopesThu, 01 May, 14:00–15:45 (CEST) | vP3.16
Heavy ion composition and charge-state distributions provide valuable information about the source region of the solar wind due to the 'freeze-in' effect, making them valuable diagnostics for understanding the conditions of their source regions. Small-scale flux ropes (SFRs) have been studied for decades, but their source regions and formation mechanisms are still under debate. While heavy ion signatures in relatively large-scale flux rope structures, known as magnetic clouds (MCs), have been well studied, those signatures are still unclear in SFRs that last only couple of minutes. More importantly, heavy ions do not necessarily travel at the same speed as protons in the solar wind. A potential ion-proton differential velocity could cause a temporal lag between the heavy ion signal and the boundaries of SFRs, which introduces deviations when heavy ion signatures in SFRs are investigated.
In this study, we review ten years of in-situ solar wind heavy ion data obtained from the Solar Wind Ion Composition Spectrometer (SWICS) on board the Advanced Composition Explorer (ACE). The data set is derived from the Pulse Height Analysis (PHA) data, at 12-min resolution. By investigating every energy per charge step of each SWICS measurement interval, more SFRs with short duration, even shorter than 12 minutes, are included. We conduct a statistical study on the ion-proton differential streaming in over 6300 SFRs that are heavy ion abundant, as well as in the surrounding solar wind.
Positive ion-proton differential streaming is found common in SFRs but less common in SFRs that are located in recorded Interplanetary Coronal Mass Ejections (ICMEs) . About 50% heavy-ion-dense SFRs show ion-proton differential velocity larger than 0.2 times the local Alfvén speed. Positive ion-proton differential streaming has also been observed in the background solar wind near SFRs. However, some cases show strong positive ion-proton differential streaming exclusively within SFRs. Ion-proton differential streaming is crucial for understanding heavy-ion signatures in small-scale structures, with their acceleration mechanisms being of particular interest. A further study shows that SFRs detected at 1 AU are unlikely to be the interplanetary manifestations of nanoflare- or microflare-associated small CMEs, or at least not solely so.
How to cite: Gu, C., Heidrich-Meisner, V., and Wimmer-Schweingruber, R. F.: The ion-proton differential streaming observed in Small-scale Flux Ropes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6031, https://doi.org/10.5194/egusphere-egu25-6031, 2025.
