The Maunder minimum (1645–1715 AD) is a representative grand solar minimum with highly depressed sunspot activity and coincident with the “Little Ice Age” on the Earth. Owing to the limited data quality of the currently used solar activity proxies, the cyclic solar activity variations during the Maunder minimum still need to be explored. By analyzing the red equatorial aurorae recorded in Korean historical books in the vicinity of a low-intensity paleo-West Pacific geomagnetic anomaly, we find clear evidence of an eight-year solar cycle during the Maunder minimum. This result provides a new data source on solar activity and a key constraint to theoretical solar dynamo models. It helps understand the generation mechanism of grand solar minima and the solar-terrestrial relations during the Maunder minimum.

How to cite: Yan, L., He, F., Yue, X., Wei, Y., Wang, Y., Chen, S., Fan, K., Tian, H., He, J., Zong, Q., and Xia, L.:  The eight-year solar cycle during the Maunder minimum , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15320, https://doi.org/10.5194/egusphere-egu24-15320, 2024.

A strong correlation between the intensity of chromospheric emissions and the (unsigned) photospheric magnetic field strength has been established in several studies. These studies have typically been based on line-of-sight (LOS) observations of the magnetic field, while measurements of the full 3D magnetic vector, which provide the true field strength and the orientation of magnetic field line, have not been studied in this context. Thus, the possible effect of magnetic field inclination on chromospheric emissions has remained hidden so far.

We study here how the inclination of the photospheric magnetic field, as measured by the full 3D magnetic vector from the Solar Dynamics Observatory (SDO) Helioseismic Magnetic Imager (HMI), affects the FUV emission at around 1600 Å from SDO Atmospheric Imaging Assembly (AIA). We analyze 1168 co-temporal observations by the two instruments from 2014 to 2017. We focus on magnetically active regions outside the sunspots (e.g., plages and network) close to the solar disk center.

We find that the AIA 1600 Å emission typically decreases with increasing (more horizontal) inclination. For all inclinations, AIA 1600 Å emission increases with increasing magnetic field to a maximum emission and then slowly decreases for larger field strengths. Maximum emission and the related field strength decrease with inclination. Above this field strength of maximum emission, the emission decouples from the field strength and is mainly governed by inclination. For fixed AIA emission level the associated magnetic field strength decreases with inclination. The difference in the median magnetic field strength can be more than 200 G (about a factor of two) for the same emission level between almost radial (γ_Loc ≈ 15°) and nearly-horizontal (γ_Loc ≈ 60°) fields.

AIA 1600 Å emission and magnetic field inclination are bimodally distributed with constant magnetic field strength below 1000 G. One population has a high AIA emission and a roughly vertical magnetic field, the other a lower emission and a horizontal field. The population consisting of less bright pixels with horizontal field is typically found at the border of active region, while the population with bright pixels with a vertical field occupy the bulk of an active region.

Our results show that the chromospheric FUV emission at around 1600 Å is strongly influenced by the inclination of the magnetic field. These results are important, for example, for models aiming to reconstruct the solar spectral irradiance or the past solar activity based on chromospheric emissions. These models would be more accurate if they took into account the effect of inclination of the magnetic field on FUV emissivity.

How to cite: Tähtinen, I., Pevtsov, A., Asikainen, T., and Mursula, K.: Effect of magnetic field inclination on SDO/AIA 1600 Å emission, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6368, https://doi.org/10.5194/egusphere-egu24-6368, 2024.

Coronal mass ejections (CMEs) are humongous structures that permeate the heliosphere as they travel away from the Sun. Beginning their journey from a more-or-less localised region in the solar atmosphere, they expand to many times the size of the Sun through the corona, measure about 0.3 au in radial extent by the time they reach 1 au, and interact with the structured solar wind and other transients to form so-called merged interaction regions in the outer heliosphere. One of the most prominent challenges in heliophysics is the achievement of a complete understanding of the intrinsic structure and evolution of CMEs, in particular of their spatiotemporal variability, which in turn would allow more precise forecasts of their arrival time and space weather effects throughout the heliosphere. The most common methods to detect and analyse these behemoths of the solar system consist of remote-sensing observations, i.e. 2D images at various wavelengths, and in-situ measurements, i.e. 1D spacecraft trajectories through the structure. These data, however, are often insufficient to provide a comprehensive picture of a given event, due to the scarcity of available measurement points and the enormous scales involved. Some ways to circumvent these issues consist of taking advantage of multi-spacecraft observations of the same CME (usually at different heliolongitudes and/or radial distances) and to use simulations to complement the available measurements and/or to investigate the 3D structure of CMEs without constraints on the number of synthetic observers.

In this presentation, we will first provide a review of the advantages of multi-spacecraft observations of CMEs and how they have helped us build the overall picture of CME structure and evolution that forms our current understanding. We will then showcase examples of detailed CME studies, both in the observational and modelling regimes, that have been made possible due to the availability of multi-point measurements. These will include events observed remotely and/or in situ by the latest generation of heliophysics missions, i.e. Parker Solar Probe and Solar Orbiter. Finally, we will speculate on possible future avenues that are worthy of exploring to reach a deeper understanding of CMEs from their eruption throughout their heliospheric journey, especially in terms of novel space missions that may improve not only our knowledge from a fundamental physics standpoint, but also our prediction and forecasting capabilities.

How to cite: Palmerio, E.: Analysing CME observations and simulations with multi-spacecraft techniques, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13951, https://doi.org/10.5194/egusphere-egu24-13951, 2024.

The solar wind travels supersonically in the solar system until it reaches the termination shock, where it
is slowed down due to the interplay between the interstellar medium (ISM) and heliosphere. The region
of slowed down solar wind is referred to as the heliosheath, where a great number of mysteries remain
unsolved. Within the SHIELD NASA Drive Center, investigating the physical processes within the
heliosheath and their consequences is a fundamental goal in understanding both the shape of the
heliosphere and also how it protects the solar system from harmful galactic cosmic rays. Here, we
highlight some of the findings of SHIELD: (1) a Rayleigh-Taylor like instability develops in the
heliosheath due to charge exchange, which in turn allows for mixing between the solar wind and ISM
plasma yielding a short, “croissant-like” heliotail; (2) via magnetohydrodynamic modeling, we can
capture this mixing region, which has potential implications for particle acceleration; (3) current
energetic neutral atom (ENA) observations appear to be insufficient for distinguishing the true shape of
the heliotail, but future ENA-focused missions, such as IMAP, will have the capability to determine the
shape of the heliotail; (4) ENA observations of the heliotail and Lyman-alpha observations may also be
able to reveal the properties of the interstellar magnetic field

How to cite: Kornbleuth, M., Opher, M., Powell, E., Onubogu, C., Ma, X., and Richardson, J.: Investigating the Complex Heliosheath of our Heliospheric Shield, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2490, https://doi.org/10.5194/egusphere-egu24-2490, 2024.

Through serendipitous measurements with its plasma wave antennas, the Wind spacecraft recorded more than one hundred thousand impacts of cosmic dust particles onto the spacecraft body. Frequency analysis of the time series of impact data reveals signatures of the solar rotation.

These solar rotation signatures are transient in time. Case studies of time periods with particularly long-lasting corotating interaction regions (CIRs) yield stronger solar rotation signatures in the dust data than case studies of time periods with short-duration CIRs or few CIRs. This indicates that CIRs are a likely cause of the solar rotation signatures, possibly in combination with the alternating sector structure of the solar wind.

One physical mechanism that can cause the solar rotation signature, besides temporary changes of the spacecraft's floating potential that may influence the signal, is a local depletion of dust particles when a CIR passes by the spacecraft. A similar mechanism has been proposed to occur during coronal mass ejections (CMEs) and has been observed in close vicinity to the Sun with Parker Solar Probe. A statistical depletion analysis of the Wind cosmic dust impact data finds that both CMEs and CIRs with strong magnetic fields can locally deplete dust. This effect is strongest for small particles in CMEs.

How to cite: Baalmann, L. R., Péronne, A., Hunziker, S., Strähl, C., Kirchner, J. W., Glaßmeier, K.-H., Chadda, S., Malaspina, D. M., Wilson III, L. B., and Sterken, V. J.: Solar rotation signatures in cosmic dust data measured by the Wind spacecraft, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-388, https://doi.org/10.5194/egusphere-egu24-388, 2024.

Energetic Neutral Atoms (ENAs) from the heliosphere are a unique means to remotely image the boundary regions of our heliosphere. NASA's Interstellar Boundary Explorer (IBEX) has been very successful in measuring these ENAs since 2008 at energies from tens of eV to 6 keV.

The ENA low energy range from tens of eV to solar wind energy (roughly 1 keV) has been sampled throughout an entire solar cycle with the IBEX-Lo ENA imager. This enables us to study the physical implications for the structure of the heliosphere and for the parent proton populations in the heliosheath and other plasma regions that give rise to the observed ENAs. Here, we will discuss in particular the implications of the measured ENA intensities for the plasma pressure balance at the heliospheric boundary.

How to cite: Galli, A., Wurz, P., Schwadron, N. S., Möbius, E., Fuselier, S. A., Sokół, J. M., Bzowski, M., Swaczyna, P., Dialynas, K., and McComas, D. J.: Implications of Energetic Neutral Atoms observed with IBEX-Lo for the pressure balance in the heliosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5343, https://doi.org/10.5194/egusphere-egu24-5343, 2024.

Cosmic dust particles with sufficiently high charge-to-mass ratios interact with the heliosphere on both global and local scales due to the coupling of the charged dust with the heliospheric plasma. They are the fingerprints of heliospheric phenomena, and are tracers that can set boundary conditions to heliospheric models in addition to plasma, magnetic field or other measurements like galactic cosmic rays. 

This talk highlights (1) the synergies between the heliospheric and dust science, (2) the dust model predictions and (3) measurement requirements for dust measurements with an Interstellar Probe in different regions inside and outside of the heliosphere. We discuss how the choice of trajectories and launch date can affect the measurements and the science goals. 

Answering pressing questions concerning the dust-heliosphere interactions requires a multi-mission approach with missions inside the solar system as well. We therefore present interstellar dust impact predictions for the Destiny+ mission, and we illustrate how we aim to infer information about the heliosheath filtering using the data and simulations. 

Finally, we conclude - and highlight with some examples - why heliospheric/plasma physics and dust science go hand in hand, in particular for future mission proposals. We illustrate this with specific examples like the DOLPHIN and SunCHASER mission concepts and an instrument on the Lunar Gateway. 

How to cite: Sterken, V. J., Hunziker, S., Dialynas, K., Baalmann, L. R., Péronne, A., Krüger, H., Strub, P., Cho, K.-S., Carpenter, J. D., Posner, A., and Brandt, P.: Heliospheric and cosmic dust science with Interstellar Probe and with missions inside the solar system, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20141, https://doi.org/10.5194/egusphere-egu24-20141, 2024.

We present new evidence of active magnetic reconnection observed by Voyager-2 in the heliosheath region beyond the termination shock in the outer heliosphere. Multiple cases have been identified in which significant plasma jets are present during heliospheric current sheet crossings, or sector reversals. Using a combination of the plasma and magnetic field measurements from Voyager-2, candidate events are identified by rotating the magnetic field and plasma velocity vector data into a minimum-variance, LMN-coordinate frame, prior to checking consistency with the Walen relation on the corresponding plasma jet. In the LMN frame, the candidate events are selected based on consistency with the expected geometry of current sheets undergoing magnetic reconnection. The Walen relation further supports consistency with the physics of magnetic reconnection, in which the outflow jets of reconnected field and plasma are ejected from the reconnection site at the Alfvén speed. Error analysis based on limitations of the Voyager-2 data is accounted for throughout the process. In this presentation, we detail the event identification and walk through an example case before presenting several other cases. All combined, confirmation of active magnetic reconnection ongoing in the heliosheath has important implications concerning the heating of plasma in the outer heliosphere and the acceleration of pickup ions and possibly even anomalous cosmic rays.

How to cite: Turner, D., Zhao, L., Eriksson, S., Lavraud, B., Richardson, J., and Opher, M.: Evidence of magnetic reconnection observed in the heliosheath by Voyager-2, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13619, https://doi.org/10.5194/egusphere-egu24-13619, 2024.

How to cite: Wen, L. and Jinsong, Z.: The Radial Distribution of Ion-scale Waves in the Inner Heliosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2063, https://doi.org/10.5194/egusphere-egu24-2063, 2024.

We provide a picture of the global dynamics of electrons in the inner heliosphere through the study of non-linear interactions affecting the non-thermal features of the solar wind electron velocity distribution function (VDF).
More than 50 years of in-situ observations of the solar wind have shown that the electron VDF consists of a quasi-Maxwellian core, comprising most of the electrons, and two sparser components, the halo, which is formed by suprathermal and quasi-isotropic electrons, and an escaping beam population, the strahl (Marsch 2006; Halekas et al. 2020).
Recent Parker Solar Probe and Solar Orbiter (SO) observations have confirmed the existence of an additional non-thermal feature: the deficit, i.e., a depletion in the sunward region of the VDF (Berčič et al., 2021a; Halekas et al., 2021). This feature had already been predicted by exospheric models (Lemaire and Scherer, 1971; Maksimovic et al., 2001).
By employing Particle-in-Cell (PIC) simulations, we study electron VDFs that reproduce those typically observed in the inner heliosphere and investigate how the electron deficit contributes to the onset of kinetic instabilities and to heat flux regulation in the solar wind.
The strahl electrons drive oblique whistler waves unstable which scatter them in turn (Verscharen et al., 2019, Micera et al., 2021). Our simulation results show that, as a consequence of these scattering processes, the suprathemral electrons occupy regions of phase space where they fulfil resonance conditions with the parallel-propagating fast-magnetosonic/whistler wave.
The suprathermal electrons lose kinetic energy, resulting in the generation of unstable waves. The sunward side of the VDF, initially depleted of electrons, is thus gradually filled by electrons that are resonant with the triggered whistler waves.
As this initial deviation from thermodynamic equilibrium is reduced, a decrease in the electron heat flux occurs.
Our study provides a mechanism that explains the presence of the regularly observed parallel sunward whistler waves in the heliosphere (Tong et al., 2019), whose origin remains uncertain (Vasko et al., 2020). It also suggests an explanation for recent SO observations of whistler waves, concomitant with distributions in which the three above-described non-thermal features are observed (Berčič et al., 2021b, Coburn et al., 2023).

How to cite: Micera, A., Verscharen, D., Coburn, J., Halekas, J., and Innocenti, M. E.: Modelling near-Sun solar wind electron distribution functions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17259, https://doi.org/10.5194/egusphere-egu24-17259, 2024.

Switchbacks (SBs) are localized structures in the solar wind containing deflections of the magnetic field direction relative to the background solar wind magnetic field. The amplitudes of the magnetic field deflection angles (θ) for different SBs vary from ~40 to ~160-170 degrees. Alignment of the perturbations of the magnetic field (Δ\vec{B}) and the bulk solar wind velocity (\Delta \vec{V}) is observed inside SBs, so that \Delta\vec{V}~\Delta \vec{B} when the background magnetic field is directed toward the sun (if the background solar wind magnetic field direction is anti-sunward then \Delta\vec{V}~-\Delta\vec{B}, supporting anti-sunward propagation in the background solar wind frame). This causes spiky enhancements of the radial bulk velocity inside SBs. We have investigated the deviations of SB perturbations from Alfvénicity by evaluating the distribution of the parameter α, defined as the ratio of the parallel to Δ\vec{B} component of Δ\vec{V} to Δ\vec{V}_A=Δ\vec{B}/sqrt(4π n_i m_i) inside SBs, i.e. α=V_{}/Δ\vec{V}_A (α=Δ\vec{V}/Δ\vec{V}_A when Δ\vec{V}~-Δ\vec{B}), which quantifies the deviation of the perturbation from an Alfvénic one. Based on Parker Solar Probe (PSP) observations, we show that α inside SBs has systematically lower values than it has in the pristine solar wind: α inside SBs observed during PSP Encounter 1 were distributed in a range from ~0.2 to ~0.9 The upper limit on α is constrained by the requirement that the jump in velocity across the switchback boundary be less than the local Alfvén speed. This prevents the onset of shear flow instabilities. The consequence of this limitation is that the perturbation of the proton bulk velocity in SBs with θ>π/3 cannot reach α=1 (the Alfvénicity condition) and the highest possible alpha for an SB with θ=π is 0.5. These results have consequences for the interpretation of switchbacks as large amplitude Alfvén waves.

How to cite: Agapitov, O., Drake, J., Swisdak, M., Choi, K.-E., and Raouafi, N.: Constraints on the Alfvénicity of switchbacks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20892, https://doi.org/10.5194/egusphere-egu24-20892, 2024.

Parker Solar Probe (PSP; launched in 2018) observes the Sun from unprecedented close-in and out-of-ecliptic orbits. The unique and high-resolution data from the Wide-Field Imager for Solar Probe (WISPR) aboard PSP give us new insights about the initiation and early evolution of Coronal Mass Ejections (CMEs) in the inner Heliosphere. We investigate the morphology and propagation behavior of distinct small-scale structures associated with a CME caused by a filament eruption, together with blobs related to the post-CME current sheet. Within this work we want to answer the following questions: how do the small scale magnetic field structures develop, how do they change in shape over time and what is their relation with the erupting filament and flux rope, respectively. The fast PSP motion at perihelion allows one to have views from different angles of the same event, hence we apply a single-spacecraft triangulation technique to derive coordinates and kinematics of each tracked feature. We find distinct groups of small-scale features which appear to be the building blocks of the global CME. We categorised the small scale magnetic structures based on their morphology and extent in longitude and latitude. We obtained a large range of longitudes among the different blobs related to the CME-aftermath. Thread-bundles are identified in the inner Heliosphere, which might be related to the vertical threads that are seen evolving during the filament eruption. Finally, we discuss on the different global appearances of the CME as observed from 1 AU compared to 0.18 AU (PSP).

How to cite: Cappello, G., Temmer, M., Vourlidas, A., Braga, C., Liewer, P., Qiu, J., Stenborg, G., Kouloumvakos, A., Veronig, A., Penteado, P., Bothmer, V., and Chifu, I.: Internal magnetic field structures observed by PSP/WISPR in a filament-related CME event, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16583, https://doi.org/10.5194/egusphere-egu24-16583, 2024.

We report observations of time-intensity profiles, velocity dispersion, pitch-angle distributions, spectral forms, and maximum energies of <500 keV/nucleon suprathermal (ST) H, He, O, and Fe ions in association with eight separate crossings of the heliospheric current sheet (HCS) that occurred near perhelia during Parker Solar Probe (PSP) encounters E7-E15. We find that the ST ion observations fall into three categories, namely: 1) the E07 observations posed serious challenges for existing models of ST ion production in the inner heliosphere; 2) ST observations during 6 separate HCS crossings are consistent with a scenario in which the accelerated ions escape out of sunward-located reconnection exhausts; and 3) a near 4-hr HCS crossing during E14 when PSP traversed regions close to the reconnection exhaust and observed ST protons up to ~550 keV in energy. The reconnection exhaust or the source of these ST ions subsequently moved outside of PSP orbit thus resulting in a >10:1 sunward flow of the accelerated ST ions. We present detailed analysis of the evolution of the pitch-angle distributions and spectral properties during this crossing which have revealed, for the first time, important clues about the nature of ion acceleration via reconnection-driven mechanisms at the near-Sun HCS.

How to cite: Desai, M. and the Parker Solar Probe, ISOIS, FIELDS, and SWEAP Science TE]tams: Suprathermal Ion Acceleration at the Near-Sun Heliospheric Current Sheet Crossings observed by Parker Solar Probe During Encounters 7-15, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2482, https://doi.org/10.5194/egusphere-egu24-2482, 2024.

During Parker Solar Probe’s 16^th orbit, two solar energetic particle (SEP) events were detected by the Integrated Science Investigation of the Sun (ISʘIS). The spacecraft measuring these SEP events were oriented near-perfectly along the same nominal Parker spiral magnetic field line which connected Earth to the solar source for ambient solar wind speeds. Both events were also observed by STEREO and ACE, which provided the opportunity to examine how SEP velocity dispersion, CME shock arrival, energy spectra, and elemental composition varied during transport from 0.65 and 0.76 AU to ~1 AU.

On 17 July 2023, near the southwestern face of the Sun, the solar magnetic active region 13363 underwent considerable evolution which resulted in the largest SEP event of orbit 16 measured by ISʘIS. Two M5.0+ flares at 23:34 and 00:06 UT coincided with a confined prominence eruption and major halo coronal mass ejection (CME). A similar magnetic evolution occurred on 7 August 2023, at the northwestern limb of the Sun, in the solar magnetic active region 13386 when an M1.4 and X1.4 flare at 19:37 and 20:30, respectively, coincided with a confined prominence eruption and large CME.

We utilized a variety of remote observations from GOES, SDO, and SOHO to characterize the magnetic configuration of the local active regions, estimate low coronal temperature, and discuss confined prominence eruptions as a key particle injection source. The notable result from this multi-spacecraft alignment is that SEP fluence appears qualitatively similar at different radial distances, but heavy ions, such as O and Fe, are depleted in comparison to lighter ions during transport.

How to cite: Muro, G. and the Parker Solar Probe team: Orbit 16 observations of SEP events from Parker Solar Probe to STEREO and ACE, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17105, https://doi.org/10.5194/egusphere-egu24-17105, 2024.

In order to improve the predictions of the ambient solar wind plasma at planets, moons, comets, and interplanetary spacecraft, we are conducting a multi-spacecraft investigation to study the spatial variation and temporal evolution of solar wind structures. Here we present our results on the spatial variation by investigating the impact of latitudinal spacecraft-target separation on extrapolation accuracy. Using ballistically propagated bulk velocity datasets of the ACE, STEREO A, Parker Solar Probe, and Solar Orbiter spacecraft, we perform statistical analyses and case studies. Our findings indicate that a separation of even a few degrees in latitude can introduce errors into propagation accuracy and needs to be taken into account when incorporating in-situ measurements into solar wind forecasting. We further investigate the role of the heliospheric current sheet in this phenomenon by utilizing coronal modeling. The results are useful in supporting out-of-ecliptic solar wind observations and for the improvement of propagation models.

How to cite: Biro, N., Opitz, A., Nemeth, Z., Madar, A., Timar, A., and Koban, G.: Latitudinal Variation of the Background Solar Wind in the Inner Heliosphere from Multi-Spacecraft Observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19033, https://doi.org/10.5194/egusphere-egu24-19033, 2024.

Solar wind magnetic holes are small-scale, isolated decreases of the magnetic field strength. They are commonly divided into two types, linear and rotational magnetic holes, based on the rotation of the magnetic field vector from one side of the hole to the other. We present Solar Orbiter, Parker Solar Probem and MESSENGER measurements of magnetic holes from the inner heliosphere (~0.1-1.0 AU) and Cassini measurements from the outer heliosphere (~9 ̶ 10 AU). We compare properties such as rate of occurrence, and distributions of scale size, depth, and amount of magnetic field rotation, and discuss the findings in terms of local generation of magnetic holes, versus transport of magnetic holes generated in the inner heliosphere. We also discuss the relative importance of magnetic holes in interacting with the magnetospheres of planets in the inner and outer heliosphere.

How to cite: Karlsson, T., Trollvik, H., Dimmock, A., Hadid, L., Morooka, M., Volwerk, M., Arró, G., Madanian, H., Callifano, F., Preisser, L., Rojas Castillo, D., and Simon-Wedlund, C.: Solar wind magnetic holes in the inner and outer heliosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3154, https://doi.org/10.5194/egusphere-egu24-3154, 2024.

Coronal Mass Ejections (CMEs) are among the main drivers of geomagnetic storms. 
The intensity of such storms is related to both the amplitude, coherence
and orientation of the magnetic field embedded in the magnetic cloud carried by
the CME, which can be often identified as a Magnetic Flux Rope (MFR).

During their propagation in the Heliosphere, MFRs are subject
to meso/small-scale processes such as magnetic reconnection and interaction with
turbulent fluctuations. The latter arise from solar wind turbulence,
but also include the turbulent sheath region which can form behind the
interplanetary shock driven by the CME.
These processes are difficult to capture in global numerical simulations of
CMEs and are possibly responsible for the rather small magnetic
correlation lengths which have been estimated for magnetic clouds, as short as a few tenth of AU.

We present a new numerical approach that exploits a lagrangian reference frame
to follow the evolution of a MFR via a high-resolution, 2.5D, visco-resistive 
MHD code implementing spherical expansion (Expanding Box Model).
In particular, we simulate the evolution of a low-beta MFR immersed in a
turbulent medium and study the resiliency of the magnetic structure as a
function of the amplitude and correlation length of the surrounding turbulence.
We present preliminary results using different proxies to estimate the evolution
of MFR coherence and helicity.

How to cite: Sangalli, M., Verdini, A., Landi, S., and Papini, E.: MHD simulations of meso-scale processes in an ICME-like Magnetic Flux Rope, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20405, https://doi.org/10.5194/egusphere-egu24-20405, 2024.

Understanding the large-scale structure and evolution of coronal mass ejections (CMEs) is essential for accurately forecasting their space weather impacts at Earth and other planets. There are several open issues concerning the global shape, evolution and magnetic configuration of CME flux ropes as they travel through the heliosphere, notably their deformation, erosion, deflection, rotation and coherence. Extensive progress is currently made in both regimes of observations and modeling. All types of models, being numerical, empirical or analytical, have their advantages and disadvantages. While 3D-MHD models capture the physics of CMEs in detail, very fast models can map the full parameter space and can quickly interpret multipoint CME flux rope observations. With solar cycle 25 on the rise, the spacecraft fleet Parker Solar Probe, Solar Orbiter, BepiColombo, STEREO-A, and several probes at L1 now routinely provide us with multi-spacecraft lineup observations of the same CME event. This makes it possible to combine remote sensing and in situ observations to constrain CME models. However, entirely novel types of observations are driving the field forward now. In June and September 2022, Parker Solar Probe observed CMEs in situ at 0.07 AU, setting new records for the observations of CMEs closest to the Sun. In 2023, STEREO-A acted as the first sub-L1 monitor while passing the Sun-Earth line. In March 2022, Solar Orbiter was able to measure the magnetic flux rope of a CME in situ prior to Earth impact with a long lead time, for the first time in space science history. From early 2025, Solar Orbiter will provide out-of-ecliptic measurements of CMEs, which is a much needed perspective to constrain large-scale CME flux rope models. The PUNCH mission will provide polarized heliospheric images of CMEs, which leads to the exciting possibility to determine the handedness and possibly flux rope type from remote sensing observations. Distant retrograde mission concepts like MIIST and HENON could routinely sample CMEs at spatial separations of 1-10° and 0.01 to 0.1 AU in the 2030s, when also ESA Vigil is expected to start operations.

How to cite: Möstl, C.: On the current understanding of large-scale flux ropes within solar coronal mass ejections, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4025, https://doi.org/10.5194/egusphere-egu24-4025, 2024.

Total solar eclipses offer an unparalleled opportunity to observe the low and middle corona.  As is our tradition, the solar physics team at Predictive Science is predicting the structure of the solar corona for the April 8, 2024 total solar eclipse, using a magnetohydrodynamic (MHD) model of the corona.  The model incorporates thermodynamic transport terms and employs a wave-turbulence-driven (WTD) description of coronal heating and solar wind acceleration.  Our previous coronal predictions employed relaxed MHD solutions corresponding to a boundary condition based on a single photospheric magnetic map, incorporating data that at best was measured 10 to 14 days prior to the eclipse.

This year, we introduce a new paradigm:  A continuously updated prediction based on a time-evolving model.  To accomplish this near-real time description, we have incorporated 3 new elements:  (1) a time-evolving MHD model driven by evolution of the photospheric magnetic field,  (2) an automated method for energizing the non-potential corona near polarity inversion lines that evolve in time, and (3) The Open-source Flux Transport (OFT) model, that assimilates near-real time surface magnetic flux observations from SDO HMI as well as low-latency observations from the Solar Orbiter PHI instrument made away from the Sun–-Earth line.

This presentation will give an overview of the entire prediction effort and describe the time-dependent coronal dynamical features that appear in the solutions.

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., Downs, C., Caplan, R., Mason, E., Ben-Nun, M., Davidson, R., Lionello, R., Palmerio, E., Reyes, A., Riley, P., Titov, V., Torok, T., and Turtle, J.: Prediction of the Structure of the Corona for the 2024 Total Solar Eclipse:  A Continuously Updated Model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4200, https://doi.org/10.5194/egusphere-egu24-4200, 2024.

The sun, solar wind and magnetospheres exhibit non-linear processes that can couple across a broad range of space and time scales. These multiscale processes can be central to the dynamics of far from equilibrium plasmas, where collisionless processes dominate. This talk offers highlights from two interconnected approaches to advancing our understanding of multi-scale processes in solar system plasmas.

From the plasma physics: If sufficient simplifications can be made, we can study the plasma dynamics from first principles. The non-linear scattering and acceleration of energetic particles in current sheets, by wave particle interactions, and in shocks, can be approached from non self-consistent single particle dynamics allowing the full non-linear physics, including low-dimensional chaos, to be considered. The physics of shocks, reconnection, and its interplay with turbulence can be approached by fully kinetic self-consistent simulations, albeit with restrictions on physical dimension and the range of scales resolved. If bursty energy and momentum transport is an emergent process, then it can be captured by reduced models.

From the data: The full dynamics is revealed in all its richness in observations. A wealth of in-situ and remote observations are available from the fastest physical timescales of interest to across multiple solar cycles. In principle, these afford the study of specific physical process such as reconnection and turbulence, and system-scale processes such as the dynamics of magnetospheres, all of which are fully multiscale and non-linear. In practice, determining the physics from observations relies upon establishing robust, reproducible patterns and relationships from multipoint data in these inhomogeneously sampled, non time-stationary systems. As well as providing fundamental physical insights, these can deliver quantitative estimates of space weather risk.

How to cite: Chapman, S.: Multiscale matters: when coupling across multiple scales drives the dynamics of solar system plasmas, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3620, https://doi.org/10.5194/egusphere-egu24-3620, 2024.

Solar flares are known to leave imprints on the magnetic field at the photosphere, often manifested as an abrupt and permanent change in the downward-directed Lorentz force in localized areas inside the active region. Our study aims to differentiate eruptive and confined solar flares based on the vertical Lorentz force variations. We select 26 eruptive and 11 confined major solar flares (stronger than the GOES M5 class) observed during 2011-2017. We analyze these flaring regions using SHARP vector-magnetograms obtained from the NASA's Helioseismic and Magnetic Imager (HMI). We also compare data corresponding to 2 synthetic flares from a delta sunspot simulation reported in Chatterjee et al. We estimate the change in the horizontal magnetic field and the total Lorentz force integrated over an area around the polarity inversion line (PIL) that encompasses the location of the flare. Our results indicate a rapid increase of the horizontal magnetic field along the flaring PIL, accompanied by a significant change in the downward-directed Lorentz force in the same vicinity. Notably, we find that all the confined events under study exhibit a total change in Lorentz force of < 1.8 x 10^22 dyne. This threshold plays an important factor in effectively distinguishing eruptive and confined flares. Further, our analysis suggests that the change in total Lorentz force also depends on the reconnection height in the solar corona during the associated flare onset. The results provide significant implications for understanding the flare-related upward impulse transmission for the associated coronal mass ejection.

How to cite: Maity, S. S., Sarkar, R., Chatterjee, P., and Srivastava, N.: Changes in Photospheric Lorentz Force in Eruptive and Confined Solar Flares, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7182, https://doi.org/10.5194/egusphere-egu24-7182, 2024.

Coronal Mass Ejections (CMEs) remain a focal point of solar and stellar research due to their significant impact on space weather dynamics and exoplanet habitability. Unfortunately, it has so far proven difficult to measure these events on other stars, with only a handful of confirmed detections. 

On the Sun, strong flares (X1-class and above) are almost always accompanied by a CME. This connection has not been found for other stars, where strong flares are regularly detected without a CME counterpart. To investigate this discrepancy we compare resolved solar observations taken from the Swedish 1-m Solar Telescope with disk-integrated Sun-as-a-star observations taken from the HARPS-N solar telescope. We studied two strong X-class flares, one of which was accompanied by a large (halo)CME, and one that was not. While we have successfully detected flare-related signatures in the activity indices and the radial velocity profile in the Sun-as-a-star data, we detect no significant differences between the two flares and no indications of the presence of the CME, despite other works having previously detected CMEs in Sun-as-a-star data.

We propose that the absence of CME signatures in our data is due to a geometric effect. CMEs far enough away from the disk center are likely to be oriented in such a way that they have limited line-of-sight velocity, and thus cannot produce a strong enough Doppler signature. Therefore, we believe that the lack of observed stellar CMEs is at least partly an observational limitation and does not necessarily represent the underlying physical reality.

How to cite: Pietrow, A. G. M., Cretignier, M., Druett, M. K., Alvarado-Gómez, J. D., Hofmeister, S. J., Verma, M., Kamlah, R., Barlatella, M., Amazo-Gómez, E. M., Kontogiannis, I., Dineva, E., Warmuth, A., Denker, C., Poppenhaeger, K., Andriienko, O., Dumusque, X., and Löfdahl, M. G.: Investigating the absence of stellar CMEs through solar observations , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12140, https://doi.org/10.5194/egusphere-egu24-12140, 2024.

This work aims to investigate the long-period oscillations of NOAA12353 prior to a series of C-class flares and to correlate the findings with the 3-5 minute oscillations that were previously studied in the same active region. The objective of this work is to elucidate the presence of various oscillations with long periods in the lower solar atmosphere both before and after the flare events. Understanding the relationship between oscillations in solar active regions and their solar eruption activity is essential. To detect long-period oscillations the emergence, shearing, and total magnetic helicity flux components were assessed from the photosphere to the top of the chromosphere. To analyse the magnetic helicity flux in the lower solar atmosphere, linear force-free field extrapolation was used to construct a model of the magnetic field structure of the active region. Subsequently, the location of long-period oscillations in the active region was probed by examining the spectral energy density of the measured intensity signal in the 1700Å, 1600Å, and 304Å channels of the Atmospheric Imaging Assembly (AIA) of the Solar Dynamics Observatory (SDO). Significant periods of oscillations were determined by means of wavelet analysis. Based on the evolution of the three magnetic helicity flux components, 3-8 hour periods were found both before and after the flare events, spanning from the photosphere to the chromosphere. These 3-8 hour periods were also evident throughout the active region in the photosphere in the 1700Å channel. Observations of AIA 1600Å and 304Å channels, which cover the chromosphere to the transition region, revealed oscillations lasting 3-8 hours near the region where the flare occurred. The spatial distribution of the measured long-period oscillations mirror the previously reported distribution of 3-5 minute oscillations in NOAA12353, seen both before and after the flares. 
This case study suggest that varying oscillation properties in a solar active region could be indicative of future flaring activity.

How to cite: Wisniewska, A., Korsos, M. B., Kontogiannis, I., Soós, S., and Erdélyi, R.: Examination of Magnetic Helicity and Plasma Oscillation Periods in the Active Region NOAA12353 Prior to three C-Class Flares., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-724, https://doi.org/10.5194/egusphere-egu24-724, 2024.