Radio emissions excited by semi-relativistic electrons that are accelerated into the heliosphere by solar flares and CME-driven shocks are abundant, intense, and observed across various solar longitudes. We have shown that radio photons are highly-susceptible to anisotropic scattering off small-scale heliospheric density fluctuations. While such influence on the emitted radio photons significantly complicates their analysis, interpretation, and ability to extract the true physical properties from the observations, it also makes radio emissions a powerful and unique diagnostic of the heliospheric environment. This talk will showcase some of the fascinating diagnostic capabilities of solar radio bursts that make them beneficial to various heliosphysics disciplines. Such bursts have historically been used to obtain information on the exciters of the associated electrons and the acceleration mechanisms. However, recent studies demonstrated that solar radio bursts can also be used to diagnose the level and anisotropy of heliospheric density fluctuations, trace the configuration of the magnetic field, and even reveal the presence of magnetic switchbacks. They also constitute an asset in forecasting solar energetic particles (SEPs) and are thus an integral part of several space weather models.

How to cite: Chrysaphi, N.: The diagnostic power of heliospheric radio emissions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22046, https://doi.org/10.5194/egusphere-egu26-22046, 2026.

In my ERC-AdG project ‘Open SESAME’ (project No 101141362), we aim to develop a time-evolving model for the entire solar atmosphere, including the chromosphere and transition region, based on a multifluid description. Currently, models are primarily steady, rely on a single-fluid description and include only the corona due to computational challenges. We plan to use time-evolving ion-neutral and ion-neutral-electron models. The multifluid approach will enable us to describe the intricate physics in the partially ionised chromosphere and quantify the transfer of momentum and energy between the atmospheric layers. The questions of where the solar wind originates and how solar flares and coronal mass ejections are driven have fundamental scientific importance and substantial socio-economic impact.

This goal is now achievable by combining our implicit numerical solver with a high-order flux reconstruction (FR) method. The implicit solver enables larger time steps, avoiding the numerical instabilities that lead to strict time-step limitations in explicit schemes. The high-order FR method enables high-fidelity simulations on very coarse grids, even in zones of high gradients. We will introduce three critical innovations. First, we will combine high-order FR with physics-based r-adaptive (moving) unstructured grids, redistributing grid points toward regions with high gradients while preserving the HPC cluster's load-balancing. Second, we will implement CPU-GPU algorithms for the new heterogeneous supercomputers advanced by HPC-Europa. Third, we will implement AI-generated magnetograms to enable the model to respond to the time-varying photospheric magnetic field, which is crucial for understanding key properties of the solar plasma and processes.

Thus, we will develop a first-in-its-kind high-order GPU-enabled 3D time-accurate solver for multifluid plasmas. If successful, we will implement the most advanced data-driven solar atmosphere model in an operational environment. The project commenced on September 1, 2024, and we have already obtained interesting results in time-dependent full-MHD corona modelling, inclusion of the TR, AI-generated magnetograms (for the far side of the Sun), and high-order flux reconstruction simulations.

How to cite: Poedts, S. and the Open SESAME: Including the transition region and chromosphere in a global model for the solar atmosphere, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3309, https://doi.org/10.5194/egusphere-egu26-3309, 2026.

We present a first record of significantly enhanced occurrences of magnetic reconnection exhausts as measured by the Wind satellite across a stream interaction region (SIR) at 1 AU from 10:11:20 UT on 4 Jan 2019 to 09:58:00 UT on 5 Jan 2019. The activity is clustered in a slow wind compression regime ahead of the SIR interface with a deflected, compressed fast wind. The 43 exhausts of this 1-day SIR dominate a distribution of 71 exhausts as obtained by a multi-window sliding technique application to the 8-day period on 1-9 Jan 2019. Active current sheets inside the SIR are associated with normal directions mostly near the ecliptic plane and a more azimuthal-than-Parker magnetic field direction at 1 AU. We find that exhausts wider than 500 ion inertial lengths are typically present just upstream and inside this SIR rather than within unperturbed slow and fast winds beyond a shocked solar wind. The observations suggest that plasma and field compressions may be crucial elements in driving a break-up of large-scale current sheets embedded in SIRs into smaller, multi-layered current sheet segments through magnetic reconnection.

How to cite: Eriksson, S., Chasapis, A., Mallet, A., and Swisdak, M.: Ubiquitous Occurrences of Multi-scale Layers of Magnetic Reconnection across a Solar Wind Stream Interaction Region at 1 AU, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-68, https://doi.org/10.5194/egusphere-egu26-68, 2026.

While quasi- perpendicular shocks are commonly associated with an ordered downstream magnetic field and quasi-parallel shocks with strong turbulence, recent observations reveal a more nuanced picture. Some quasi-parallel shocks exhibit downstream rms magnetic fields that significantly exceed the mean field. These enhanced fluctuations are dominated by coherent rotations of the magnetic field vector, whose amplitude is much larger than that of the mean field. The rotations are well organized, forming distinct regions of strong and weak rotational activity. This demonstrates that downstream magnetic field fluctuations in quasi-parallel shocks need not be random and may instead reflect an underlying ordered structure.

How to cite: Golan, M. and Gedalin, M.: The rotational structure of downstream magnetic field  in quasi-parallel shocks, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4444, https://doi.org/10.5194/egusphere-egu26-4444, 2026.

Fast and slow solar wind exhibit distinct kinetic, compositional, and bulk properties that are related to their solar sources. In recent years, the Alfvénic slow wind has emerged as a third class of solar wind, characterized by speeds typical of nominal slow wind but by several properties commonly associated with fast wind. These include similarities in the solar source, often identified with regions of strongly diverging open magnetic field, challenging the traditional solar wind classification based solely on bulk speed.

The Solar Wind Analyzer (SWA) plasma suite onboard Solar Orbiter provides unique capabilities to investigate how Alfvénic slow wind differs from the fast wind and to relate these differences to their solar sources.

In this study, we present selected examples of Alfvénic solar wind streams observed by SWA. Combined observations from all SWA sensors, together with magnetic field measurements from the Magnetometer (MAG), are used to characterize plasma properties and solar wind fluctuations through spectral analysis. The magnetic connectivity of each stream to its solar source is investigated using Potential Field Source Surface (PFSS) extrapolations combined with ballistic backmapping from the spacecraft and supported by remote-sensing observations.

Our results show that proton velocity distribution functions exhibit anisotropies and field-aligned beams characteristic of Alfvénic streams, while electron pitch-angle distributions display clear strahl populations. Oxygen and carbon charge-state ratios are low in fast wind, while they are higher in Alfvénic slow wind, approaching values typical of standard slow wind. Magnetic connectivity indicates that fast wind originates from a large coronal hole, while Alfvénic slow wind intervals are connected to pseudostreamers with high expansion factors or to coronal holes whose field lines cross pseudostreamer regions that later dissipate.

These findings support the idea that a simple fast/slow wind classification is insufficient to link in situ solar wind properties to their solar sources, and suggest that Alfvénicity is closely related to source-region magnetic topology. In particular, super-radial expansion may play a role in reducing the wind speed while preserving Alfvénic characteristics, setting the conditions for the origin of the Alfvénic slow wind. These results also have implications for the energy balance of solar wind fluctuations observed in situ.

How to cite: D Amicis, R. and the List of authors: Characterization of Alfvénic Solar Wind Intervals Observed by SWA onboard Solar Orbiter, with Insights into Their Solar Sources, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9184, https://doi.org/10.5194/egusphere-egu26-9184, 2026.

SUNSTORM 1 was a 2-unit CubeSat that observed hundreds of solar flares from low Earth orbit during its three-year operation between August 2021 and September 2024. Its payload was the X-ray Flux Monitor for CubeSats (XFM-CS), a non-imaging X-ray spectrometer capable of observing flares from A to X level in the 1–30 keV range with high precision. First results have demonstrated the instrument’s suitability for studies of larger solar eruption events. 

We construct an overview of M and X class flares observed by SUNSTORM 1/XFM-CS during the mission. The soft X-ray flare spectra are fitted with a thermal model to obtain the peak flux, peak count, emission measure and flare temperature. For eruptive events, flare characteristics are connected to properties of the accompanying coronal mass ejections, and links between key parameters are discussed in relation to the underlying mechanisms. Our study highlights the scientific output of the SUNSTORM 1 mission and provides spectroscopic results of some of the biggest flares observed during the rise phase of Solar Cycle 25.

How to cite: Takala, S., Lehtolainen, A., Kilpua, E., Palmroth, M., and Huovelin, J.: Spectroscopic analysis of M and X class flares observed by SUNSTORM 1 XFM-CS, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9341, https://doi.org/10.5194/egusphere-egu26-9341, 2026.

Empirical relations are used to link modelled coronal magnetic field structure — particularly flux-tube expansion and distance to coronal hole boundary — to solar-wind speed. There is a lot of uncertainty embedded within these relations, particularly when used as an interface for heliospheric models. Hence, augmenting these relations could provide a powerful way to sample model uncertainty using ensemble techniques. We present a simplified empirical solar-wind speed equation that can be readily optimised for different configurations of an open-source Potential Field Source Surface and Schatten Current Sheet (PFSS+SCS) coronal model, in-lieu of the full Wang–Sheeley–Arge (WSA) equation. Optimisation is performed using a 10-year reanalysis dataset of in-situ solar-wind speed observations, reconstructed at 21.5 rS across longitudes at the sub-Earth point via a combined corotation and backmapping technique. We trial several functional forms for the simplified equation and explore three linear-regression techniques, highlighting the challenges of fitting empirical relations to noisy data. To minimise overfitting, we select a regression approach that fits directly to the distribution of reconstructed observations. We find an equation candidate that successfully reproduces the distribution of observed solar-wind speeds and performs comparably to WSA when coupled with the Heliospheric Upwind eXtrapolation with Time-dependence (HUXt) model to generate hindcasts at 1 AU. The new equation is not intended to replace WSA; the internal complexity remains a key element for WSA. Due to its simplicity, our equation produces less variability than WSA on average. The trade-off in complexity is balanced by usability within ensemble/multi-model frameworks. The equation can be easily perturbed to quantify uncertainty in windspeed magnitude and easily re-optimised for PFSS+SCS models with different source-surface and outer-boundary heights.

How to cite: Edward-Inatimi, N., Owens, M., Barnard, L., Lang, M., Turner, H., Gonzi, S., Marsh, M., and Yeates, A.: Adapted empirical modelling of near-Sun solar-wind speeds for use in ensemble forecasts, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12367, https://doi.org/10.5194/egusphere-egu26-12367, 2026.

Aims

We aim to investigate how the combined effects of spatial sparsity and temporal intermittency of stochastic heating events shape the stationary density and temperature profiles of the coronal plasma. We also aim to establish a theoretical kinetic framework capable of linking coronal heating with EUV observations.

Methods

We extend the kinetic model of Barbieri et al. (2025) by introducing a time-dependent stochastic boundary condition that accounts for intermittent heating at the chromospheric base. A surface coarse-graining procedure is applied to derive Vlasov-type equations for the averaged distribution functions. Analytical expressions are obtained for the corresponding density, temperature, and Differential Emission Measure (DEM) profiles, valid in the regime where the heating time scales are much shorter than the electron crossing time.

Results

We show that the temperature inversion and the coronal temperature plateau arise naturally when the combined parameter A = A_S × A_t is much smaller than unity, where A_S is the surface filling factor of heating events and A_t is their temporal duty cycle. Spatial and temporal intermittency are found to contribute in the same way to shaping the density and temperature profiles. The computed DEM exhibits a monotonic decrease with temperature up to 10⁶ K, followed by a peak marking the transition to the low corona, and shows good agreement with the observational results reported by Dolliou et al. (2024).

Conclusions

The present model unifies previous spatial and temporal kinetic descriptions of coronal heating within a single analytical framework. It provides a direct connection between the microscopic dynamics of stochastic heating and observable quantities such as the DEM.

How to cite: Barbieri, L. and Demoulin, P.: Coronal heating driven by spatially sparse and temporalintermittent energy release: a kinetic approach, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13483, https://doi.org/10.5194/egusphere-egu26-13483, 2026.

The energy source for major solar eruptions, such as flares and coronal mass ejections (CMEs), is  recognized to be the free magnetic energy (energy above the potential field state) stored in the solar magnetic field prior to eruption.  A key question for both predicting future eruptions and estimating their possible magnitude is, what is the bound to this energy?

The Aly-Sturrock theorem states that the energy of a fully force-free field cannot exceed the energy of the so-called open field. If the theorem holds, this places an upper limit on the amount of free energy that can be stored.  This is not a practical limit, as even the largest CMEs open only a portion of the coronal magnetic field.  The energy of a closely related field, the partially open field (POF), is believed to provide the corresponding limit for a localized region, such as an active region.  We have developed practical methods for estimating the POF energy (POFE). The estimates are based on potential-field like solves that can be computed rapidly.  We test our estimation methods by comparing them with the maximum energy storage achieved in MHD simulations of three solar eruptions:  July 14, 2000, October 1, 2011, and March 7, 2012.  We discuss the practicality of applying POFE estimates routinely to solar active regions. 

Research supported by NASA and NSF.

How to cite: Linker, J. A., Downs, C., Torok, T., Titov, V., and Caplan, R.: Energy Storage for Extreme Solar Eruptions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15303, https://doi.org/10.5194/egusphere-egu26-15303, 2026.

The presented work revisits the Statistical Injection of Condensed Helicity (STITCH) model by Antiochos et al. 2013; Mackay et al. 2014; Dahlin et al. 2022. The model includes a statistical description of the small-scale circulation motions in the solar photosphere and accounts for their effect on the magnetic helicity in the solar corona.

The statistical effect of small-scale circulation motions may be quantified following well-known analogy between the density of the magnetic moment of microscopic currents in magnetic media, on one hand, and the angular momentum density, on the other hand. Within the framework of magnetostatics the magnetic moment density of the microscopic currents (referred to as magnetization) is a statistical quantity characterizing the magnetized medium. Its gradient in non-uniform medium results in macroscopic magnetization current. Similarly, the angular momentum density may be involved as the statistical characteristic of the small-scale horizontal motions in the photosphere. In this application only the vertical component of the angular momentum density,  ζ, matters, which is ideologically close to the parameter used in the STITCH model.

Analogously to the magnetization current in magnetostatics, the horizontal gradient in ζ  would result in large-scale horizontal motion.  Indeed, for a uniform isotropic turbulence, the chaotic small-scale and high-frequency velocity would cancel in average. However, with any horizontal gradient in  ζ  the larger rotational velocity of a stronger nearby vortex is not fully balanced by the opposite rotation of a smaller vortex, thus resulting in the averaged larger-scale velocity.

This velocity is perpendicular to the horizontal gradient of vertical magnetic field, B_R or, equivalently, it is aligned with the level contours, B_R=const, of the vertical field. Such motion drags the footpoints of the field lines of the coronal magnetic field, thus resulting in generation and accumulation of the magnetic helicity. The average velocity field parameterized in terms of gradients in  ζ  may be used as the boundary condition for an analytical or numerical model of the solar corona. Particularly, it is implemented in the SWMF code of the University of Michigan and used to pump helicity and the magnetic free energy of the active region to bring it to the threshold of eruption

Assuming that the sign of  ζ   is the same as that of projection of the solar angular velocity vector on the radial direction, it should be mostly positive in the northern hemisphere and mostly negative in the southern hemisphere. The rate of magnetic helicity production appears to be proportional to the negative of  ζ.   Hence, the described mechanism may result in the magnetic helicity in the solar corona such that the negative magnetic helicity dominates in the northern hemisphere and the positive magnetic helicity dominates in the southern hemisphere. The latter conclusion agrees with the so called “hemisphere rule” as confirmed by statistical analysis of observations.

How to cite: Sokolov, I., Liu, X., Antiochos, S., and Gombosi, T.:  Non-Vanishing Angular Momentum Density in the Photospheric Horizontal Motions Induces Magnetic Helicity in the Solar Corona in Agreement with the “Hemisphere Rule”, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15456, https://doi.org/10.5194/egusphere-egu26-15456, 2026.

Rotation is an intrinsic property of stars and provides essential constraints on their structure, formation, evolution and interaction with the interplanetary environment. The Sun provides a unique opportunity to explore stellar rotation from the interior to its atmosphere in great detail. We know that the Sun rotates faster at the equator than at the poles, but how this differential rotation behaves at different atmospheric layers within it is not yet clear. Here we extract the rotation curves of different layers of the solar photosphere and chromosphere by using whole-disk Dopplergrams obtained by the Chinese Hα Solar Explorer (CHASE) for the wavebands Si I (6,560.58 Å), Hα (6,562.81 Å) and Fe I (6,569.21 Å) with a spectral resolution of 0.024 Å. We find that the Sun rotates progressively faster from the photosphere to the chromosphere. For example, at the equator, it increases from 2.81 ± 0.02 μrad s⁻¹ at the bottom of the photosphere to 3.08 ± 0.05 μrad s⁻¹ in the chromosphere. The ubiquitous small-scale magnetic fields and the height-dependent degree of their frozen-in effect with the solar atmosphere are plausible causes of the height-dependent rotation rate. The results have important implications for understanding solar subsurface processes and solar atmospheric dynamics.

How to cite: Rao, S.: Height-dependent differential rotation of the solar atmosphere detected by CHASE, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17757, https://doi.org/10.5194/egusphere-egu26-17757, 2026.

Compared to energetic electrons in solar flares, which can be readily observed in hard X-rays and radio, our understanding of energetic ions is severely deficient. Our main diagnostics for ions are gamma-ray observations, which remain challenging. A particularly intriguing case are behind-the-limb (BTL) gamma-ray flares, where the flare is occulted as seen from Earth, but nevertheless gamma-ray emission is detected by near-Earth spacecraft. Here, we investigate the relationship between the gamma-ray emission measured with Fermi-LAT, hard X-ray observations from STIX on Solar Orbiter, and ground-based radio observations, for a small sample of BTL gamma-ray flares. In all events, type II radio bursts were present that were synchronized in time with the gamma-ray emission. Conversely, we find a significant delay between the impulsive phase of the flare as recorded by STIX and the gamma-ray emission. These findings support the notion that the highly relativistic ions that produce the gamma-rays in BTL flares are accelerated at CME-driven propagating coronal shock waves rather than in large-scale flare loops.

How to cite: Warmuth, A.: New constraints on ion acceleration in behind-the-limb gamma-ray flares from Fermi-LAT, SolO/STIX, and ground-based radio observations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19231, https://doi.org/10.5194/egusphere-egu26-19231, 2026.

Coronal dimmings are observed as sudden and localized reductions in EUV and X-ray emission of the solar corona. Traditionally, significant dimmings at 1-2MK are regarded as robust indicators of coronal mass ejections (CMEs), reflecting the density depletion caused by plasma escaping into interplanetary space. Here we present a peculiar high-temperature dimming observed on 2012 July 5. Using Sun-as-a-star observations from SDO/EVE and GOES, we identified significant intensity drop in the Fe XVIII (6.5 MK) and Fe XX (9.3 MK) hot lines, with a maximum depth of over 20% observed in the GOES soft X-ray (SXR) flux. Spatially resolved analysis from SDO/AIA reveals that this signature originated from a failed eruption where the bulk of the plasma was constrained by the overlying magnetic loop system. This case demonstrates that deep coronal dimmings in hot lines can occur without actual mass loss, providing a critical caveat for the interpretation of stellar coronal dimmings used to find stellar CMEs.

How to cite: Wang, X., Chen, H., Veronig, A., and Tian, H.: A Long-term Coronal Dimming in High-Temperature Spectral Lines During an M-class Confined Flare, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19388, https://doi.org/10.5194/egusphere-egu26-19388, 2026.

Since December 2024, Parker Solar Probe has reached the mission's closest perihelion distance of 9.8 solar radii six times.  Data from each orbit has shown the spacecraft has been diving deep below the Sun's Alfvén surface with each pass, and covering nearly half the Sun at the same time. These measurements may therefore be interpreted as some of the most unambiguous direct sampling of a star's corona to date in regions which could previously only be probed with remote sensing techniques. In this talk we will review some recent insights into the large scale structure of the solar maximum corona and the Alfvén surface revealed by these new data, as well as our recent work studying the properties of polar-like fast solar wind in its early life and its subsequent evolution. We will close with a brief discussion on what we stand to learn with Parker continuing these deep dives as the Sun retreats into its next solar minimum.

How to cite: Badman, S.: The outer reaches of the Solar Corona as measured by Parker Solar Probe, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12552, https://doi.org/10.5194/egusphere-egu26-12552, 2026.

The properties of the solar wind, as measured in situ throughout the heliosphere, depend both on the characteristics of its coronal source and on the intrinsic processes governing its interplanetary evolution. Recently, radial and Parker spiral alignment techniques have been applied to Parker Solar Probe (PSP) and Solar Orbiter (SO) observations to investigate the radial evolution of the same solar wind parcel. These studies have shown that the solar wind can undergo significant acceleration even beyond its primary acceleration region (i.e., above 15 solar radii). However, such radial and Parker spiral alignments are rare in practice, which limits the statistical significance and general applicability of the results.We introduce a new source alignment technique designed to overcome these limitations. Using magnetic backmapping, we associate similar solar wind streams observed by the two spacecraft based on the proximity of their photospheric footpoints, combined with additional in situ stream similarity criteria. Applying the source alignment method to PSP and SO observations, we identify a total of 560 alignment intervals, each lasting 30 minutes. By constructing statistics over all alignments, we find that the solar wind speed increases by an average of 43\% (approximately 143 km/s) between the two probes. This result demonstrates that solar wind acceleration in the inner heliosphere remains significant compared to that occurring below 15 solar radii. Among the different energetic contributions, the radial evolution of the electron thermal energy shows the strongest correlation with the increase in kinetic energy. 

How to cite: Dakeyo, J.-B., Ervin, T., Bale, S., Démoulin, P., Sioulas, N., Réville, V., Liu, M., Rouillard, A., Maksimovic, M., Larson, D., Romeo, O., Louarn, P., and Livi, R.: On the Radial Evolution of the Solar Wind : The Source Alignment Method Applied to Parker Solar Probe and Solar Orbiter Observations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21926, https://doi.org/10.5194/egusphere-egu26-21926, 2026.

Solar energetic particles (SEPs) accelerated by distant interplanetary (IP) shocks driven by coronal mass ejections (CMEs) are different from energetic storm particles (ESPs), which are generally followed by geomagnetic storms. ESPs are believed to be accelerated by near-Earth IP shocks and often reach their peak intensities at the arrival times of these shocks at the Earth’s location or at the Sun–Earth L1 point. These energetic particles predominantly propagate along interplanetary magnetic field (IMF) lines. However, to the best our knowledge, the influence of IMF fluctuations on the directional anisotropy of energetic particle fluxes has not been investigated. In this study, we address this open question using directionally resolved energetic particle observations from the SupraThermal and Energetic Particle Spectrometer (STEPS) of the Aditya Solar wind Particle EXperiment (ASPEX) payload onboard Aditya-L1 mission. Following its launch on 02 September 2023, Aditya-L1 completed several Earth-bound orbits. During this phase, two of the six ASPEX-STEPS detector units were kept operational. We analyze energetic ion fluxes below 1.3 MeV obtained by these two detectors during a pair of SEP-ESP events observed by ASPEX-STEPS. Our results reveal that the temporal evolution of directional anisotropy in ion differential directional fluxes differs significantly between the SEP and ESP events. Furthermore, fluctuations in the directional anisotropy exhibit periodicities similar to those observed in IMF fluctuations, indicating a strong causal relationship. Number of common periodicities also differs between the SEP and ESP events. These findings are important to understand the transport of energetic particles and space weather impacts. The details of this study will be discussed.

How to cite: Dalal, B. and the ASPEX-Aditya L1 team: Directional anisotropy in solar energetic particle and energetic storm particle fluxes as measured by ASPEX-STEPS and the role of IMF fluctuations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16251, https://doi.org/10.5194/egusphere-egu26-16251, 2026.

Solar corona fills the whole solar system with the stream of ionized particles – solar wind. Its basic parameters and their evolution with the distance from the Sun were predicted by the Eugene Parker’s hydrodynamic theory in the middle of the last century but the latest observations covering the range from 0.09 to 100 AU give us the possibility to check and modify this crude simplification.

Two essential features distinguish the solar wind from a classical hydrodynamic flow - its weakly collisional nature and the presence of a magnetic field. The absence of frequent collisions allows a motion of different ion populations with various velocities and thus one should ask what a “real” solar wind velocity is. The magnetic field is not just passively frozen in the solar wind plasma as is often assumed, but its force action plays an important role in the release of the solar wind from the corona. Moreover, the magnetic field facilitates excitation and propagation of a variety of waves. The wave interactions lead to turbulence and form interplanetary shocks but their role in the solar-wind acceleration and heating is still not fully understood.

The lecture synthesizes multi-decade observations from numerous spacecraft to address these issues and to discuss their implications for solar-wind formation and evolution through heliosphere. Recent studies have revealed significant changes in the radial trends of plasma and magnetic-field parameters, including ion velocity (Nemecek et al. 2020), plasma beta (Safrankova et al. 2023), interplanetary shock properties and occurrence rates (Kruparova et al. 2025; Park et al. 2023), velocity-temperature relations (Durovcova et al. 2026), and the cross helicity of fluctuations (Park et al. 2025) in the region near Mercury’s orbit. We focus on the physical processes shaping this region and discuss possible interpretations of the observed phenomena. While solar-wind formation and evolution are currently the subject of intense investigation enabled by new observational capabilities, this lecture emphasizes our group's contributions to present knowledge.

How to cite: Nemecek, Z. and Safrankova, J.: Solar wind on the path from the Sun to Earth, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7940, https://doi.org/10.5194/egusphere-egu26-7940, 2026.