17th European Solar Physics Meeting ESPM-17

9 Sept 2024, 08:00 → 13 Sept 2024, 18:00 Europe/Rome

Turin, Italy

Alessandro Bemporad (Istituto Nazionale di Astrofisica (INAF)), Istvan Ballai (University of Sheffield)

(click here to download a higher resolution TIFF version)  

The European Solar Physics Meetings (ESPM) are organised every three years by the board of the European Solar Physics Division (ESPD), a joint division of the European Physical Society (EPS) and the European Astronomical Society (EAS). The meetings bring together a large number of scientists from Europe and beyond, who are active in the theoretical and observational study of solar phenomena.

The 17th European Solar Physics Meeting (ESPM-17) took place as a in-person meeting in the week of 9-13 September 2024, in the city of Turin, ITALY.

Important dates

• May 1st, 2024: Registration and abstract submission open.
• May 31st, 2024: Deadline for financial support applications.
• June 15th, 2024: Notification about final decision on financial support applications.
• June 30th July 12th, 2024: Deadline for early registration and abstract submission.
• August 15th, 2024: Final deadline for registration - in person attendance.
• August 31st, 2024: Final deadline for registration - remote attendance.
• 9-13 September, 2024: Meeting.

 

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In particular, ignore or flag anything claiming to be from hotel or travel agencies. Make sure to book your accommodation through recognised channels and not in response to emails with targetted offers, for example.

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Poster sessions ESPM-17 contributions - Poster session 1.pdf ESPM-17 contributions - Poster session 2.pdf

Tourist information NSL_ESPM17.pdf TORINO_city_and_its_area.pdf

Monday 9 September

Welcome and opening

Conveners: Dr Alessandro Bemporad (Istituto Nazionale di Astrofisica (INAF)), Dr Istvan Ballai (University of Sheffield)

ALTEC - Science Data Processing Centers in Turin.pdf

opening_presentation_IB.pptx

Thales Alenia Space_science products made in Turin.pdf

Welcome_slides_Bemporad.pptx

Solar interior, sub-surface flows and long-term variability

Convener: Dr Istvan Ballai (University of Sheffield)

1 Dynamo of the solar interior: Powering the decadal cycle and Its comparison to stellar magnetic cycles

The solar magnetism is generated and sustained through an internal dynamo. This process is driven by the combined action of two main mechanisms: turbulent convective motions and large-scale differential rotation (DR). The subsequent magnetic-field build-up can lead to intense surface eruptive events, but also sustain longer-term magnetic cyclic variabilities, such as the Sun's 11-year cycle. How is this magnetic activity powered? Evidence of magnetic cycles has also been reported on other solar-type stars, ranging from a few years to a few tens of years. How are these cycles controlled, and what can we learn from them?

In this talk, I will provide an overview of our current understanding of the dynamo operating within the solar convective envelope. I will especially focus on an extensive numerical study of the dynamo origins in solar-type stars, based on a series of 15 3D-MHD simulations, and illustrate what we can learn from this stellar context. In particular, this survey allows to propose a possible explanation for why the Sun possesses a long decadal cycle and to assess the power needed to maintain such magnetic activity. Finally, I will discuss how these models can be compared to current observations and further refined to improve our understanding of the solar dynamo.

Speaker: Dr Quentin Noraz (Rosseland Centre for Solar Physics, University of Oslo, Norway)

Topic1_Contr247_Noraz.pdf

2 The Sun’s differential rotation is controlled by baroclinically-unstable high-latitude inertial modes

Helioseismology has revealed that the Sun’s differential rotation profile substantially deviates from the well-known Taylor-Proudman theorem. It has been postulated that this deviation arises because the poles are warmer than the equator by a few degrees. Recently, global inertial modes of oscillation have been observed and identified on the Sun, including high-latitude modes with m=1,2,3. These high-latitude inertial modes are baroclinically unstable and thus quite sensitive to the latitudinal temperature difference inside the Sun. In this talk (based on Bekki, Cameron, & Gizon, Science Adv. 10:5643, 2024), we use 3D nonlinear numerical simulations to show that the pole-to-equator temperature difference in the Sun’s convection zone is limited to less than 7 K due to the nonlinear feedback of the high-latitude modes. It is also found that these inertial modes control the Sun's differential rotation by transporting heat equatorward and affecting the angular momentum balance. The observed amplitudes of these inertial modes indicate that the Sun's latitudinal differential rotation is near its maximum allowed value.

Speaker: Yuto Bekki (Max Planck Institute for Solar System Research)

Topic1_Contr262_Bekki.pdf

Topic1_Contr262_Bekki.pptx

3 EPS Invited Speaker - The role of convection during active region emergence

Abstract: The role of convection in forming active regions is controversial. In the thin-flux-tube model, the properties of the active regions are set by the flows in the flux tube during its rise: in the mean-field framework the properties are set by the interaction of the magnetic field with the surrounding turbulent convective motions. Recent observational results point to convection playing an important role in the formation and onset of Joy’s Law, challenging the thin flux-tube model. To understand how convective flows are involved in the formation of active regions, we aimed to identify where active regions emerge in the supergranulation flow pattern. We discovered that active regions preferentially emerge at specific locations within these flow patterns: the prograde ends of east-west aligned converging flow lanes. Preceding emergence by 0.5 to 1 day, these regions exhibit a net converging flow of 10-20 m/s, independent of magnetic flux, followed by an increase in outflows. Moreover, we propose that the Coriolis force acting on near-surface flows is responsible for Joy's Law, rather than deep-seated dynamics.

Speaker: Hannah Schunker (University of Newcastle)

Topic1_Contr345_Schunker.pptx

4 Modelling solar irradiances with proxies of activity along a cycle

There is a pressing need to model XUV solar irradiances, given the scarcity of current measurements. One of the measurable effects of a solar cycle is the significant (more than one order of magnitude) variation in XUV irradiance. XUV radiation drives the ionosphere and the thermosphere. As a first step in the modelling, we present EUV irradiances in a sample of strong spectral lines formed in different layers and regions of the solar atmosphere, obtained from the Solar Dynamics Observatory Extreme Ultraviolet Variability Experiment (SDO EVE) during 2010-2024 and the Solar and Heliospheric Observatory Coronal Diagnostic Spectrometer (SOHO CDS) covering the earlier maxima (1998-2014). We used the recently released version 8 EVE data. We present correlations with several proxies of solar activity, such as the Mg II index, sunspot numbers, and cm radio fluxes. Among these, the sunspot number proves to be the poorest proxy, whereas the Mg II index is a very good proxy for coronal lines (hotter temperature lines). We find a relatively strong linear relationship, which enables us to build a model essential for various applications. We find relatively good agreement between the SOHO CDS and SDO EVE irradiances for most of the stronger lines.

Speaker: Evangelia Deliporanidou (University of Cambridge)

ESPM_talk.pptx

Coffee break and poster session 1

Fundamental mechanisms of solar plasmas: magnetic reconnection, waves, radiation and particle acceleration

Convener: Dr Istvan Ballai (University of Sheffield)

5 Disentangling magnetic reconnection in the solar atmosphere.

In this presentation, we will explore the fundamental properties of magnetic reconnection, with a particular emphasis on the complexities of three-dimensional (3D) reconnection and the differences with two-dimensional (2D) scenarios. We will present recent state-of-the-art numerical simulations that show how 3D reconnection is key to understanding a variety of phenomena such as braiding, nanojets, and the heating of fundamental blocks in the atmosphere such as Coronal Bright Points, moreover including observations to support the theoretical findings. Additionally, we will address the implications of the differing Prandtl number in simulations versus the actual solar atmosphere. We will also discuss the challenges that need to be addressed in the near future both from theory and observations, and the potential opportunities from future missions such as MUSE and Solar-C.

Speaker: Daniel Nóbrega-Siverio (Instituto de Astrofísica de Canarias (IAC) | Rosseland Centre for Solar Physics (RoCS))

Topic2_Contr29_Nobrega-Siverio.key

6 Flux-rope mediated turbulent reconnection

Understanding the interplay between magnetic reconnection and turbulence is an important challenge in solar physics, which must be solved to address the fundamental processes and properties of solar flares and other coronal energy releases. In the last few years, exciting advances in this area have been enabled by 3D direct numerical simulations that capture the generation of turbulence inside the reconnection layer. Interestingly, these simulations exhibit features associated with the Lazarian-Vishniac model of 3D turbulent reconnection (turbulence and field line dispersion) and features associated with 2D plasmoid mediated reconnection (flux ropes and a reconnection rate of 0.01 in MHD and 0.1 with collisionless physics). This talk presents a new theoretical model that reconciles aspects of turbulent and plasmoid-mediated reconnection, differing from the Lazarian-Vishniac theory by emphasizing the roles of locally coherent magnetic structures and magnetic helicity, and formally extending the plasmoid-mediated mechanism to 3D. The new conceptual model successfully describes the main features of MHD and PIC simulations of self-generated turbulent reconnection, including the magnetic field structure and reconnection rate.

Speaker: Alexander Russell (University of St Andrews)

Topic2_Contri230_Russell.pptx

7 State-of-the-art observational aspects of MHD waves in the lower atmosphere

MHD waves are recognized as significant contributors to the energy budget of the solar atmosphere, the acceleration of the solar wind and the composition of coronal plasma. Recent advancements in instrumentation, techniques, and processing methods have unlocked new diagnostic capabilities for exploring the excitation and propagation of MHD waves within various magnetic structures in the solar atmosphere. In this contribution a broad state-of-the-art overview of recent advancements in the identification, characterization and analysis of oscillations observed in diverse magnetic configurations in the lower solar atmosphere will be provided. Special attention will be given to the perspectives that upcoming instruments will introduce to the field.

Speaker: Marco Stangalini (ASI Italian Space Agency)

Fundamental mechanisms of solar plasmas_Stangalini.pptx

8 Simulating Energetic Particle Transport in the Solar Corona with COCONUT+PARADISE

Solar eruptive events such as coronal mass ejections (CMEs), along with the associated solar energetic particles (SEPs), pose serious threats to spacecraft and astronauts. The growing impact of these harsh space weather events on modern societies has driven the development of numerical models capable of enhancing our understanding of the underlying physics and reliably forecasting these events. A recent example is the particle transport code PARADISE, which is coupled to heliospheric magnetohydrodynamic (MHD) models such as EUHFORIA and Icarus, and is used to model the acceleration and transport of SEPs at radial distances r > 0.1 au.

However, since the evolution of CMEs as well as the acceleration and transport of SEPs occur already deep in the corona (r < 0.1 au), we introduce the novel COCONUT+PARADISE model to address this issue. The data-driven, global coronal MHD model COCONUT, part of the COOLFLuiD platform, uses synoptic magnetograms for the inner boundary conditions and solves the three-dimensional ideal MHD equations to derive coronal background configurations from 1 up to 25 solar radii. To model CMEs in COCONUT, the unstable modified Titov-Démoulin flux rope model is utilised. Subsequently, PARADISE uses these coronal configurations to evolve energetic particles through these backgrounds by solving the focused transport equation (FTE) using a Monte-Carlo approach. We present simulation results that illustrate the propagation of SEPs within the solar atmosphere. Furthermore, we highlight the potential of our model for future work encompassing the study of particle transport from the base of the corona to Earth and beyond.

Speaker: Edin Husidic (KU Leuven, Belgium/University of Turku, Finland)

ESPM17_slides_edin_husidic.pptx

Lunch break

Fundamental mechanisms of solar plasmas: magnetic reconnection, waves, radiation and particle acceleration

Convener: Daniel Müller (ESA)

9 Radiation Properties of Cool Coronal Condensations

Cool plasma condensations in the corona manifest themselves as various types of
prominences, loop structures, flare loops, coronal rain etc. They can be highly
dynamical, exhibiting fine structures down to resolution of current instruments.
Nowadays they are modeled using multidimensional MHD simulations. But to compare
with observations, a non-LTE radiative-transfer spectral synthesis is needed.
We will review current approaches to synthesize the spectra and monochromatic
images from up-to-date MHD models. The methods are based on multispecies-multilevel
non-LTE modeling which provides the overall excitation-ionization structure.
An important ingredient is the illumination from the surrounding solar atmosphere.
As a result one can determine the partial ionization of the plasma and optically-thick
radiative losses through the whole volume, both being critical for realistic
MHD simulations. We will review the modern approaches and discuss future prospects.

Speaker: Petr Heinzel (Czech Academy of Sciences)

CoCoCo.pptx

10 Nanoflare and nanojets in MHD simulations of magnetic reconnection in coronal loops.

Reconnection events in coronal loops are singularly too small and fast to be detected (nanoflares), whereas their collective action could be sufficient to sustain the million degrees corona against thermal conduction and radiative losses. Recent studies have observed and modelled the dynamic counter part of nanoflares, i.e. the nanojets, which are a byproduct of the magnetic reconnection and this avenue seems a viable one to crack the nanoflares enigma. It remains to understand if there is a simple relationship between the properties of the nanoflare and the nanojet, so to explain in which cases the latter, when observed, could give away the occurrence of the former. We will analyse the physics of either phenomena to illustrate the detailed mechanism and key aspects which future studies should pay attention to. Moreover, in order to study the nanoflare population, we need to detect and isolate nanojets even when several take place one after the other. In MHD simulations, a number of detection techniques can be developed in increasingly more complex scenarios from the simple tangling of magnetic field lines to kink instabilities and cascade reconnection. These 3D MHD simulations are key to bridge the gap between idealised magnetic reconnection models and future spectroscopic observations (MUSE) providing key indications on what observations can be planned to export this approach from MHD simulations to observations.

Speaker: Paolo Pagano (Università degli Studi di Palermo)

Topic2_Contr128_Pagano.pptx

11 Estimating the total energy content in escaping accelerated solar electron beams

Quantifying the energy content of accelerated electron beams during solar eruptive events is a key outstanding objective that must be constrained to refine particle acceleration models and understand the electron component of space weather. Previous estimations have used in situ measurements near the Earth, and consequently suffer from electron beam propagation effects. In this study, we deduce properties of a rapid sequence of escaping electron beams that were accelerated during a solar flare on 22 May 2013 and produced type III radio bursts, including the first estimate of energy density from remote sensing observations. We use extreme-ultraviolet observations to infer the magnetic structure of the source active region NOAA 11745, and Nançay Radioheliograph imaging spectroscopy to estimate the speed and origin of the escaping electron beams. Using the observationally deduced electron beam properties from the type III bursts and co-temporal hard X-rays, we simulate electron beam properties to estimate the electron number density and energy in the acceleration region. We find an electron density (above 30 keV) in the acceleration region of 10^3 cm^-3 and an energy density of 5.74x10^-5 erg cm^-1. Radio observations suggest the particles travelled a very short distance before they began to produce radio emission, implying a radially narrow acceleration region. A short but plausibly wide slab-like acceleration volume of 10^26-10^28 cm^3 atop the flaring loop arcade could contain a total energy of 10^24-10^25 erg (~100 beams), which is comparable to energy estimates from previous studies.

Speaker: Dr Alexander James (University College London)

20240909_ESPM_AJames.pdf

12 The angular dependence of rise and decay times of solar radio bursts using multi-spacecraft observations

Radio photons interact with anisotropic density fluctuations in the heliosphere which can alter their trajectory and distort the properties that are deduced from observations. This is particularly evident in solar radio observations, where anisotropic scattering leads to highly-directional radio emissions, meaning that observers at varying locations will measure different radio-source properties. However, it is not known whether the measurements of the decay time of solar radio bursts also depend on the observer’s position. Decay times are dominated by scattering effects, and so are frequently used as proxies of the level of density fluctuations in the heliosphere, making the identification of any location-related dependence crucial. We combine multi-vantage observations of interplanetary Type III bursts from four non-collinear, angularly-separated spacecraft with simulations to investigate the dependence of the decay- and rise-time measurements on the separation of the observer from the source. We propose a function to characterise the entire time profile of radio signals, allowing for improved spectroscopic estimations, while demonstrating that the rise phase of radio bursts is non-exponential, having a non-constant growth rate. We determine that the decay and rise times are independent of the observer's position, identifying them as the only properties that do not require corrections for the observer's location. Moreover, we examine the rise-to-decay time ratio and find that it does not depend on the frequency. Therefore, we provide the first evidence that the rise phase is also significantly impacted by scattering effects, adding to our understanding of the plasma emission process.

Speaker: Dr Nicolina Chrysaphi (LPP, Sorbonne University, France)

Chrysaphi_ESPM2024_slides.pptx

13 Simulation of particle acceleration and transport in 3D turbulent reconnection regions

Observation and simulation studies suggest that particles can be accelerated in the current sheet and above the loop-top during solar flares. Considering the flare process is a turbulent 3D phenomenon in reality, 3D models are crucial for understanding and interpreting particle acceleration in flares. Using the Stochastic Differential Equations (SDE) method to solve the Parker Transport Equation, we investigate electron acceleration in the current sheet and above the loop-top in a 3D simulation. We find that in the classical 2D model, in non-classical configurations, the shock distribution can also accelerate particles. However, in the 3D simulations, particles can still be accelerated to hundreds of keV but the particle acceleration capability is significantly reduced. After turbulence appears at the loop-top, the fragmented TS can still accelerate particles without the need for a stable TS as in the classical model. Additionally, we observe particle acceleration in the current sheet. These findings are significant for our understanding of particle acceleration in solar flares.

Speaker: Xin Cheng (Nanjing University)

Topic2_Contr184_Ren.pptx

Coffee break and poster session 1

Energy and mass transfer throughout the solar atmosphere and structures within

Convener: Stanislav Gunár (Astronomical Institute of the Czech Academy of Sciences)

14 Restructuring of magnetic fields at the periphery of granules

Plasma flows in the near-surface region are thought to play an important role in replenishing the quiet Sun magnetic field. The interaction of magnetic fields with the complex flow structure causes these fields to reorganize at sub-granular scales. Horizontally aligned vortex flows near the edge of solar granules can grab magnetic fields from beneath and bring them to the visible surface. However, it is still unclear if these magnetic fields are amplified during their motion through such a turbulent environment. Here, we present results from a recent high-resolution radiative magnetohydrodynamic simulation carried out using the CO5BOLD code, focusing specifically on the periphery of granules. We investigate the formation and evolution of coherent vortex structures in these regions to determine if they contribute to amplifying the magnetic field to levels observable on the quiet Sun.

Speaker: G. Vigeesh

15 Vortex Flows in the Solar Atmosphere: Detection and Heating Mechanisms in 3D MHD Numerical Simulations

Vortex flows are structures associated with the rotation of the plasma and/or the magnetic field that are present throughout the solar atmosphere, which have been detected in both numerical simulations and observations. In recent years, their study has become increasingly important, as they are present on a wide variety of temporal and spatial scales and can connect several layers of the solar atmosphere. In this way, it has been proposed as one of the possible mechanisms responsible for the energy transport and heating of the chromosphere and solar corona.

In this work we performed an automatic detection of these structures in 3D MHD numerical simulations using the MANCHA3D code. The code incorporate non-ideal MHD effects and simulations are available in three magnetic fields configurations at different spatial resolutions. To detect vortex structures we proposed to use the novel SWIRL code (Canivete Cuissa & Steiner (2022)), which combines mathematical criteria based on the velocity gradient tensor to identify such structures with an advanced clustering algorithm. By applying this code, we have been able to determine multiple structures associated with small and large scale vortices that extend in height in our simulations. Prior to the detection, simulations have been filtered in order to remove the continuous oscillation caused by the presence of p-modes. We focus our study on the temperature distribution and heating mechanisms (ambipolar diffusion and viscous and ohmic dissipation) that take place in the detected vortices, and how they change as the magnetic field and spatial resolution are modified.

Speaker: Matias Koll Pistarini (Instituto de Astrofísica de Canarias)

Topic3_Contr133_Koll_Pistarini.pptx

16 High flow speeds and transition-region like temperatures in the chromosphere caused by reconnection

Flux emergence in the solar atmosphere is a complex process that causes release of magnetic energy as heat and acceleration of solar plasma. We analyse imaging spectropolarimetric data taken in the He I 1083 nm line at a spatial resolution of 0.26", a time cadence of 2.8 s, and a spectral range of 150 km s$^{−1}$ around the line. This data is complemented by imaging spectropolarimetric data in the Ca II K, Fe I 617.3 nm, and Ca ii 854.2 nm lines. We compute He I 1083 nm profiles from a radiation-MHD simulation of the solar atmosphere to help interpret the observations.
We find fast-evolving blob-like emission features in the He I 1083 nm line at locations where the magnetic field is rapidly changing direction, and these are likely sites of magnetic reconnection. We fit the lines with a model consisting of an emitting layer located below a cold layer representing the fibril canopy. Numerical modeling provides evidence that this model, while simple, catches the essential characteristics of the line formation. The morpholoigy of the emission in He I 1083 nm is localized and blob-like, unlike the emission in the Ca II K line, which is more filamentary.
Based on the high temperatures needed for He I 1083 nm emission, the high Doppler speeds in the emission features, and their blob-like appearance, we conclude that at least a fraction of them are produced by plasmoids that occur during magnetic reconnection.

Speaker: Jorrit Leenaarts

Topic3_Contr93_leenaarts.pptx

17 On the sunspot penumbra formation with nonlinear force-free field extrapolations

The mechanism behind the formation of the solar penumbra remains a topic of debate, with the magnetic field configuration above the photosphere not yet thoroughly explored. In this study, we examine the formation of sunspot penumbra through a novel approach using the analysis of magnetic fields derived from Non-Linear Force-Free Field (NLFFF) extrapolations. We perform NLFFF extrapolations on HMI/SDO data, capturing the evolution of active region NOAA 12757 before, during, and after penumbra formation. By tracking the magnetic field lines, we present unprecedented insights into the changes in topology and connectivity. Initially, prior to penumbra formation, we observe low-lying sea-serpent magnetic fields that gradually rise and become more vertical. The penumbra forms during this transition, and its extent stabilizes once the rise of the low-lying sea-serpent magnetic field lines ceases.

Speaker: Jan Jurcak (Astronomical Institute of the Czech Academy of Sciences)

Topic3_Contr67_Jurcak.pptx

18 Impact of small-scale photospheric magnetic reconnection events on the upper atmosphere

Ellerman bombs are sites of magnetic reconnection in the deep solar atmosphere. They can be observed as strong enhancements of the hydrogen Balmer lines and display rapid variability on small spatial and temporal scales. They are typically found in young active regions with vigorous emergence of magnetic fields. High-spatial resolution observations with the Swedish 1-m Solar Telescope in La Palma showed that Ellerman bombs can be also be found in large numbers in the quiet Sun. These quiet Sun Ellerman bombs are typically smaller and shorter lived than their active region counterparts. A recent study in the Balmer H-epsilon line showed that the quiet Sun may host more than 750,000 Ellerman bombs at any time. We analysed co-temporal SST and IRIS observations and found that a number of the longer lived quiet Sun Ellerman bombs can be associated with signal in the IRIS transition region SJI 1400Å and Si IV spectral lines. In another study, we found a number of examples that suggest a connection between quiet Sun Ellerman bomb events and spicule activity. This suggest that at least some spicules are driven by magnetic reconnection in the deep atmosphere.

Speaker: Luc Rouppe van der Voort (Rosseland Centre for Solar Physics, University of Oslo)

Topic3_Contr206_Rouppe.pdf

Topic3_Contr206_Rouppe.pptx

Tuesday 10 September

Energy and mass transfer throughout the solar atmosphere and structures within

Convener: Stanislav Gunár (Astronomical Institute of the Czech Academy of Sciences)

19 Small EUV brightenings in the quiet solar atmosphere: new insights from the Solar Orbiter mission

Small scales EUV brightening in the solar atmosphere are observed everywhere and they have been classified following a variety of observational properties. For instance, they resemble small jets, bright dots or tiny loops. X-ray and EUV observations from the existing imagers, have been used to infer, for instance, the energy budget needed to heat the solar corona, as we expect the heating happening at small and impulsive way. EUV small scales brightenings have also been investigated as possible locations where the nascent solar wind escapes from the solar surface, as the result of small scale interchange-reconnections. These investigations have, however, not provided conclusive observational proofs to these phenomena.
The Solar Orbiter mission, launched in 2020, is providing opportunities for new insight into these problems, as it carries high temporal and spatial resolutions instruments accessing yet unresolved scales. In particular, EUI/HRIEUV telescope has revealed the existence of EUV brightenings down to the spatial resolution of 200 km and few seconds of lifetime, so extending our knowledge of these features to smaller scales. Their link to the photosphere is studied with the telescope PHI, which attains similar spatial resolutions.
In this talk, I will present and discuss these new observations. I will put them in the context of the present knowledge of the small scale EUV dynamical events, and I will discuss their possible link with the deepest regions of the solar atmosphere.

Speaker: Susanna Parenti (Institut d'Astrophysique Spatiale, CNRS/Université Paris-Saclay)

20 First Solar Orbiter observation of a Dark Halo in the solar atmosphere

Dark halos (DHs) are regions of reduced emission compared to the quiet Sun that are observed around active regions (ARs) at various wavelengths and wavebands, corresponding to chromosphere, transition region (TR) and corona. While in the chromosphere DHs are associated with the H$\alpha$ fibril vortex around the AR cores, in the upper atmospheric layers the origin of their dark emission is still unknown. Because of their different spatial appearances, it is not even clear if the DHs observed at the different layers are related to each other. In this work we present the first Solar Orbiter’s observation of a DH in the solar atmosphere which includes EUI, SPICE and PHI data taken on the 19 March 2022, when Solar Orbiter was approaching its fourth perihelion. We take advantage of Solar Orbiter’s proximity to the Sun to study the temporal evolution of the 174 Å DH’s fine structure with unprecedented spatial resolution. We also show cospatial and cotemporal intensity maps of SPICE’s cooler spectral lines to reveal the DH’s response to TR temperature increase. Finally, we spatially correlate the DH observed with EUI and SPICE to the PHI’s BLOS magnetogram in order to shed light on the dark nature of DHs.

Speaker: Serena Maria Lezzi (Istituto Nazionale di Astrofisica (INAF))

FirstSOobsDarkHalo_105_SerenaMariaLezzi.pptx

21 Stereoscopic study of energy and mass transfer in the solar atmosphere

We present the results of coordinated observations of the Swedish 1-m Solar Telescope with Solar Orbiter that took place from October 12th to 26th 2023. The campaign resulted in 7 datasets of various quality. The observational programs were adjusted to the seeing conditions. The observations cover two active regions, a sunspot and a coronal hole. We focus on the morphology and evolution of several targets that are observed from two vantage points. We decipher the findings with numerical simulations.

Speaker: Sanja Danilovic (Stockholm University)

topic2_cotr279_danilovic.pptx

22 Waves in coronal structures up to 1 Rsun?

At Solar Orbiter’s perihelion, the FSI telescope of the EUI instrument images the EUV corona up to 1 Rsun above the limb with a plate-scale better than 1000 km on the Sun. Here we report on exceptional FSI image sequences in the 17.4nm bandpass with deep exposures and a 30s cadence during the so-called “Density Fluctuations” and “Probe Quadrature” Solar Orbiter Observing Plans (SOOPs).

These data, with unique high S/N in the high EUV corona, reveal ubiquitous intensity fluctuations propagating outward along open magnetic field-lines up to 1 Rsun above the limb, well beyond the FOV of traditional EUV imagers. Difference movies suggest these propagating intensity fluctuations have both a longitudinal as well as a transversal “swaying” component.

We will discuss the relation of these high-altitude fluctuations with similar features reported before in the low solar corona (eg COMP & AIA data), as well as higher up in simultaneous Metis data. Implications for the energisation of the solar wind will be discussed.

Speaker: David Berghmans (Royal Observatory of Belgium)

23 Probing the physical parameters of the solar chromosphere and the corona through radio observations in the 18-26 GHz frequency range

The radio Sun in the centimetric range (18-26 GHz) is dominated by the quiet-Sun emission, which covers the entire surface of the solar disk as a mostly uniform background. The quiet-Sun is mostly characterised by bremsstrahlung (free-free) emission at local thermal equilibrium. The solar disk at these frequencies shows dynamical chromospheric structures and phenomena -- such as Active Regions, Coronal Holes, Polar Brightening, and Flares -- whose emission generally takes place by the interaction between the solar matter and the variable local magnetic fields. This kind of radiation provides gyro-magnetic component, in addition to the free-free component typical of the quiet-Sun.

Using about 450 radio solar maps obtained in the context of the SunDish project -- devoted since 2018 to the radio imaging and monitoring of the Sun and its atmosphere through the large single-dish radio telescopes of the Italian National Institute for Astrophysics (INAF) -- we present the phenomenology of the chromosphere in the radio K-band (18-26 GHz), still characterised today by poor observing coverage. The low noise, the accurate absolute calibration, and the great sensitivity of INAF radio telescopes make these data crucial to probe the physical parameters of the chromosphere and corona in terms of solar size, density, temperature, and magnetic fields. We also describe the instruments and scientific tools that allow us to study the physics of these solar atmospheric layers, developed for our early scientific works and future developments in the context of the SunDish project.

Speaker: Dr Marco Marongiu (Istituto Nazionale di Astrofisica (INAF))

Topic3_Contr101_Marongiu.pptx

Coffee break and poster session 1

Energy and mass transfer throughout the solar atmosphere and structures within

Convener: Dr Sven Wedemeyer (Rosseland Centre for Solar Physics, University of Oslo, Norway)

24 Thermal non-equilibrium : its importance for the energy and mass cycles in the atmosphere and its possible solar wind implications

Thermal non-equilibrium (TNE) is a thermodynamical state set by a stratified (mainly at the footpoints) and quasi-steady heating. It is believed to play a major role in producing a variety of very common solar phenomena, in particular: prominences, coronal rain, and long-period EUV pulsations. These two later phenomena are the two faces of the same coin: the EUV pulsations results of the temperature and density variations in the cooling phases of TNE cycles, while coronal rain is produced by a thermal instability leading to the dramatic condensation of the plasma in the final phases of these cycles.

I will review the current state of knowledge about TNE, the latest developments on TNE observations and modeling in the solar atmosphere, and the remaining puzzles on the topic.
In particular, its recent detection in open-closed topologies lead to many questions on the interplay of TNE with interchange reconnection at coronal null-points and draw interesting perspectives on linking mass and energy transport in the solar atmosphere to solar wind release mechanisms.
Finally, I will talk about future observations with Solar Orbiter and upcoming missions such as MUSE and Solar-C.

Speaker: Dr Clara Froment (CNRS/LPC2E)

Topic3_Contr281_Froment.pptx

25 Numerical Modeling of Prominence Dynamics, Eruption and Coronal Waves Propagation Using MPI-AMRVAC

Solar prominences are the birthplaces of coronal mass ejections, making studies of their pre-eruptive dynamics crucial for space weather. In this talk, I will review our most recent numerical studies of prominence dynamics with MPI-AMRVAC code.
Our investigation extends to the eruption evolution and the generation of coronal waves, which propagate over considerable distances through a magnetized medium and interact with flux rope prominence. This study relies on a numerical experiment performed with the MPI-AMRVAC code, using a gravitationally stratified corona and accounting for nonadiabatic effects. The initial magnetic field configuration consists of a dipole and a pre-existing flux rope in the low corona that suddenly erupts due to a 2.5D catastrophe.
The eruption gives rise to multiple energetic waves propagating throughout the magnetized corona. These waves ultimately reach distant prominences, evidently perturbing it. We generated synthetic images to increase our findings' comparability with SDO/AIA observations of similar events.
We analyzed and compared two scenarios with and without a uniform background magnetic field component aligned with the invariant direction. These scenarios result in different beta regimes and overall distinct evolutions of the eruption, variations in tearing instability within the current sheet, and differences in the propagation of coronal waves.

Speaker: Dr Valeriia Liakh (Centre for mathematical Plasma Astrophysics KU Leuven)

ESPM17_September_10th.pptx

26 On the magnetic source of chromospheric heating

It is generally believed that the chromosphere is heated by the dissipation of acoustic waves or predominantly acoustic slow modes. Here we propose that some of these essentially acoustic waves have a magnetic origin in that they are generated by torsional Alfénic pulses propagating along small-scale magnetic flux concentrations that root in the photosphere. But how do these torsional Alfvén waves dissipate? Recent observations with the Daniel K. Inouye Solar Telescope (DKIST) by C.E. Fischer et al. reveal propagating, arc-shaped bright fronts emanating from chromospheric bright grains. These are located above corresponding photospheric bright points, which in turn are found to interact with vortical flows prior to the appearance of the chromospheric bright fronts. Corresponding three-dimensional magnetohydrodynamic simulations reveal that the arc-shaped structures are weak shock fronts triggered by the torsional Alfvénic pulse of the underlying magnetic flux concentration. Here, we propose a mechanism by which the torsional Alfvén wave excites a predominantly acoustic weak shock front capable of dissipating the torsional Alfvén wave.

Speaker: Oskar Steiner (Leibniz-Institut für Sonnenphysik)

Topic3_Contr229_Steiner.pptx

27 Plasma Motions and Compressive Wave Energetics in the Solar Corona and Solar Wind from Radio Wave Scattering Observations

Radio signals propagating via the solar corona and solar wind are significantly affected by compressive waves, impacting solar burst properties as well as sources viewed through the turbulent atmosphere. While static fluctuations scatter radio waves elastically, moving, turbulent or oscillating density irregularities act to broaden the frequency of the scattered waves. Using a new anisotropic density fluctuation model from the kinetic scattering theory for solar radio bursts, we deduce the plasma velocities required to explain observations of spacecraft signal frequency broadening. The frequency broadening is consistent with motions that are dominated by the solar wind at distances $\gtrsim 10$ $R_\odot$, but the levels of frequency broadening for $\lesssim 10$ $R_\odot$ require additional radial speeds $\sim (100-300)$ km s$^{-1}$ and/or transverse speeds $\sim (20-70)$ km s$^{-1}$. The inferred radial velocities appear consistent with the sound or proton thermal speeds, while the speeds perpendicular to the radial direction are consistent with non-thermal motions measured via coronal Doppler-line broadening, interpreted as Alfvénic fluctuations. Landau damping of parallel propagating ion-sound (slow MHD) waves allow an estimate of the proton heating rate. The energy deposition rates due to ion-sound wave damping peak at a heliocentric distance of $\sim(1-3)$ $R_\odot$ are comparable to the rates available from a turbulent cascade of Alfvénic waves at large scales, suggesting a coherent picture of energy transfer, via the cascade or/and parametric decay of Alfvén waves to the small scales where heating takes place.

Speaker: Francesco Azzollini (University of Glasgow)

28 Global coronal models driven with Alfven and kink waves

In recent years, the so-called AWSOM models are a new generation of solar atmospheric models, which incorporate the heating and forces of Alfvén waves on top of more classical effects. They are outperforming older models capturing most aspects of the solar corona, but are still lacking in open field regions because of the lack of reflections and turbulence development.
In this contribution, I will highlight our development of a new formalism that allows to describe the kink wave on coronal plumes and loops in a similar way as the Alfvén waves in the AWSOM models. In this new development, we generalise the Elsässer variables to Q-variables in order to follow waves that are not Alfvén waves. In the talk, I will explain the governing equations, highlight early outcomes of the proof-of-concept in 1D configurations, where I show that kink wave driving leads to additional coronal heating.

Speaker: Tom Van Doorsselaere (KU Leuven)

dens_orange.avi

Topic3_Contr103_VanDoorsselaere.pdf

Waves in a coronal hole.mp4

Lunch break

ESPD Business Meeting

Candidates ESPD Board.pdf

Energy and mass transfer throughout the solar atmosphere and structures within

Convener: Dr Sven Wedemeyer (Rosseland Centre for Solar Physics, University of Oslo, Norway)

29 Are Switchbacks the Magnetohydrodynamic Equivalent of Smoke Rings?

Switchbacks are large Alfvénic deflections , or even reversals, of the magnetic field in the solar wind. Many authors have suggested that switchbacks are linked to interchange reconnection in the solar corona, but the manner of this connection remains unclear. In our previous work we have shown that both the interchange reconnection process itself (Wyper et al. 22) as well as coronal jets and jetlets that involve interchange reconnection (Wyper et al. 18, Pariat et al. 09) launch Torsional Alfvén waves into the solar wind. Furthermore, photospheric swirls are also thought to be an abundant source of coronal Torsional Alfvén waves.

Here we present a new study of how such Torsional Alfvén waves can evolve into switchbacks in an super-radially expanding solar wind. We find that through a combination of length contraction due to the reduction in Alfvén speed with height, and the onset of a Rayleigh-Taylor-like instability the waves evolve into a vortex ring configuration involving Alfvénic radial field reversals. We show that this evolution is relatively insensitive to the injection time or driving speed, provided a sufficient amount of twist is injected overall. We also find that the switchbacks within the vortex rings have a preferential deflection near helmet streamers that may explain observed RTN deflection biases. Overall, our findings support the idea that Torsional Alfvén waves launched into the solar corona can provide seed perturbations for the formation of switchback radial field reversals within the solar wind.

Speaker: Peter Wyper

Topic3Contri11Wyper.pptx

30 Photospheric driving of sustained kink oscillations in coronal loops

Sustained kink oscillations in coronal loops have long been observed in TRACE, SDO/AIA, and more recently in SolO/EUI images. Although their properties are quite well-known now, their driver and excitation mechanism remain under active debate. In this contribution I give an overview over recent publications and discuss how the different proposed ideas/theories for photospheric driving can be reconciled with each other and with observations. A 3-D radiative MHD simulation using the Bifrost code (Kohutova et al. 2021, 2023) is explored to get first insights. We then exploit high-resolution coronal and photospheric observations taken recently by SolO/EUI/HRI and the Swedish 1-m Solar Telescope (SST) respectively during a dedicated coordinated campaign run in October 2023. This study provides actual numbers to quantify the driving of coronal loop footpoints that is derived from horizontal flows observed in the photosphere by SST. An attempt is then made to link the driver parameters with the properties of sustained kink oscillations detected in EUI/HRI. This work has been funded by the Research council of Norway (grant 324523).

Speaker: Nicolas Poirier (IRAP)

Topic3_Contr132_Poirier.pptx

31 Mass Cycle and Dynamics of a Virtual Quiescent Prominence

The mass cycle of solar prominences or filaments is still not completely understood. Researchers agree that these dense structures form by coronal in-situ condensations and plasma siphoning from the underlying chromosphere. In the evaporation-condensation model siphoning arises due to evaporation of chromospheric plasma from localised footpoint heating but this is challenging to justify observationally. Here, we simulate the reconnection-condensation model at extreme-resolutions down to 20.8 km within a three-dimensional magnetohydrodynamic coronal volume. We form a draining, quiescent prominence and associated coronal rain simultaneously. We show that thermal instability – acting as a trigger for local condensation formation – by itself drives siphoning flows from the low-corona without the need of any localised heating. In addition, for the first time we demonstrate through a statistical analysis along more than 1000 magnetic field lines that cold condensations give rise to siphoning flows within magnetic threads. This siphoning arises from the strong pressure gradient along field lines induced by thermal instability. No correlation is found between siphoning flows and the prominence mass, making thermal instability the main in-situ mass collection mechanism. Our simulated prominence drains by gliding along strongly sheared, asymmetric, dipped magnetic arcades, and develops natural vertical fine-structure in an otherwise horizontal magnetic field due to the magnetic Rayleigh-Taylor instability.By synthesising our data, our model shows remarkable agreement with observations of quiescent prominences such as its dark coronal cavity in extreme-ultraviolet emission channels, fine-scale vertical structure and reconnection outflows which, for the first time, have been self-consistently obtained as the prominence evolves.

Speaker: Dion Donné (KU Leuven)

Topic3_Contr30_Donné.pptx

32 Simulation of a solar prominence with MURaM

Solar prominences are cool and dense plasma clouds suspended in the hot solar corona, supported by the magnetic field. They are common features in the solar atmosphere, but their exact formation mechanism is still unclear. We use the radiative magnetohydrodynamic code MURaM to simulate the formation and dynamics of a prominence in the solar atmosphere. MURaM includes the relevant physical processes to simulate the solar photosphere, chromosphere and corona.
We create a stable, dipped magnetic arcade configuration in a 3D simulation box and let it evolve. In the course of the simulation, a solar prominence forms self-consistently. First, a dense plasma seed ejected from the chromosphere randomly settles into a magnetic dip of the field configuration and gets cooled by radiative losses. The resulting pressure drop then drives a strong inflow of hot plasma that condenses onto the feature. Like this, a dynamic, cool and dense structure is built up in the solar corona. In this contribution, I will present the formation mechanism and properties of the simulated prominence for different setups of our configuration, as well as results from the chromospheric (NLTE) extension of the simulation.

Speaker: Lisa-Marie Zessner (Max Planck Institute for Solar System Research)

Topic3_Contr39_Zessner.pptx

Multi-scale energy release, flares and coronal mass ejections

Convener: Francesca Zuccarello (Università di Catania)

33 Exploring Coronal Mass Ejections: An Overview

Coronal mass ejections (CMEs) are huge eruptions of magnetized plasma from the Sun that travel into interplanetary space. These energetic and complex phenomena, when they interact with Earth's magnetic field, can cause significant disruptions. Due to their potential impact, there has been a strong focus on studying CMEs to predict them well in advance of their arrival at our planet. In my presentation, I will provide an update on the progress made in this area, highlighting recent findings on CME source regions, eruption mechanisms, and their movement through the solar atmosphere. I will also discuss the challenges and opportunities for studying CMEs, including potential improvements through recent and upcoming space missions.

Speaker: Marilena Mierla

Topic4_Contr49_Mierla.pdf

Coffee break and poster session 1

Multi-scale energy release, flares and coronal mass ejections

Convener: Francesca Zuccarello (Università di Catania)

34 Refining Coronal Mass Ejection Dynamics: A Semi-Analytical Flux-Rope Model Incorporating Magnetic Erosion

Our study aims to advance our understanding of the complex interactions between Coronal Mass Ejections (CMEs) and the solar wind/interplanetary magnetic field (IMF) system. We introduce a novel flux-rope semi-analytical MHD model that incorporates a comprehensive approach to understanding the impact of magnetic erosion and virtual mass on the propagation of CMEs. This model explores the profound effects of these processes, specifically focusing on the consequences of magnetic reconnection, which progressively diminishes the azimuthal magnetic flux and the mass of the outer shell of CME structures. With this study, we investigate how these forenamed processes can influence the dynamics of fast CMEs, affecting their anticipated arrival times in the near-Earth space environment and the space weather forecasts in general.

Speaker: Mr Sotiris Stamkos (University of Ioannina)

Topic4_Contr85_Stamkos.pptx

35 What can we learn about coronal mass ejections from their associated coronal dimmings?

Coronal dimmings are sudden decreases of the solar EUV and soft X-ray emission caused by coronal mass ejection (CMEs). From the solar observations, we know that dimming regions map to the bipolar ends of closed magnetic field lines that become stretched or temporarily opened during an eruption, and the decrease in the emission is a result of the depletion of coronal plasma caused by the expansion and mass loss due to the CME. We present recent statistical studies that showed distinct correlations between characteristic CME mass and speed with key parameters of the associated coronal dimmings such as their spatial extent and intensity drop. We also discuss how the locations of the coronal dimmings may help us to better understand the origin of the eruption. Finally, we outline how full-Sun EUV measurements provide us with a means to connect the solar observations to late-type stars, and to develop methods for the detection of stellar coronal mass ejections.

Speaker: Prof. Astrid Veronig (Institute of Physics & Kanzelhöhe Observatory, University of Graz, Austria)

topic4_212_Veronig.pdf

36 Rare case of the three-part structure of coronal mass ejection observed in low coronal signatures

We present a rare case of a three-part solar coronal mass ejection (CME) observed in the low corona on March 28, 2022. We observe a bright core/prominence, dark cavity, and a bright CME leading edge in SolO/EUI and STEREO-A/EUVI. We perform 3D reconstructions of the filament eruption from three vantage points: SolO, STEREO-A, and SDO. The filament height increased from 28 to 616 Mm over 30 minutes, with a peak velocity of 648 ± 51 km/s and a peak acceleration of 1624 ± 332 m/s². At 11:45 UT, the filament deflected by ~12 degrees, reaching a height of 841 Mm. The bright CME leading edge, a quasi-spherical CME shock, grows from 383 Mm to 837 Mm between 11:25 and 11:35 UT. The distance between the filament apex and the CME leading edge doubled from 93 to 212 Mm over 10 minutes. Using the DIRECD method, we studied the expansion of coronal dimming as an indicator of early CME propagation. This method uses a cone model to approximate an expanding CME at the end of the dimming's impulsive phase, estimating parameters such as direction (inclined 6 degrees from the radial expansion), half-width (21 degrees), and cone height (1.12 Rs), where the CME remains connected to the dimming and leaves footprints in the low corona. The reconstructed cone aligns closely with the observed filament shape. Extrapolating filament and CME outer edge heights to LASCO/COR2 times, we found the cone matched the CME shape, with fainter CME parts corresponding to far-side cone projections.

Speaker: Dr Tatiana Podladchikova (Skolkovo Institute of Science and Technology)

Topic4_Contr54_Podladchikova.pptx

37 CME small-scale structures: new insights from white light observations taken between 0.06 -- 1 AU

Parker Solar Probe (PSP) and Solar Orbiter (SO) observe the Sun from unprecedented close-in orbits out of the Sun-Earth line. Due to the highly elliptical orbits of the respective S/C, they cover varying heliocentric distances during their encounters around the Sun. They both provide high-resolution observations of the heliosphere through their white light heliospheric imagers: PSP/WISPR and SO/SoloHI. Using also observations from the HI-1 heliospheric imager onboard STEREO-A (ST-A) at about 1 AU, we catalog a set of events observed simultaneously from at least two of the imagers and highlight their morphological differences when observed from different viewpoints. This allows us to investigate the 3D location, morphology, and evolution of the internal magnetic fine structures in the interiors of CMEs. We derive the three-dimensional information of small-scale magnetic structures for the events on December 8, 2022, and on September 24, 2023. ST-A/HI1 and PSP/WISPR (between 0.11-0.16 AU) observed the former (a filament-related CME) from a similar longitudinal range. Still, they show a different global appearance of the CME, presumably because of the shorter line-of-sight integration of WISPR. For the event on September 24, 2023, WISPR (at 0.18 AU) and SO/SoloHI (at 0.4 AU) were oppositely located in longitude and, though observing the event from different distances, their observations reveal many common features in their FoV. We demonstrate that the CME consists of various morphological groups of fine structures, which can be related back to the Sun, and explore how CME structures appear differently when observed from different viewpoints.

Speaker: Greta Cappello (University of Graz)

Topic4_Contr204_Cappello.pptx

38 Synthetic Parker Solar Probe Observables of an Idealized Pseudostreamer CME Eruption

Coronal pseudostreamer flux systems have a specific magnetic configuration that influences the morphology and evolution of coronal mass ejections from these regions. Here we present the analysis of a recent, high-resolution magnetohydrodynamic simulation of a CME eruption from an idealized pseudostreamer configuration through the construction of synthetic remote sensing and in-situ observational signatures. We examine the pre-eruption and eruption signatures in the low corona and through the extended corona corresponding to typical EUV imaging and white light coronagraph fields-of-view. We calculate synthetic observations corresponding to several Parker Solar Probe-like trajectories at ~10Rs to highlight the fine-scale structure of the CME eruption in synthetic WISPR imagery and the differences between the in-situ plasma and field signatures of flank and central encounter trajectories. Finally, we conclude with a discussion of several aspects of our simulation results in the context of interpretation and analysis of current and future Parker Solar Probe data.

Speaker: Benjamin Lynch (Space Sciences Laboratory, University of California--Berkeley)

Topic4_Contr251_Lynch.pptx

39 Helical Structures Captured by Metis During a Polar Crown Prominence Eruption

We present observations of a solar eruption captured by Metis onboard Solar Orbiter on October 12, 2022, during its perihelion passage. Using total brightness data, we observed the outward propagation of helical structures for more than three hours, extending up to 3 solar radii following a polar crown prominence eruption. These structures exhibited a notable trend: their inclination decreased as their polar angle and height increased. Further analysis, including examination of EUI images, revealed evidence of an eruptive flux rope in the lower corona with distinguishable footpoints as the source of these helical structures.
We also performed a comparative analysis with a high-resolution magnetohydrodynamic simulation of bursty interchange reconnection, finding strong similarities in the evolution of the observed and simulated structures. The white light structures in the simulation form as dense plasmoid plasma intermittently launched along open field lines when the plasmoids are ejected. The same ejection process also launches torsional Alfven waves, which may act as seed perturbations to form magnetic switchbacks within the solar wind. These observations and simulations suggest that sustained bursty interchange reconnection occurred following the eruption. Additionally, they demonstrate a key new observable associated with the bursty interchange reconnection process, providing a link between coronal dynamics and in-situ measurements such as those of switchbacks observed by Parker Solar Probe.

Speaker: Paolo Romano (Istituto Nazionale di Astrofisica (INAF))

Topic4_Contr244_Romano.pptm

Wednesday 11 September

Multi-scale energy release, flares and coronal mass ejections

Convener: Ioannis Kontogiannis (Leibniz-Institute for Astrophysics Potsdam (AIP))

40 Solar Eruptions Triggered by Flux Emergence Below or Near a Coronal Flux Rope

Observations have shown a clear association of filament/prominence eruptions with the emergence of magnetic flux in or near filament channels. Magnetohydrodynamic (MHD) simulations have been employed to systematically study the conditions under which such eruptions occur. These simulations to date have modeled filament channels as two-dimensional (2D) flux ropes or 3D uniformly sheared arcades. Here we present MHD simulations of flux emergence into a more realistic configuration consisting of a bipolar active region containing a line- tied 3D flux rope. We use the coronal flux-rope model of Titov et al. (2014) as the initial condition and drive our simulations by imposing boundary conditions extracted from a flux-emergence simulation by Leake et al. (2013). We identify three mechanisms that determine the evolution of the system: (i) reconnection displacing foot points of field lines overlying the coronal flux rope, (ii) changes of the ambient field due to the intrusion of new flux at the boundary, and (iii) interaction of the (axial) electric currents in the pre-existing and newly emerging flux systems. The relative contributions and effects of these mechanisms depend on the properties of the pre-existing and emerging flux systems. Here we focus on the location and orientation of the emerging flux relative to the coronal flux rope. Varying these parameters, we investigate under which conditions an eruption of the latter is triggered.

Speaker: Tibor Torok

Topic4_Contr293_Torok.pptx

41 The Role of Magnetic Reconnection in the Formation and Evolution of Eruptive Magnetic Flux Ropes

Magnetic flux rope (MFR) is generally considered the core structure of coronal mass ejections (CMEs). However, how an MFR forms and develops into a CME has been elusive. Through a series of observational studies, we found that a coherent magnetic flux rope may originate from a ‘seed’ MFR that is formed through magnetic reconnection in a current layer underneath a sheared magnetic arcade, as a result of the convalescence of plasmoids formed in the current layer. During the eruption, while magnetic reconnections continually convert overlying, untwisted magnetic flux into twisted flux to help further build up the pre-existent MFR, they also restructure the MFR through reconnections between the MFR and the ambient field. The restructuring may go as far as to completely replace the original MFR’s flux, which is manifested by drastic footpoint migration, highlighting the 3D nature of magnetic reconnection; and alternatively may dissolve the MFR, while simultaneously exciting a shock wave, revealing an imploding process intrinsic to magnetic reconnection.

Speaker: Rui Liu

Topic4_Contr75_Liu.pptx

42 Identifying and Tracking CME Flux Ropes On The Example of AR12473

The study of coronal mass ejection triggering and early evolution necessitates numerical modelling, as measuring the coronal magnetic field is challenging. A key ingredient of the modelling efforts is to reliably identify and track the underlying magnetic structure of the eruption, the magnetic flux rope (MFR), in the simulation data. To achieve this, we developed an extraction and tracking scheme for MFRs, wrapped into a user-friendly GUI called GUITAR (GUI for Tracking and Analysing flux Ropes). The method builds upon a suitable MFR proxy, such as the twist of magnetic field lines, and combines it with mathematical morphology (MM) algorithms. The basic principle of MM algorithms is the comparison of an image with a so-called structuring element. In the context of MFRs, these algorithms are useful tools to identify the MFRs. We apply this scheme with GUITAR to a time-dependent data-driven magnetofrictional simulation of active region AR12473. We identify the MFR, analyse the evolution of its properties and track the flux rope from its formation until the eruption from the simulation domain. Furthermore, we demonstrate that it is a multi-MFR structure and analyse its large-scale evolution and triggering mechanism.

Speaker: Andreas Wagner (University of Helsinki)

Topic4_Contr171_Wagner.pptx

43 Sunspot Scars: New Features of Solar Flux Rope Footpoints

The properties of pre-eruptive structures of coronal mass ejections (CMEs) are important for forecasting solar eruptions, the former of which are usually quantified by measuring the properties of their footpoints in observations. However, the matter of how to identify the footpoints of pre-eruptive structures and how to do so with the use of ground-based instruments still remains elusive. In this work, we reveal for the first time an arc-shaped structure intruding in the sunspot umbra, which we call a “sunspot scar”, through analysing a CME event on July 12, 2012 and two CME events from observationally inspired magnetohydrodynamic simulations performed by OHM and MPI-AMRVAC. The sunspot scar displays a more inclined magnetic field relative to that in the surrounding umbrae, and it is manifested as a light bridge in the white light passband. For both the pre-eruptive and CME flux ropes, the sunspot scars mark the edges of their footpoints, as the field lines anchored in the sunspot scar are spatially at the transition between the flux rope and the coronal loops and temporally in the process of the slipping reconnection which builds up the flux rope. Therefore, the sunspot scar provides a new method for the identification of pre-eruptive and CME flux rope footpoints. Furthermore, it opens up a new perspective for studying the evolution of solar eruptions with the extremely high-resolution photospheric observations from the current and next-generation giant ground-based telescopes.

Speaker: Dr Chen Xing (Nanjing University)

44 Unveiling the Global Magnetic Topology with Physics-Informed Neural Networks

The 3D coronal magnetic field is the decisive component to understand the formation and eruption of flux ropes in the solar corona. Non-linear force-free magnetic field extrapolations are a frequently applied method to provide a realistic estimate of the coronal magnetic field from photospheric vector magnetograms but are typically limited to small simulation volumes.
We present a novel approach based on Physics-Informed Neural Networks, to perform force-free magnetic field extrapolations of the global solar magnetic field. Our method uses full-disk vector magnetograms from SDO/HMI, and directly models highly twisted quiet-Sun filaments, coronal holes, and complex active region fields, that are in agreement with observations from SDO/AIA in extreme ultraviolet.
We use our method to study the eruption of a trans-equatorial filament on February 5th 2016 and its connection to a quiet-Sun filament eruption. The global extrapolation reveals the magnetic connectivity across the solar equator and interaction with an open-flux region. Furthermore, our model shows the large-scale connectivity that could link to a sympathetic filament eruption. These findings highlight the importance of the global magnetic topology, both for small scale reconnection and large topological reconfigurations. We conclude with an outlook, where we apply this approach to estimate the open magnetic flux and show that highly twisted field configurations play a significant role for the formation of open flux regions.

Speaker: Robert Jarolim (University of Graz)

Topic4_Contr301_Jarolim.pptx

45 Can we find distinct flare precursors observed with the IRIS spectrograph?

Solar flare prediction has often been studied with data from the Solar Dynamics Observatory (SDO), which provides images of the full solar disk in different wavelength bands, probing different heights of the solar atmosphere, including the photospheric magnetic field. Recent studies have shown that spectroscopic data such as observations with the Interface Region Imaging Spectrograph (IRIS) may contribute to improving solar flare predictions in the future.
IRIS has a limited field of view and thus variable pointing, and additionally, the spectrograph slit only covers parts of an active region, which limits its potential for long-term forecasting. Therefore, we aim to study short-term spectral flare precursors observed with IRIS, occurring up to 1 hour before flare onset.
We use machine learning techniques to automatically mark where a flare occurs in an active region and extract the time-series of spectra of these pixels. We train classification models specifically to highlight such areas, solely from the shape of the spectra before the flare. Additionally, we investigate if there are distinct spectral shapes occurring before each flare, that can be categorized as strong flare precursors.
We find that the areas highlighted by the machine learning models match well with the later location of the flare, and that the Magnesium II h&k triplet emission is a strong precursor, which often occurs at the future onset location of a solar flare. We speculate that this is because of chromospheric heating before flares.

Speaker: Mr Jonas Zbinden (Astronomical institute University of Bern)

Topic4_Contribution192_Zbinden.pptx

Coffee break and poster session 2

Multi-scale energy release, flares and coronal mass ejections

Convener: Ioannis Kontogiannis (Leibniz-Institute for Astrophysics Potsdam (AIP))

46 3D Magnetic reconnection and energy release in solar flares and eruptions

The three-dimensional magnetic reconnection geometries have recently been shown to be present in solar flares, providing explanations for various observed phenomena, including evolution of sigmoids, drift of the erupting flux rope legs, and the shape of solar flare arcades. We review the observational evidence for these processes and their consequences for space weather. Particular emphasis is paid to related energy release phenomena occuring on short timescales, including HXR and radio bursts, fast slippage of flare loops, intermittent heating of the solar flare atmosphere, and the possibility that the flaring atmosphere is strongly out of equilibrium.

Speaker: Jaroslav Dudík (Astronomical Institute of the Czech Academy of Sciences)

2024-09-11_ESPM-17_Dudik_Final.pptx

2024-09-11_ESPM-17_Dudik_slide10_Dudik2019_movie.mp4

2024-09-11_ESPM-17_Dudik_Slide11_Dudik2022_movie1.mpg

2024-09-11_ESPM-17_Dudik_Slide13_Dudik2022_movie2.mpg

2024-09-11_ESPM-17_Dudik_Slide14_Dudik2014_movie1.mpg

2024-09-11_ESPM-17_Dudik_Slide14_Dudik2014_movie2.mpeg

2024-09-11_ESPM-17_Dudik_slide2_Xing2024_movie.mp4

47 X-ray observations of small-scale flaring energy releases

X-ray observations provide insight into the energy release in solar flares - the heated material and accelerated particles detectable via thermal and non-thermal bremsstrahlung emission respectively. We present observations of small active regions flares and even smaller quite Sun “flares” observed with the Nuclear Spectroscopic Telescope Array (NuSTAR), a highly sensitive telescope providing imaging spectroscopy > 2 keV. With active region microflares we show that heating to ~10 MK and acceleration of electrons is still present, much like larger flares. We present some microflares that were jointly observed with NuSTAR and the Spectrometer Telescope for Imaging X-rays (STIX) on Solar Orbiter, providing different viewing angles of the energy release. We also present some quiet Sun (non-active region) impulsive energy releases observed with NuSTAR during the recent solar minimum, investigating whether “flare-like” energy release continues outwith active regions. All these observations are also considered in the context of EUV emission seen by the SDO/AIA and softer X-ray with Hinode/XRT.

Speaker: Dr Iain Hannah (University of Glasgow)

Hannah_ESPM17.pdf

48 Analysis of flare ribbon fine structures using high-resolution observations

The mechanism of energy release from solar flares are still not fully understood and the study of small-scale features is an important aspect toward this understanding. Flare ribbons act as the footpoints of a flare and are crucial to know the process of flare reconnection. We present here a study about the fine structures of flare ribbons using a high resolution observations using the Swedish 1-m Solar Telescope (SST), the Atmospheric Imaging Assembly (AIA), and the Interface Region Imaging Spectrograph (IRIS). The high-resolution SST observations offer spectroscopic data in Hα, Ca II 8542 Å and Hβ lines, which we use to analyze plasma blobs along the flare ribbon. Within the eastern flare ribbon, chromospheric blobs were detected in the red wing of Ca II 8542 Å, Hα, and Hβ. A comparison of plasma blobs in Hβ observations and Si IV 1400 Å has also been performed. These plasma blobs are observed as circular structures having widths from 150 km - 180 km. Intensity profiles at these blob locations show a red wing asymmetry. We conclude that the chromospheric plasma blobs in the flare ribbon are likely formed due to a fractured reconnection process within the flare current sheet, supporting the theory of a direct link between fine-structure flare ribbons and flare current sheet tearing. We believe our observations represent the highest resolution evidence of fine-structure flare ribbons to date.

Speaker: Jonas Thoen Faber (Rosseland Centre for Solar Physics, University of Oslo)

Topic4_Contr48_Faber.pptx

49 Turbulent Dynamics in Gradual-Phase Flare Loops: Insights from 3D MHD Simulations

The gradual phase is a relatively quiet stage in the evolution of a flare, encompassing most of its duration. During this phase, the hot and dense flare loops, formed by reconnection and chromospheric evaporation in the impulsive phase, gradually cool down and decrease in density. We propose and demonstrate with 3D simulation that the seemingly calm gradual-phase flare loops are filled with low-speed turbulent motions until the flare ends. The formation of these motions is related to the characteristics of the flare loops: high density. Due to the relatively small size of the flaring regions, the density variation length scale is much smaller than the atmospheric scale height at the corresponding temperature, involving the Lorentz force in maintaining the density gradient. The force balance between the Lorentz force and thermal pressure is unstable, leading to Rayleigh-Taylor type instabilities that grow on sub-minute timescales within the loops, resulting in sustained turbulent motions until the region returns to typical coronal density. Our research uncovers an energy conversion pathway in flares: chromospheric evaporation carries significant energy into the flare loops, part of which converts into transverse wave energy through instabilities, with these waves then transporting energy back to the lower atmosphere.

Speaker: Wenzhi Ruan (Max Planck Institute for Solar System Research)

Topic4_Contr197_Ruan.pptx

50 Understanding the thermal and magnetic properties of an X-class flare in the low solar atmosphere

Recent exploitation of spectropolarimetric data has significantly enhanced our understanding of the dynamical and magnetic responses of the photospheric and chromospheric layers during the rapid energy release that occurs in solar flares. In this context, we utilized high-resolution observations from 22nd October 2014, captured during an X1.6 confined flare by the Interferometric Bidimensional Spectropolarimeter (IBIS) instrument, which observes the full Stokes parameters for the Fe I 6173 Å and Ca II 8542 Å transitions.

We employed the newly developed Departure Coefficient Aided Stokes Inversion based on Response Functions (DeSIRe) code to infer the spatial distribution and vertical stratification of the atmospheric parameters in the photospheric and chromospheric layers. Our findings indicate significant temperature increases and pronounced upflows within the chromospheric flare ribbon, suggesting that the flaring event is generating hot material moving upwards. Conversely, the photosphere shows no discernible temperature rise or strong velocities, implying that the flaring event's impact is predominantly in the middle and upper layers.

The magnetic field vector information reveals relatively smooth stratifications with height for both magnetic field strength and inclination. Additionally, we observe that the spatial locations within the flare ribbon exhibit a significant depression in the height of formation (or sensitivity) for the chromospheric line, while no clear indication of this effect is found for the Fe I transition. These results confirm that, in the low atmospheric layers, the primary impact of flaring activity occurs at chromospheric levels.

Speaker: Fabiana Ferrente (Università Degli Studi di Catania)

Topic4_Contr57_Ferrente.pptx

51 Chromospheric evaporation as observed by STIX from the perihelion of Solar Orbiter

During the impulsive phase of the flare, beams of non-thermal electrons move from the magnetic reconnection site towards the chromosphere, where the density increases rapidly. Therefore, we can estimate the plasma density distribution along the non-thermal electrons path directly from the observations of the energy-altitude relation obtained for the HXR footpoint sources. Its shape is determined by changing plasma density, the power-law distribution of non-thermal electrons and a degree of ionisation within footpoints. Previous analysis of the chromospheric density showed power-law dependence. Here, we present a moderate solar flare observed by the Spectrometer Telescope for Imaging X-rays (STIX) onboard the Solar Orbiter (SolO) mission. During the flare, SolO was very close to the Sun (~ 0.32 AU) offering imaging of the solar flare’s HXR footpoints with a spatial resolution better than previous HXR telescopes. HXR images were reconstructed with 2-5 keV energy and 10 s time resolutions. The observed relation is not power-law. It reveals details showing the chromospheric evaporation on a wide range of altitudes. We identified two regions within the lower part of the flare legs. Deep in the chromosphere, the moving plasma appeared abruptly with velocities at 300 km/s, while in the loop legs plasma flows look to be more gradual (up to 50 km/s). These details show that the HXR images obtained for the perihelion passage contain new pieces of information about plasma dynamics during the impulsive phase of a solar flare.

Speaker: Katarzyna Mikuła (Space Research Centre, Polish Academy of Sciences)

Mikula_Katarzyna_Talk_ESPM17.pptx

Lunch break

Social excursions

Social excursions programme.pdf

Thursday 12 September

Multi-scale energy release, flares and coronal mass ejections

Convener: Dr Alessandro Bemporad (Istituto Nazionale di Astrofisica (INAF))

52 The fine scales of solar flares

The quest for ever higher spatial and temporal resolution in solar physics can sometimes be thwarted by photon flux. However, in solar flares the greatly increased output across most of the electromagnetic spectrum means that we can often take advantage of high spatial and temporal resolution simultaneously. The rapid evolutionary timescales of flares certainly merit this effort. This talk will review some recent results in which observations at fine spatial and temporal scales are used to explore the properties of solar flare magnetic energy release and energy transport. The emphasis will be on chromospheric and transition region observations of flare footpoints and ribbons. Topics will include ribbon fine structure and what it reveals about coronal processes, and footpoint timing measurements and the chromospheric source heights, both of which help constrain energy transport models.

Speaker: Lyndsay Fletcher (University of Glasgow)

topic4_contr313_fletcher.pptx

53 Probing particle acceleration and transport through behind-the-limb gamma-ray Solar flare observations

Observations of greater than 100 MeV gamma-ray emission from solar flares from active regions located behind the visible solar disk pose interesting questions regarding the acceleration sites and mechanism, the transport and interaction points of the accelerated particles during these events. Two of the most popular scenarios to explain these observations are (a) acceleration at the coronal mass ejection (CME)-driven shock with back precipitation to the solar atmosphere and (b) trapping of flare-accelerated ions in extended coronal loops or additional acceleration and release into the loop. In this talk I will discuss the most recent results from the Large Area Telescope onboard the Fermi Space Telescope that show evidence in support of both of these scenarios during behind-the-limb solar flares.

Speaker: Melissa Pesce-Rollins (INFN-Pisa)

BTLflares_pescerollins.pdf

54 High-Resolution Observations from the Solar Orbiter Major Flare SOOP Campaign: Insights from X-ray and Fast Cadence EUV Observations of Solar Flares

The Solar Orbiter's Major Flare SOOP (Solar Orbiter Observing Plan) campaign successfully captured several M- and C-class flares as the spacecraft approached perihelion in Spring of this year (March and April). This campaign provided unprecedented observations of solar flare dynamics through high-resolution extreme ultraviolet (EUV) observations using the High Resolution Imager (HRIEUV) of the Extreme Ultraviolet Imager (EUI), combined with X-ray observations from the STIX instrument. The Major Flare campaign was designed to capture the most detailed images of solar flares. The HRIEUV telescope operated in a short exposure mode, acquiring EUV images at an unprecedented 2-second cadence, achieving the fastest cadence non-saturation images of a flare to date. These observations provide unparalleled detail in the early stages of flare development, and the correlation of X-ray and EUV data offers new insights into the energy release and particle acceleration processes during solar flares. This presentation provides an overview of the campaign and highlights the initial results, focusing on the X-ray data and the fast cadence, short exposure EUV observations obtained from HRIEUV. In particular, a detailed analysis of the March 19th M-class flare will be highlighted.

Speaker: Laura Hayes (European Space Agency)

Topic4_flares_223_Hayes.pptx

55 The May 2024 flare sequence: a rich opportunity for QPP analysis

Monster active regions 13663 and 13664 produced not less than 18 X-class solar flares between May 3 and May 15, before rotating out of view from Earth. Despite this, AR 13664 continued to exhibit significant activity, generating numerous events observed by instruments onboard the Solar Orbiter mission. This extraordinary sequence of strong flares not only delighted sky watchers with remarkable auroras but also provides valuable data for the analysis of Quasi-Periodic Pulsations (QPPs).

These flares were recorded by various instruments across multiple spectral ranges and from different vantage points. Some flares were associated with coronal mass ejections (CMEs), filament eruptions, or solar energetic particles (SEPs), and were observed both on-disk and at the solar limb. This dataset presents a unique opportunity to investigate the influence of flare characteristics on QPPs.

In this study, we analyze QPP observations from several solar missions, including GOES, PROBA2, Solar Orbiter, SDO, to investigate if the general trend of QPPs also holds for this serie of very large flares.

Speaker: Marie Dominique (Royal Observatory of Belgium)

Topic4_Contr215_Dominique.pptx

56 First comparison of MSDP spectroscopic observation of the C1.6 solar flare with FLARIX NLTE simulations

For the first time we present comparison of advanced FLARIX NLTE time-dependent numerical simulations of flaring emission with spectral observations of a compact C1.6 GOES-class flare recorded with MSDP (Multichannel Subtractive Double Pass) imaging spectrograph installed at the Białków Observatory. The high time resolution (50 ms) MSDP spectral data, enabled comprehensive analysis of H-alpha line profiles and light curves measured within the chromospheric flaring sources. For FLARIX simulation an initial atmospheric model similar to VAL-C, but with a modified temperature in the upper chromosphere, was applied. We also used, as an input parameters, increased to sub-second time resolution non-thermal electron (NTE) beam's parameters obtained from RHESSI satellite. To achieve it the basic 4-sec resolution data were modulated using the de-modulated (to 250 ms) hard X-ray (HXR) RHESSI flux. Synthetic H-alpha line profiles obtained from FLARIX were compared with the observed spectra. During the impulsive phase of the flare, the general evolution of the observed and synthetic H-alpha line intensity were in good agreement, but some differences were observed in intensities in various parts of the H-alpha line profile. Variations of the energy flux of NTEs was in strong correlation with H-alpha emission during the analysed HXR pulse. Considering various effects, such as the filling factor FF = 0.20 influenced on observed emissions, relatively good agreement between theoretical and observed lines was achieved.

Speaker: Arkadiusz Berlicki (Centre of Scientific Excellence - Solar and Stellar Activity, University of Wroclaw, Poland)

MSDP_FLARIX_MODEL_Contr316_Berlicki.pdf

ESPM-17 group picture

Coffee break and poster session 2

Diagnostic tools and numerical methods in solar physics

Convener: Sophie Masson (LPP)

57 The inversion of spectropolarimetric data and machine learning: a story about old friends and their adventures

Over the past few decades, advancements in solar instrumentation, both ground- and space-based, have resulted in a large amount of high-quality spectral and spectro-polarimetric data. It is of great importance for the solar community to reliably extract the physical information encoded in these observations. The inversion of this type of data has been established as the most precise method to achieve this aim. I will examine the fundamental concepts and difficulties associated with this technique and highlight the endeavors to integrate it into the domain of machine and deep learning.

Speaker: Alberto Sainz Dalda (Bay Area Environmental Research Institute/Lockheed Martin Solar and Astrophysics Laboratory)

58 Improved reconstruction of solar magnetic fields from imaging spectropolarimetry through spatio-temporal regularisation

Determination of solar magnetic fields with a spatial resolution set by the diffraction limit of a telescope is difficult because the time required to measure the Stokes vector with sufficient signal-to-noise ratio is long compared to the solar evolution timescale. This difficulty becomes greater with increasing telescope size as the photon flux per diffraction-limited resolution element remains constant but the evolution timescale decreases linearly with the diffraction-limited resolution.

The magnetic field vector tends to evolve more slowly than the temperature, velocity, or microturbulence. We exploit this by adding spatio-temporal regularisation terms for the magnetic field to the linear least-squares fitting used in the weak-field approximation, as well as to the Levenberg-Marquardt algorithm used in inversions. The other model parameters can be allowed to change in time and space with far less restrictive constraints. Our results show that the noise in the reconstructed magnetic field vector is greatly reduced by spatio-temporal regularisation, while all other model parameters can capture the faster variability of the atmosphere imprinted in the line profiles.

These methods are fundamentally important for the interpretation of data from the new generation of 4-m telescopes like DKIST and the planned EST, where solar evolution time will be critically low.

Speaker: Jaime de la Cruz Rodriguez (Institute for Solar Physics, Stockholm University)

Topic5_Contr92_delaCruz.key

Topic5_Contr92_delaCruz.pdf

59 Modeling the polarization of strong chromospheric lines and its magnetic sensitivity

A primary goal in today's solar physics research is to develop remote sensing methods for measuring the elusive magnetic fields of the chromosphere and transition region. A very promising strategy is to exploit the fingerprints that the magnetic field leaves in the polarization of strong resonance lines through the joint action of the Zeeman, Hanle, and magneto-optical (MO) effects. Significant efforts have been put in this research field during the last decade, from both the observational and theoretical point of view. In this talk, we first highlight the diagnostic potential of the aforementioned effects, recalling the underlying physics and pointing out the computational aspects inherent to their modeling. Subsequently, we present a new code capable of solving the radiative transfer problem for polarized radiation in strong resonance lines, accounting for the Zeeman, Hanle, and MO effects, as well as for partial frequency redistribution (PRD) in scattering processes, in comprehensive 3D models of the solar atmosphere. The code, named TRIP, provides synthetic data of unprecedented accuracy, which are crucial to reliably interpret a variety of spectropolarimetric observations of chromospheric lines, including those of HI Ly-α and MgII h and k provided by the three CLASP sounding rocket experiments. Moreover, it can be used to generate accurate datasets for the training of machine learning inversion algorithms.

Speaker: Luca Belluzzi (Istituto ricerche solari Aldo e Cele Daccò (IRSOL))

60 Parametrization of SHARP Vector Magnetic Field Using Disentangled Representation Learning

Contemporary solar physics deals with the increasing amount of high-dimensional data, making it an excellent case for the application of machine learning (ML) algorithms. Synoptic full-disk observations with the Solar Dynamics Observatory (SDO) are one example, allowing us to follow the solar magnetic activity over more than one solar activity cycle and to study its local and global facets. The Space-weather HMI Active Region Patches (SHARP) vector magnetic field (VMF) maps and parameters, based on Helioseismic and Magnetic Imager (HMI) full-disk observations, are developed for studying the magnetic evolution of individual active regions and flare triggering mechanisms. We present a method for active region parametrization by combining empirical parameters and ML-extracted features based on SHARP maps. Time series of SHARP VMF maps are used as input for Disentangled Variational Autoencoder (VAE), a Disentangled Representation Learning (DRL) algorithm, which facilitates the extraction of low-dimensional feature representation. The power of the VAE model lies in its ability to encode generalized information about nonlinear dynamical systems, in this case a solar active region, where each feature represents a particular aspect of the input data. We demonstrate how the VAE-based features can be used to identify and study the stages of the magnetic patches evolution in combination with the SHARP empirical parameters, relating empirical and learned features. Furthermore, empirical dataset enhanced with ML features can be used to analyze the development of individual active regions and searching for eruption precursors.

Speaker: Ekaterina Dineva (Centre for mathematical Plasma-Astrophysics)

Topic5_Contr308_Dineva.pptx

61 Implementation of thermal conduction energy transfer codes in the Bifrost Solar atmosphere MHD solver

Thermal conductivity provides important contributions to the energy evolution of the upper solar atmosphere, behaving as a non-linear concentration-dependent diffusion equation. Computational discretisation limits the operation of solving such terms due to numerical instabilities and other error build-up. Recently, different methods have been offered as best-fit solutions to these problems in specific situations, but their limitations and total range in other scenarios is rarely discussed. Therefore, we rigorously test the different implementations of solving the conductivity flux, in the massively parallel MHD solver code, Bifrost. We compare the differences and limitations of explicit vs. implicit methods, and analyse the convergence of a hyperbolic approximation. Among the tests, we use a newly derived 1st-order self-similar approximation to compare the efficacy of each method analytically in a 1D pure-thermal scenario. The results give guidelines for when to use each method, and the variables that might affect a certain method’s efficiency or accuracy. We discuss the optimisation of parameters in each method, and weaknesses that are not covered suitably by the current implementations.

Speaker: George Cherry (Rosseland Centre for Solar physics, universitetet i oslo)

Topic5_Contr151_Cherry.pptx

Lunch break

Outreach in Solar Physics

A huge number of solar outreach and educational activities are carried out across Europe (for example linked to European projects such as EST and ESA’s Solar Orbiter) and beyond. Some of these projects are linked to the Arts, visual art (such as STFC’s SunSpaceArt) and music. This session is aimed at both informing the solar physics community about this work, sharing ideas and resources, and encouraging young solar researchers to engage with and develop outreach activities.

It is paramount that we share our knowledge and research about the Sun, solar wind, space weather and the heliosphere with the public, politicians, and the next generation (students and school children). The press and social media are, for example, a great way to reach the public. This is very timely with the Sun approaching solar maximum, large sunspot groups, solar flares and extensive auroral displays. Sharing our ideas and resources will enable us to reach further and have more impact.

This lunchtime session will comprise a few short introductory talks (5-10mins each) and a panel discussion. Please join us.

Conveners: Helen Mason (University of Cambridge), Hugh Hudson (UC Berkeley / U of Glasgow)

ESPM17_outreach_session_program.pdf

62 Outreach in Solar Physics

Please find the detailed program here:

https://indico.ict.inaf.it/event/2971/timetable/#20240912

Speakers: Helen Mason (University of Cambridge), Hugh Hudson (UC Berkeley / U of Glasgow)

Diagnostic tools and numerical methods in solar physics

Convener: Sophie Masson (LPP)

63 Chromospheric Magnetic Field Reconstruction through Neural Field Assisted Spectropolarimetric Inversions

Spectropolarimetric observations provide valuable information about the physical conditions in the solar atmosphere, particularly the magnetic field. However, traditional pixel-by-pixel inversion techniques fail to capture the inherent spatial and temporal coherence of the solar atmosphere. To address this limitation, we propose a novel approach that utilizes neural fields (NFs) to perform spectropolarimetric inversions. NFs leverage compact neural network parameterization to represent continuous physical quantities. This allows us to impose spatio-temporal constraints on the inferred magnetic field, improving the fidelity of the reconstruction compared to the standard pixel-wise approach, especially in noisy scenarios.

We demonstrate the superior performance of NFs in performing chromospheric inversions under the weak-field approximation (WFA) in different spectropolarimetric observations from the Swedish 1-m Solar Telescope (SST). Moreover, the NF framework seamlessly integrates external constraints, such as alignment with the orientation of the chromospheric fibrils or similarity to pre-computed magnetic field extrapolations, further improving the fidelity of the inferred magnetic field. This work showcases the potential of NFs for future instruments with large fields of view, thanks to their compact representation and the ability to impose spatio-temporal constraints to improve the magnetic field reconstruction in the solar atmosphere.

Speaker: Carlos Jose Diaz Baso (Oslo University)

Topic5_Contr294_DiazBaso.pdf

64 Spectroscopic measurements from Solar Orbiter Full Disk Mosaic

One crucial objective of Solar Orbiter is to explore the connection between the solar surface and the heliosphere. Since March 2022, several Solar Orbiter Observing Plans (SOOP) have been run to address this goal, ranging from Connection Mosaic to Slow Solar Wind. None of these SOOPs gave a global view of the Sun.
A dedicated SOOP, led by the Extreme Ultraviolet Imager, has been designed to scan the full disk using 25 pointings. Each pointing lasted 5-6 minutes, allowing the Spectral Imaging of the Coronal Environment (SPICE) instrument to use only its wider 30" slit to take images, for assembling into the full disk mosaic.

We decided to add a new flavour optimised for SPICE with each pointing lasting 22 minutes. This allowed us to provide proper monochromatic images of the full disk, using the 6" narrow slit, taken in nine spectral lines formed between 10,000K and 1,000,000K.
This SOOP ran twice at a solar distance of 0.7AU, which added the benefit of joint observations with the coronagraph Metis. This allows a thorough view of the spectroscopic features of the full disk, and the preliminary tracking off limb into the heliosphere.

Here we focus on the SPICE spectroscopic measurements, providing intensity maps for the full Sun using selected transition region and coronal lines, and building up basic composition maps to be traced into the heliosphere. This work is ongoing in preparation for the next run (October 2024), and for the first comprehensive polar view from high latitude foreseen for 2025.

Speaker: Alessandra Giunta (STFC RAL Space)

65 Bayes in Space: A Bayesian Deep Learning approach for Coronal Temperature estimation

The Corona, the outermost layer of the Sun, is a region of intense activity and showcases various solar phenomena that affects the thermal distribution of its constituting plasma. The study of the temperature distribution across the corona is essential in understanding different heating mechanisms that lead to the strikingly high temperatures reached by the corona. This distribution can be estimated using photometric observations in multiple bandpasses by imaging surveys like the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory. However, each bandpass covers a range of plasma temperatures and cannot be estimated directly through these observations. The temperatures can be estimated by inverting the intensity or number of photons hitting the detector through the channel passband. We propose an uncertainty based deep learning approach to generate Differential Emission Measure (DEM) maps from solar images, that contain information of the amount of thermal plasma emitted by the solar corona along a line-of-sight at a certain temperature. 
A machine learning approach consists of training a neural network to read AIA images from multiple bandpasses and develop their DEM maps across a range of temperatures as output. While this network can be designed to provide real, non-negative DEM value for each input intensity, it can disrupt the DEM map if it is unsure of its predictions and gives out a wrong output. We introduce an uncertainty in deep learning methods for obtaining the DEM maps from AIA images by incorporating Bayesian techniques like variational dropout and bayes by backdrop, and compare these approaches.

Speaker: Nikita Balodhi (Northumbria University, Newcastle)

bayes_in_space.pptx

66 The Tunable-Imaging Spectropolarimeters/Fixed-Band Imagers for the European Solar Telescope

The European Solar Telescope (EST) will be equipped with a comprehensive suite of state-of-the-art intruments designed to observe the solar atmosphere at high spatial and temporal resolution and with high polarimetric sensitivity. Among them are three Tunable-Imaging Spectropolarimeters and Fixed-Band Imagers (TIS/FBIs) that will provide diffraction-limited measurements of photospheric and chromospheric magnetic fields over large fields of view. Each of these instruments consists of a narrow-band imaging spectropolarimeter and a broad-band imager. The spectropolarimeter is based on a dual Fabry-Perot interferometer and a polarimeter incorporating two nematic liquid crystal variable retarders. The imager will provide context information at the fastest cadence and will allow for reconstruction of the narrow-band images. The three TIS/FBIs will be operated in parallel for high cadence monitoring of the lower solar atmosphere in three or more spectral lines simultaneously, greatly improving the capabilities of existing filtergraphs that measure individual lines sequentially. The TIS/FBIs will provide unprecedented polarimetric sensitivity due to their optimized design and the large photon collecting area of the 4.2 m primary mirror of the telescope.

In this talk we will present the science goals of the EST TIS/FBI instruments. We will also review the current status of the TIS/FBIs, focusing on the main design drivers and the technological solutions adopted in this development phase. The TIS/FBIs are expected to go through a conceptual design review by the end of 2024, together with the other instruments of the EST Instrument Suite.

Speaker: Luis Bellot Rubio (Instituto de Astrofisica de Andalucia (IAA-CSIC))

Topic5_Contr332_BellotRubio.pptx

67 Challenges in forecasting space weather consequences of coronal mass ejections

Intense space weather storms are caused dominantly by coronal mass ejections (CMEs). Their ability to drive significant disturbances in the near-space environments at the Earth and other planets of the solar system is owed to their strong magnetic fields, sustained southward field direction and high solar wind speeds. The magnetic field in CMEs is however difficult to estimate in advance due to the lack of some crucial observations in the solar corona, intrinsic complexities and often drastic evolution and/or interactions occurring during the propagation through the interplanetary medium. This presentation will give an introduction to key challenges pertaining to achieving accurate long-lead time (< 0.5 days) forecasting of the magnetic fields in the heliosphere in two key CME substructures; its turbulent and compressed sheath region and a flux rope where field changes are more organised. Then, an overview of the recent developments in data-driven modelling efforts to estimate the magnetic properties in CME flux rope will be discussed.

Speaker: Emilia Kilpua (University of Helsinki)

Coffee break and poster session 2

Senior Prize Lecture

Convener: Dr Istvan Ballai (University of Sheffield)

68 The never-ending attraction of the Sun’s magnetic personality

Its magnetic field turns the Sun from a dull, middle-aged star into a lively, variable, energetic and attractive subject of study. The field relieves our star from the monotony of a placid, somewhat boring existence, providing it instead with a restless and engaging magnetic personality. This is seen in the play of its ever-changing magnetic features such as mighty sunspots and faculae at the solar surface, majestic prominences, plage and spicules in the chromosphere, and towering loops, plumes and holes in the corona. These give the Sun its sparkle, from time to time culminating in the fireworks set off by flares and coronal mass ejections. This talk will provide a very personal selection of aspects of the structure and evolution of the solar magnetic field, how it shapes the Sun’s atmosphere and makes the Sun variable and active and how this variability and activity compares with those of other stars.

Speaker: Sami K. Solanki (Max-Planck-Institut für Sonnensystemforschung (MPS), Göttingen, Germany) and School of Space Research, Kyung Hee University, Yongin, Republic of Korea)

Conference dinner

Friday 13 September

Diagnostic tools and numerical methods in solar physics

Convener: Jasmina Magdalenic (KU Leuven)

69 Why use real-time operational data in Solar Physics and Space Weather research?

The Solar Influences Data Analysis Center (SIDC) at the Royal Observatory of Belgium (ROB) is well known for its advanced solar data analysis methods and comprehensive data catalogues, including CACTUS for automatic CME detection, Solar Demon for EUV flare and dimming detection, SPoCA-suite for the extraction of active regions and coronal holes, etc. Beyond its research initiatives and data processing capabilities, SIDC is also deeply engaged in operational activities related to space weather, ground-based and space-based instrumentation and observations.

This presentation aims to illustrate how real-time operational data collected and analyzed by forecasters serves as a valuable resource for researchers. It will highlight the importance of integrating this data into research workflows and demonstrate how such integration can lead to significant advancements in both solar physics research and space weather forecasting. Finally, from an operational perspective, we will pinpoint areas where real-time models perform poorly, highlighting opportunities for further exploration to improve our knowledge of solar physics and enhance forecasting models.

Speaker: Judith de Patoul (Solar-Terrestrial Centre of Excellence - SIDC, Royal Observatory of Belgium)

Space weather and the solar-heliospheric connections

Convener: Jasmina Magdalenic (KU Leuven)

70 Solar wind, space weather and solar-terrestrial connection

This review talk covers the solar-terrestrial connection, especially from the perspective of space weather modelling and forecasting.

Firstly, we give an overview of the effects of space weather and provide examples of their economic, political, and societal costs. This is followed up by a review of the current state-of-the-art operational space weather forecasting and nowcasting tools, such as the portal of ESA’s SSA, the European VSWMC, NOAA’s SWPC and NASA's CCMC and the wide variety of models included in them. The three categories of space weather effects, i.e., geomagnetic storms, radiation storms and radio blackouts, will be analysed separately.

Next, we discuss the new developments in the field, such as full 3D global coronal models and advanced CME geometries, and how these could contribute to improving understanding and forecasting space weather.

We conclude the review talk by elaborating on the current biggest challenges and uncertainties in this modelling (including the time-dependency of the solar wind, effects of the smaller scales, coronal heating, and uncertainties in the observations that bound our models) and how these could possibly be tackled.

It is also emphasized that while the research-to-operations link is fairly well-established in our community, thanks to initiatives such as VSWMC, the return link is still limited. Better communication must be established with the end-users for feedback regarding i) how well the models perform in practice and ii) how to better design future models to fulfil the actual user needs.

Speaker: Michaela Brchnelova (KU Leuven)

Topic6_Contr70_Brchnelova.pdf

71 Predicting geo-effectiveness two days prior to CME impact with EUHFORIA

The EUropean Heliospheric FORecasting Information Asset (EUHFORIA, Pomoell and Poedts, 2018), a physics-based and data-driven heliospheric and CME propagation model, can predict the solar wind plasma and magnetic field conditions at Earth. It contains several flux-rope CME models, such as the simple spheromak and more advanced FRi3D and toroidal CME models. This enables the prediction of the sign and strength of the magnetic field components upon the arrival of the CME at Earth and, thus, the geo-effectiveness of the CME impact. EUHFORIA has been coupled to several global magnetosphere models like OpenGGCM, GUMICS-4, and Gorgon-Space. In addition, the synthetic data at L1 (from the EUHFORIA simulation) can be used as input for empirical models and neural networks to predict the geomagnetic indices like Disturbance-storm-time (Dst) or Kp that quantify the impact of the magnetized plasma encounters on Earth’s magnetosphere. Hence, we also coupled EUHFORIA to empirical models and machine learning based models to predict the geomagnetic indices. We then compare the results of these models to observational data to evaluate their performance in predicting the geo-effect indices. We obtain the input parameters for running the geomagnetic indices models two to three days in advance.

We perform ensemble modelling considering the L1 monitor precision in its orbit and the uncertainty in the initial CME parameters at launch for error quantification. This study validates various space weather forecasting model chains and checks the best compatibility and predictive capabilities using EUHFORIA data for operational space weather forecasting.

Speaker: Ms Anwesha Maharana (KU Leuven)

Predicting Geo-Effectiveness Two Days Prior to CME Impact with EUHFORIA

Topic6_Contr50_Maharana.pptx

72 Comparison of "homologous" solar eruptive events from two different solar rotations

With March 2022 we entered a new era of complex solar eruptions in the wake of solar cycle 25. Several of these so-called Big Solar Storms were observed in the past years in remote sensing image data and measured in-situ. Some of them even caused aurorae in low latitudes, repeatedly confirming that the interaction between multiple CMEs, as well as CIRs, lead to extreme conditions in near-Earth space. For the enhanced solar activity period at the end of 2023, we study a set of “homologous” eruptive events on the Sun. The two episodes of enhanced solar activity involve similar (active) regions and the same coronal hole but are separated by a full solar rotation. We point out the complexity for each set of events and aim to understand their similarities and differences as they arrive at Earth.

Speaker: Manuela Temmer (Institute of Physics)

Topic6_Contr64_Temmer[1].pdf

73 The Open Flux Problem: First steps with Solar Orbiter to investigate the underestimation of magnetic flux

The open flux problem is currently an unsolved mystery, representing a 2-3 factor mismatch between the open flux measured at 1 AU and that via remote sensing of the solar atmosphere and extrapolated to 1 AU. One explanation is that the open flux at the photosphere is underestimated, in particular in the polar regions. Until now it was impossible to test this with observations: the Polarimetric and Helioseismic Imager (PHI) on board Solar Orbiter has made this a reality such that in combination with Earth-based assets, such as SDO/HMI, stereoscopy can be employed.
First numerical simulations of the line-of-sight magnetic field centre-to-limb variation will be presented. This theoretical work suggests that the flux is indeed underestimated at all angles off disc centre, and is enhanced the lower the spatial resolution above μ = 0.5. Finally, preliminary stereoscopic analyses of the observed magnetic flux with both SO/PHI-HRT and SDO/HMI will be shown.

Speaker: Jonas Sinjan (Max Planck Institute for Solar System Research)

Topic6_Contr72_Sinjan.pptx

Coffee break and poster session 2

Space weather and the solar-heliospheric connections

Convener: Lucia Abbo (Istituto Nazionale di Astrofisica (INAF))

74 Exploring the connection between the Sun and the Heliosphere

One of the main goals of heliospheric physics is to gain a complete picture of the dynamic processes occurring in the solar atmosphere and how these influence the inner heliosphere. Missions such as ESA/NASA’s Solar Orbiter, which couples unprecedented, close-up views of the solar atmosphere to solar wind measurements in the inner heliosphere, provide invaluable insights into the sources, release and transport of the solar wind, coronal mass ejections, and solar energetic particles and their space weather impacts. In this review, I will highlight recent results from the latest missions on these topics and discuss what key questions still remain unanswered.

Speaker: Stephanie Yardley (Northumbria University)

Topic6_Contr158_SYardley.pptx

75 From multi-decadal to real-time solar wind modelling, connectivity and plasma signatures on and off the ecliptic plane

The solar wind streams from compact sources at or near the Sun, accelerates across the low solar corona, and expands into the whole interplanetary space. The physical properties of any wind streams thus reflect the characteristics of their source regions and those of the extended zones of the corona they cross, and are affected by the time-varying strength and geometry of the global background magnetic field. I will discuss 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. Similarly, I will relate magnetic connectivity jumps with solar wind plasma signatures, and discuss their occurrence frequency and amplitudes at different epochs of the solar cycle, on and off the ecliptic plane.
The same model constitutes the core of a forecasting tool (SWiFT-FORECAST, ESA SWESNET and Virtual Space Weather Modelling Centre), new aided by machine learning methods. Several validation and calibration schemes were introduced to select optimal subsets of the ensemble and to correct for model biases. I will address some of the main challenges related to the implementation and validation of such tools, 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.

Speaker: Rui Pinto (IRAP & InforMarty)

76 Reconstruction of CME-driven shocks detected by multi-spacecraft observations

Shocks driven by coronal mass ejections (CMEs) are the most relevant accelerators of solar energetic particles (SEPs) in the inner heliosphere. SEPs are of great scientific interest because they represent a natural hazard in the near-Earth environment, from the instruments on board spacecraft to the electricity networks and astronauts' lives. In this study, we aim at analyzing CME-driven shocks, possibly observed by multiple spacecraft. We use remote sensing observations from Stereo-A, SOHO, Parker Solar Probe and Solar Orbiter to analyse shock waves both in 2D and 3D and to determine their physical parameters, such as the compression ratio and the Mach numbers. Physical quantities estimated through remote-sensing observations can be compared with in-situ measurements from various instruments. Following the evolution of the parameters characterizing the CMEs from the source to space will help space weather models to improve predictions on the arrival of SEPs at the Earth. This study is achieved in the context of the research project “Data-based predictions of solar energetic particle arrival to the Earth: ensuring space data and technology integrity from hazardous solar activity events” funded by the Italian Ministry of Research under the grant scheme PRIN-2022-PNRR.

Speaker: Federica Chiappetta (Department of Physics, Università della Calabria)

Topic6_Contr225_Chiappetta.pptx

77 How changing of source surface height parameter in EUHFORIA affect solar wind simulations

A large discrepancy between modelling results and in-situ observations by Parker Solar Probe (PSP) was observed while modelling of solar wind using the 3D MHD model EUHFORIA (Pomoell & Poedts, 2018) at near the Sun distances. The default coronal model used in EUHFORIA consists of potential field source surface extrapolation (PFSS), Schatten current sheet (SCS) model and semi-empirical WSA model, which simulate plasma and magnetic conditions at inner boundary (0.1 AU). The outer boundary of PFSS model, known as source surface height parameter (RSS), and the inner boundary of SCS model are among the free parameters in the coronal model that determine the area of modelled coronal holes, which in turn influences the area of open flux. A default value of RSS = 2.6 R⊙ as suggested by McGregor et al. (2008) is used in solar wind modelling at short radial distances. It is reported that lower RSS value in coronal models better captures the area of coronal holes (Asvestari et al., 2019), reconstructs small-scale features (Badman et. al., 2020), and represents coronal magnetic field topologies during different phases of solar cycles (Lee et al. 2011; Arden et al. 2014).

In this study, we change RSS value and inner boundary of SCS model, while keeping default values for other parameters. We then compare the solar wind modelling results with modified RSS parameter to those obtained using all default parameters in the coronal model, by evaluating their agreement with the in situ observations from PSP for its first ten perihelion encounters.

Speaker: Dr Senthamizh Pavai Valliappan (Royal Observatory of Belgium)

Valliappan_ESPM_2024.pdf

78 Coronal magnetic field modeling using a non-spherical source surface: implications for the global structuring of the corona

Global models of the solar coronal magnetic field are an essential tool for assessing the global-scale magnetic environment of the corona and its connectivity to the heliosphere. In particular, the Potential Field Source Surface (PFSS) model continues to be a frequently and widely adopted tool in the community despite several well-known deficiencies of the model. For instance, regions of open magnetic field provided by the model often only superficially match the observed coronal holes at EUV wavelengths which has been posited as a possible significant source of error contributing to the limited accuracy of many solar wind prediction models. Recently, a different issue has been highlighted through near-Sun solar wind observations by Parker Solar Probe (PSP), as an accurate PFSS modeling of the solar wind magnetic field polarity has only been achieved for source surface radii typically considered to be excessively low.

In this work, we study whether relaxing the fundamental assumption of the PFSS model of a fixed spherical source surface beyond which the magnetic field is purely radial can alleviate the noted deficiencies of the model. To this aim, we employ magnetofrictional modeling to construct magnetic field models where the coronal magnetic field is selectively opened in regions corresponding to those of observed coronal holes. We compare the resulting model results not only to PFSS, global coronal magnetohydrodynamic modeling and imaging observations, but also contrast the results with PSP in-situ observations. Furthermore, we discuss the implications of the results on the unresolved issue of missing open flux.

Speaker: Dr Jens Pomoell (University of Helsinki)

Closing and final remarks

Conveners: Dr Alessandro Bemporad (Istituto Nazionale di Astrofisica (INAF)), Dr Istvan Ballai (University of Sheffield)