arXiv subjects

J. Magdalenic

Publications and source records attributed to J. Magdalenic.

17 recordsLinked to original sources

arXiv2026

Deformation of the CME and CME-driven shock due to interaction with the ambient solar wind: I. Modelling with Cone Model

Context. The near-Earth environment is continuously impacted by the solar wind and the transients embedded in it. The largest eruptions of plasma and magnetic field at the Sun are Coronal Mass Ejections (CMEs), which, upon reaching Earth, can induce geomagnetic storms and disrupt our technologically advanced societies. Aims. We aim to improve our understanding of how CMEs and CME-driven shock waves interact with the ambient solar wind, and how the resulting deformations in time and space affect the accuracy of space weather forecasting. Methods. We studied two Earth-directed CMEs, observed on December 7, 2020 and October 28, 2021. To model the solar wind and CME propagation in the inner heliosphere, we used the state-of-the-art 3D MHD model EUHFORIA with the cone CME model, focusing on the regions along the main direction of propagation (MDP) and along the Sun-Earth line. Results. The deformations of the CME and the CME-driven shock can be significant. Both CMEs propagate in a variable background wind and are structured differently even at very close angular distances. The first, in a mildly structured wind, shows its stronger deformation predominantly away from the MDP; the second, in a more complex environment, develops a strongly structured shock at very different locations, including regions close to the MDP. Conclusions. These interactions also affect the characteristics of the CME-driven shock, such as the gas compression ratio across it. CMEs observed as flank encounters at Earth can be strongly affected by the ambient solar wind, with the expected differences in the arrival time at Earth reaching up to 16 hours.

astro-ph.SR↗

arXiv2025

Observing the solar corona from a formation-flying mission. First results of Proba-3/ASPIICS

We report the first results from observations of the solar corona by the ASPIICS coronagraph aboard the Proba-3 mission. ASPIICS (Association of Spacecraft for Polarimetric and Imaging Investigation of the Corona of the Sun) is a giant coronagraph consisting of the telescope mounted aboard one of the mission's spacecraft and the external occulter placed on the second spacecraft. The two spacecraft separated by around 144 m fly in a precise formation up to 5.5 hours at a time, which allows coronal observations in eclipse-like conditions, i.e. close to the limb (typically down to 1.099 Rs, occasionally down to 1.05 Rs) and with very low straylight. ASPIICS observes quasi-stationary structures, such as coronal loops, streamers, quiescent prominences, and a variety of dynamic phenomena: erupting prominences, coronal mass ejections, jets, slow solar wind outflows, coronal inflows. In particular, weak, widespread and persistent small-scale outflows and inflows between 1.3 and 3 Rs are observed at a high spatial (5.6 arcsec) and temporal (30 s) resolution for the first time, expanding the range of scales at which the variable slow solar wind is observed to form.

astro-ph.SR↗

arXiv2025

The ASPIICS solar coronagraph aboard the Proba-3 formation flying mission. Scientific objectives and instrument design

We describe the scientific objectives and instrument design of the ASPIICS coronagraph launched aboard the Proba-3 mission of the European Space Agency (ESA) on 5 December 2024. Proba-3 consists of two spacecraft in a highly elliptical orbit around the Earth. One spacecraft carries the telescope, and the external occulter is mounted on the second spacecraft. The two spacecraft fly in a precise formation during 6 hours out of 19.63 hour orbit, together forming a giant solar coronagraph called ASPIICS (Association of Spacecraft for Polarimetric and Imaging Investigation of the Corona of the Sun). Very long distance between the external occulter and the telescope (around 144 m) represents an increase of two orders of magnitude compared to classical externally occulted solar coronagraphs. This allows us to observe the inner corona in eclipse-like conditions, i.e. close to the solar limb (down to 1.099 Rs) and with very low straylight. ASPIICS will provide a new perspective on the inner solar corona that will help solve several outstanding problems in solar physics, such as the origin of the slow solar wind and physical mechanism of coronal mass ejections.

astro-ph.SR↗

arXiv2025

On the source sizes of type II radio bursts with LOFAR

Solar radio bursts can provide important insights into the underlying physical mechanisms that drive the small and large-scale eruptions on the Sun. Since metric radio observations can give us direct observational access to the inner and middle corona, they are often used as an important tool to monitor and understand the coronal dynamics. While the sizes of the radio sources that can be observed in the solar corona is essential for understanding the nature of density turbulence within the solar corona and its subsequent influence on the angular broadening observed in radio source measurements, the smallest radio sources associated with solar radio bursts have so far been limited by observational techniques and the radio instrument's baselines. We selected three type II bursts that were observed with the LOFAR core and remote stations in the Solar Cycle 24. We estimated the sizes and shapes (ellipticity) of the radio sources between $20-200$ MHz using a two-dimensional Gaussian approximation. Our analysis shows that the smallest radio source size for type II bursts in the solar corona which can be observed in the solar atmosphere at low frequencies is $1.5^\prime \pm 0.5^\prime$ at 150 MHz. However, even though the observations were taken with remote baselines (with a maximum distance of $\sim 85~km$), the effective baselines were much shorter ($\sim 35~km$) likely due to snapshot imaging of the Sun. Our results show that the radio source sizes are less affected by scattering than suggested in previous studies. Our measurements indicate a smaller source sizes at frequencies below 95 MHz compared to previous reports, though some overlap exists with measurements at higher frequencies, using smaller baselines.

astro-ph.SR↗

arXiv2024

Validation of EUHFORIA cone and spheromak Coronal Mass Ejection Models

Aims. We present the validation results for arrival times and geomagnetic impact of Coronal Mass Ejections (CMEs), using the cone and spheromak CME models implemented in EUropean Heliospheric FORecasting Information Asset (EUHFORIA). Validating numerical models is crucial in ensuring their accuracy and performance with respect to real data. Methods. We compare CME plasma and magnetic field signatures, measured in situ by satellites at the L1 point, with the simulation output of EUHFORIA. The validation of this model was carried out by using two datasets in order to ensure a comprehensive evaluation. The first dataset focuses on 16 CMEs that arrived at the Earth, offering specific insights into the model's accuracy in predicting arrival time and geomagnetic impact. Meanwhile, the second dataset encompasses all CMEs observed over eight months within Solar Cycle 24, regardless of whether they arrived at Earth, covering periods of both solar minimum and maximum activity. This second dataset enables a more comprehensive evaluation of the model's predictive precision in term of CME arrivals and misses. Results. Our results show that EUHFORIA provides good estimates in terms of arrival times, with root mean square errors (RMSE) values of 9 hours. Regarding the number of correctly predicted ICME arrivals and misses, we find a 75% probability of detection in a 12 hours time window and 100% probability of detection in a 24 hours time window. The geomagnetic impact forecasts, measured by the $K_p$ index, provide different degrees of accuracy, ranging from 31% to 69%. These results validate the use of cone and spheromak CMEs for real-time space weather forecasting.

astro-ph.SR↗

arXiv2023

Validation of heliospheric modeling algorithms through pulsar observations II: simulations with EUHFORIA

In space weather studies and forecasting we employ magnetohydrodynamic (MHD) simulations which can provide rather accurate reconstruction of the solar wind dynamics and its evolution. However, all MHD simulations are restricted by the input data and the modelled solar wind characteristics need to be validated with different types of observations. That is very difficult, in particular for the solar wind characteristics close to the Sun, since the majority of in-situ observations are taken in the vicinity of the Earth. This is why all alternative methods for estimation of solar wind plasma characteristics are very important. In this study we utilise low radio frequency observations of pulsars to probe the total electron content along the line of sight. For the first time, we compare density estimates from pulsars with predictions from the 3D MHD modelling code; the EUropean Heliospheric FORecasting Information Asset (EUHFORIA). We find a very good correlation for the solar wind density along a given line of sight obtained by EUHFORIA and pulsar observations. We also demonstrate that the pulsar observations can be very useful not only for the model validation but also for understanding its limitations.

astro-ph.SR↗

arXiv2022

Prominence eruption observed in He II 304 Å up to $>6 R_\sun$ by EUI/FSI aboard Solar Orbiter

We report observations of a unique, large prominence eruption that was observed in the He II 304 Å passband of the the Extreme Ultraviolet Imager/Full Sun Imager telescope aboard Solar Orbiter on 15-16 February 2022. Observations from several vantage points (Solar Orbiter, the Solar-Terrestrial Relations Observatory, the Solar and Heliospheric Observatory, and Earth-orbiting satellites) were used to measure the kinematics of the erupting prominence and the associated coronal mass ejection. Three-dimensional reconstruction was used to calculate the deprojected positions and speeds of different parts of the prominence. Observations in several passbands allowed us to analyse the radiative properties of the erupting prominence. The leading parts of the erupting prominence and the leading edge of the corresponding coronal mass ejection propagate at speeds of around 1700 km/s and 2200 km/s, respectively, while the trailing parts of the prominence are significantly slower (around 500 km/s). Parts of the prominence are tracked up to heights of over $6 R_\sun$. The He II emission is probably produced via collisional excitation rather than scattering. Surprisingly, the brightness of a trailing feature increases with height. The reported prominence is the first observed in He II 304 Å emission at such a great height (above 6 $R_\sun$).

astro-ph.SR↗

arXiv2021

Modelling a multi-spacecraft coronal mass ejection encounter with EUHFORIA

Coronal mass ejections (CMEs) are a manifestation of the Sun's eruptive nature. They can have a great impact on Earth, but also on human activity in space and on the ground. Therefore, modelling their evolution as they propagate through interplanetary space is essential. EUropean Heliospheric FORecasting Information Asset (EUHFORIA) is a data-driven, physics-based model, tracing the evolution of CMEs through background solar wind conditions. It employs a spheromak flux rope, which provides it with the advantage of reconstructing the internal magnetic field configuration of CMEs. This is something that is not included in the simpler cone CME model used so far for space weather forecasting. This work aims at assessing the spheromak CME model included in EUHFORIA. We employed the spheromak CME model to reconstruct a well observed CME and compare model output to in situ observations. We focus on an eruption from 6 January 2013 encountered by two radially aligned spacecraft, Venus Express and STEREO-A. We first analysed the observed properties of the source of this CME eruption and we extracted the CME properties as it lifted off from the Sun. Using this information, we set up EUHFORIA runs to model the event. The model predicts arrival times from half to a full day ahead of the in situ observed ones, but within errors established from similar studies. In the modelling domain, the CME appears to be propagating primarily southward, which is in accordance with white-light images of the CME eruption close to the Sun. In order to get the observed magnetic field topology, we aimed at selecting a spheromak rotation angle for which the axis of symmetry of the spheromak is perpendicular to the direction of the polarity inversion line (PIL). The modelled magnetic field profiles, their amplitude, arrival times, and sheath region length are all affected by the choice of radius of the modelled spheromak.

astro-ph.SR↗

arXiv2021

LOFAR imaging of the solar corona during the 2015 March 20 solar eclipse

The solar corona is a highly-structured plasma which can reach temperatures of more than ~2 MK. At low frequencies (decimetric and metric wavelengths), scattering and refraction of electromagnetic waves are thought to considerably increase the imaged radio source sizes (up to a few arcminutes). However, exactly how source size relates to scattering due to turbulence is still subject to investigation. The theoretical predictions relating source broadening to propagation effects have not been fully confirmed by observations due to the rarity of high spatial resolution observations of the solar corona at low frequencies. Here, the LOw Frequency ARray (LOFAR) was used to observe the solar corona at 120-180 MHz using baselines of up to ~3.5 km (corresponding to a resolution of ~1-2') during the partial solar eclipse of 2015 March 20. A lunar de-occultation technique was used to achieve higher spatial resolution (~0.6') than that attainable via standard interferometric imaging (~2.4'). This provides a means of studying the contribution of scattering to apparent source size broadening. It was found that the de-occultation technique reveals a more structured quiet corona that is not resolved from standard imaging, implying scattering may be overestimated in this region when using standard imaging techniques. However, an active region source was measured to be ~4' using both de-occultation and standard imaging. This may be explained by the increased scattering of radio waves by turbulent density fluctuations in active regions, which is more severe than in the quiet Sun.

astro-ph.SR↗

arXiv2019

Testing the background solar wind modelled by EUHFORIA

In order to address the growing need for more accurate space weather predictions, a new model named EUHFORIA (EUropean Heliospheric FORecasting Information Asset) was recently developed (Pomoell and Poedts, 2018). We present first results of the performance assessment for the solar wind modeling with EUHFORIA and identify possible limitations of its present setup. Using the basic EUHFORIA 1.0.4. model setup with the default input parameters, we modeled background solar wind (no coronal mass ejections) and compared the obtained results with ACE, in situ measurements. For the need of statistical study we developed a technique of combining daily EUHFORIA runs into continuous time series. The combined time series were derived for the years 2008 (low solar activity) and 2012 (high solar activity) from which in situ speed and density profiles were extracted. We find for the low activity phase a better match between model results and observations compared to the considered high activity time interval. The quality of the modeled solar wind parameters is found to be rather variable. Therefore, to better understand the obtained results we also qualitatively inspected characteristics of coronal holes, sources of the studied fast streams. We discuss how different characteristics of the coronal holes and input parameters to EUHFORIA influence the modeled fast solar wind, and suggest possibilities for the improvements of the model.

astro-ph.SR↗

arXiv2018

Shock location and CME 3D reconstruction of a solar type II radio burst with LOFAR

Type II radio bursts are evidence of shocks in the solar atmosphere and inner heliosphere that emit radio waves ranging from sub-meter to kilometer lengths. These shocks may be associated with CMEs and reach speeds higher than the local magnetosonic speed. Radio imaging of decameter wavelengths (20-90 MHz) is now possible with LOFAR, opening a new radio window in which to study coronal shocks that leave the inner solar corona and enter the interplanetary medium and to understand their association with CMEs. To this end, we study a coronal shock associated with a CME and type II radio burst to determine the locations at which the radio emission is generated, and we investigate the origin of the band-splitting phenomenon.

astro-ph.SR↗

arXiv2018

LOFAR observations of the quiet solar corona

The quiet solar corona emits meter-wave thermal bremsstrahlung. Coronal radio emission can only propagate above that radius, $R_ω$, where the local plasma frequency eqals the observing frequency. The radio interferometer LOw Frequency ARray (LOFAR) observes in its low band (10 -- 90 MHz) solar radio emission originating from the middle and upper corona. We present the first solar aperture synthesis imaging observations in the low band of LOFAR in 12 frequencies each separated by 5 MHz. From each of these radio maps we infer $R_ω$, and a scale height temperature, $T$. These results can be combined into coronal density and temperature profiles. We derived radial intensity profiles from the radio images. We focus on polar directions with simpler, radial magnetic field structure. Intensity profiles were modeled by ray-tracing simulations, following wave paths through the refractive solar corona, and including free-free emission and absorption. We fitted model profiles to observations with $R_ω$ and $T$ as fitting parameters. In the low corona, $R_ω< 1.5$ solar radii, we find high scale height temperatures up to 2.2e6 K, much more than the brightness temperatures usually found there. But if all $R_ω$ values are combined into a density profile, this profile can be fitted by a hydrostatic model with the same temperature, thereby confirming this with two independent methods. The density profile deviates from the hydrostatic model above 1.5 solar radii, indicating the transition into the solar wind. These results demonstrate what information can be gleaned from solar low-frequency radio images. The scale height temperatures we find are not only higher than brightness temperatures, but also than temperatures derived from coronograph or EUV data. Future observations will provide continuous frequency coverage, eliminating the need for local hydrostatic density models.

astro-ph.SR↗

arXiv2017

The Association of a J-burst with a Solar Jet

Context. The Sun is an active star that produces large-scale energetic events such as solar flares and coronal mass ejections and numerous smaller-scale events such as solar jets. These events are often associated with accelerated particles that can cause emission at radio wavelengths. The reconfiguration of the solar magnetic field in the corona is believed to be the cause of the majority of solar energetic events and accelerated particles. Aims. Here, we investigate a bright J-burst that was associated with a solar jet and the possible emission mechanism causing these two phenomena. Methods. We used data from the Solar Dynamics Observatory (SDO) to observe a solar jet, and radio data from the Low Frequency Array (LOFAR) and the Nançay Radioheliograph (NRH) to observe a J-burst over a broad frequency range (33-173 MHz) on 9 July 2013 at ~11:06 UT. Results. The J-burst showed fundamental and harmonic components and it was associated with a solar jet observed at extreme ultraviolet wavelengths with SDO. The solar jet occurred at a time and location coincident with the radio burst, in the northern hemisphere, and not inside a group of complex active regions in the southern hemisphere. The jet occurred in the negative polarity region of an area of bipolar plage. Newly emerged positive flux in this region appeared to be the trigger of the jet. Conclusions. Magnetic reconnection between the overlying coronal field lines and the newly emerged positive field lines is most likely the cause of the solar jet. Radio imaging provides a clear association between the jet and the J-burst which shows the path of the accelerated electrons.

astro-ph.SR↗

arXiv2015

LOFAR tied-array imaging and spectroscopy of solar S bursts

Context. The Sun is an active source of radio emission that is often associated with energetic phenomena ranging from nanoflares to coronal mass ejections (CMEs). At low radio frequencies (<100 MHz), numerous millisecond duration radio bursts have been reported, such as radio spikes or solar S bursts (where S stands for short). To date, these have neither been studied extensively nor imaged because of the instrumental limitations of previous radio telescopes. Aims. Here, Low Frequency Array (LOFAR) observations were used to study the spectral and spatial characteristics of a multitude of S bursts, as well as their origin and possible emission mechanisms. Methods. We used 170 simultaneous tied-array beams for spectroscopy and imaging of S bursts. Since S bursts have short timescales and fine frequency structures, high cadence (~50 ms) tied-array images were used instead of standard interferometric imaging, that is currently limited to one image per second. Results. On 9 July 2013, over 3000 S bursts were observed over a time period of ~8 hours. S bursts were found to appear as groups of short-lived (<1 s) and narrow-bandwidth (~2.5 MHz) features, the majority drifting at ~3.5 MHz/s and a wide range of circular polarisation degrees (2-8 times more polarised than the accompanying Type III bursts). Extrapolation of the photospheric magnetic field using the potential field source surface (PFSS) model suggests that S bursts are associated with a trans-equatorial loop system that connects an active region in the southern hemisphere to a bipolar region of plage in the northern hemisphere. Conclusions. We have identified polarised, short-lived solar radio bursts that have never been imaged before. They are observed at a height and frequency range where plasma emission is the dominant emission mechanism, however they possess some of the characteristics of electron-cyclotron maser emission.

astro-ph.SR↗

arXiv2009

Analysis of a global Moreton wave observed on October 28, 2003

We study the well pronounced Moreton wave that occurred in as- sociation with the X17.2 are/CME event of October 28, 2003. This Moreton wave is striking for its global propagation and two separate wave centers, which implies that two waves were launched simultane- ously. The mean velocity of the Moreton wave, tracked within different sectors of propagation direction, lies in the range of v ~ 900-1100 km/s with two sectors showing wave deceleration. The perturbation profile analysis of the wave indicates amplitude growth followed by amplitude weakening and broadening of the perturbation profile, which is con- sistent with a disturbance first driven and then evolving into a freely propagating wave. The EIT wavefront is found to lie on the same kinematical curve as the Moreton wavefronts indicating that both are different signatures of the same physical process. Bipolar coronal dim- mings are observed on the same opposite East-West edges of the active region as the Moreton wave ignition centers. The radio type II source, which is co-spatially located with the first wave front, indicates that the wave was launched from an extended source region (& 60 Mm). These findings suggest that the Moreton wave is initiated by the CME expanding flanks.

astro-ph.SR↗

arXiv2002

The Neupert effect in solar flares and implications for coronal heating

Based on simultaneous observations of solar flares in hard and soft X-rays we studied several aspects of the Neupert effect. About half of 1114 analyzed events show a timing behavior consistent with the Neupert effect. For these events, a high correlation between the soft X-ray peak flux and the hard X-ray fluence is obtained, being indicative of electron-beam-driven evaporation. However, for about one fourth of the events there is strong evidence for an additional heating agent other than electron beams. We discuss the relevance of these findings with respect to Parker's idea of coronal heating by nanoflares.

astro-ph↗

arXiv2002

Investigation of the Neupert effect in solar flares. I. Statistical properties and the evaporation model

Based on a sample of 1114 flares observed simultaneously in hard X-rays (HXR) by the BATSE instrument and in soft X-rays (SXR) by GOES, we studied several aspects of the Neupert effect and its interpretation in the frame of the electron-beam-driven evaporation model. In particular, we investigated the time differences ($Δt$) between the maximum of the SXR emission and the end of the HXR emission, which are expected to occur at almost the same time. Furthermore, we performed a detailed analysis of the SXR peak flux -- HXR fluence relationship for the complete set of events, as well as separately for subsets of events which are likely compatible/incompatibe with the timing expectations of the Neupert effect. The distribution of the time differences reveals a pronounced peak at $Δt = 0$. About half of the events show a timing behavior which can be considered to be consistent with the expectations from the Neupert effect. For these events, a high correlation between the SXR peak flux and the HXR fluence is obtained, indicative of electron-beam-driven evaporation. However, there is also a significant fraction of flares (about one fourth), which show strong deviations from $Δt = 0$, with a prolonged increase of the SXR emission distinctly beyond the end of the HXR emission. These results suggest that electron-beam-driven evaporation plays an important role in solar flares. Yet, in a significant fraction of events, there is also clear evidence for the presence of an additional energy transport mechanism other than the nonthermal electron beams, where the relative contribution is found to vary with the flare importance.

astro-ph↗