Astrophysical simulations require trade-offs between compute time and physical accuracy. This frequently includes targeting certain physical scales at the expense of others. Simulations investigating solar coronal heating and solar wind acceleration usually select either high resolution for a small domain or low resolution for a global domain. Bridging this gap requires linking structures present on the solar surface to both the middle corona (approximately 1.5 - 6 solar radii) and the solar wind. In this work we analyze three simulations of the global solar corona that vary the resolution of the surface boundary condition while keeping the same parameterization of a thermodynamic, wave-turbulence-driven magnetohydrodynamic model. We quantify structural differences endemic to each simulation using spherical harmonic decomposition and associated statistics. We use this information to examine how surface resolution influences heating and magnetic complexity in the corona and solar wind and the subsequent impacts on density, temperature, and flow structure. In principle, this can enable more efficient subgrid modeling in future low resolution simulations.

How to cite: Evans, C., Downs, C., Schmit, D., and Crowley, J.: Quantifying how surface complexity influences properties of the solar corona and solar wind, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1196, https://doi.org/10.5194/egusphere-egu24-1196, 2024.

To forecast the solar wind arriving at Earth in advance, and hence its impacts on technology, it is important to have a good understanding of how the solar wind is generated by the solar corona. Helium is a major constituent of the corona/solar wind that plays an important role in the energy budget of the corona and the acceleration of the solar wind. Helium abundance varies significantly with the solar cycle and in the different types of fast and slow solar winds. We present the newly-developed multi-species IRAP Solar Atmospheric Model (ISAM) which solves for the coupled transport of both neutral and charged particles between the chromosphere and the corona, including a self-consistent treatment of collisional and ionisation processes. We exploit ISAM to study the mechanisms that regulate Helium abundance in the source region of the fast and slow solar winds and contrast numerical results with and without Helium included in the model. We compare our model outputs with as many observations as possible, including Helios, Parker Solar Probe and Solar Orbiter data, in particular from the Proton and Alpha particle Sensor, SWA-PAS. We show that our simulations are in good agreement with previous studies, in particular that the solar cycle variation in Helium abundance can be explained by differences in abundance found for each solar wind type by ISAM, when just using diffusion in the model and not (yet) including the ponderomotive force. 

How to cite: Thomas, S., Rouillard, A., Lomazzi, P., Poirier, N., and Blelly, P.-L.: Simulating Differences in Helium Abundances between Fast and Slow Solar Winds, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3962, https://doi.org/10.5194/egusphere-egu24-3962, 2024.

The solar wind variations during a solar cycle are critical in understanding the solar wind acceleration mechanism in different phases of the solar cycle. It is also important in predicting the solar wind distribution in the heliosphere. This problem has been investigated from different aspects, from data analysis to numerical modeling. Previous observations have shown that the distribution of fast and slow wind are different between solar minimum and maximum. In this study, we study the solar wind variations based on a first-principles model, the Alfven Wave Solar atmosphere Model (AWSoM) developed at the University of Michigan. Huang et al. (2023) have used the ADAPT-GONG magnetograms in the last solar cycle to drive the solar wind model and shown that one of the input parameters of the model, the Poynting flux parameter, can be empirically predicted with the open field area. Moreover, they suggested that the average energy deposition rate in the open field regions is approximately constant during a solar cycle. In this study, we use the GONG synoptic magnetograms, and determine if similar conclusions are also valid. We also systematically compare the model performance between the two different input magnetograms.

How to cite: Huang, Z., Toth, G., Sachdeva, N., and van der Holst, B.: The solar wind in the last solar cycle driven by ADAPT-GONG and GONG magnetograms, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6743, https://doi.org/10.5194/egusphere-egu24-6743, 2024.

When solar wind plasma propagates outward, the electron density decreases rapidly with solar distance, and charge states of heavy ions freeze in at 1 to 5 solar radii. Thus, charge states of heavy ions carry important information about the temperature profile in the lower corona. Oxygen and Iron ions are the most abundant heavy ions in the solar wind, and their data quality is relatively higher than that of other heavy ion species.Statistically, the averaged charge states of O and Fe in the solar wind usually maintain a weak positive correlation, sometimes exhibiting a strong positive correlation in solar wind associated with Coronal Mass Ejections (CMEs). The averaged charge states of O and Fe also correlate with solar wind speed and the solar cycle.

In this study, we use ten years of in-situ solar wind Oxygen and Iron ion data obtained from the Solar Wind Ion Composition Spectrometer (SWICS) aboard the Advanced Composition Explorer (ACE). The data set is derived from Pulse Height Analysis (PHA) data, ensuring high time resolution (12 minutes).

We identify around one hundred structures (time periods) where the averaged charge states of Fe and O exhibit significant anti-correlations (Spearman rank correlation coefficient lower than -0.5). These structures have distinct signatures. We analyze the time scales of these structures, the magnitudes of the averaged charge state variations for O and Fe, the temporal lags between the onset and end of those variations , the distribution of structures in the solar wind (e.g., whether they are associated with Interplanetary Coronal Mass Ejections (ICMEs) and their relative position within ICMEs), and their distribution in the solar cycle.

Compared to more widely occurring positive correlation structures, anti-correlation structures are rarer and more interesting, reflecting the complex variations in the radial temperature profile and electron density profile of the lower corona. Large-scale anti-correlation structures suggest the presence of a relatively stable radial energy transfer process within 1 to 5 solar radii.

How to cite: Gu, C., Heidrich-Meisner, V., and Wimmer-Schweingruber, R. F.: Report on In Situ Observations of the Anti-Correlated Variations in Freeze-in Temperatures of Heavy Ions in the Solar Wind, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12235, https://doi.org/10.5194/egusphere-egu24-12235, 2024.

The goal of this study is to narrow down the uncertainties global modeling and PFSS back-tracing introduces when source regions are identified for in-situ data collections. We use the Space Weather Modeling Framework's Multi-Ion Alfven Wave Solar atmosphere Model with non-equilibrium ionization of heavy ions (NEI) to connect the remote sensing and in-situ signatures of solar wind properties from formation into the heliosphere. We use the NEI resulting charge state distributions and in-situ plasma properties to identify and connect source regions and their relating spectral emission signatures. The advantage of 3D modeling is that it enables data decomposition along the line-of-sight and study the effect of individual processes that result in the synthetic and actual observables. 

How to cite: Szente, J., Landi, E., and van der Holst, B.: Global Modeling of Heavy Ions in the Solar Corona and Inner Heliosphere with Multi-Ion-AWSoM, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6603, https://doi.org/10.5194/egusphere-egu24-6603, 2024.

As the solar wind streams propagate with different speeds through the interplanetary space, they meet and interact. This leads to the formation of large interaction regions, one of which is the rarefaction regions (RRs). RRs develop at the trailing edge of the fast solar wind stream and come from an area of small longitudinal extent on the Sun. They exhibit a fine and complex structure, and the stream interface position is usually unclear. Superposed epoch analysis of the proton and alpha parameters for different regions within RRs reveals gradual transitions in many of them. Moreover, majority of our observations show that most of the RR plasma parameters correspond to the fast solar wind characteristics, only the alpha-proton drift velocity decreases from the beginning of RR. We investigate different ways of its reduction in the interplanetary space and show that this feature is likely associated with the mirroring of the multi-component solar wind. We identify the composition boundary where the alpha relative abundance and alpha-proton temperature ratio change abruptly from the values typical for the fast wind toward slow wind values. We suggest that this boundary is the most probable candidate for the stream interface. Based on these findings, we speculate that the RR formation occurs near the Sun and formulate two possible scenarios.

How to cite: Ďurovcová, T., Šafránková, J., and Němeček, Z.: How the structure of rarefaction regions develops?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4309, https://doi.org/10.5194/egusphere-egu24-4309, 2024.

We investigate the evolution of  spatial distribution of solar wind sources by means of an extended time series of data-driven 3D simulations that cover solar 2 activity cycles. We examine the corresponding solar wind acceleration profiles as a function of source latitude and time, and highlight consequences for the interpretation of Parker Solar Probe (PSP) and Solar Orbiter (SolO) in-situ measurements. We 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.
We also indicate impacts on the rotation profile of the solar corona and on the occurrence of regions of enhanced poloidal and toroidal flow shear that can drive plasma instabilities.  Finally, we search for and test geometrical parameters alternative to the standard ones currently used in semi-empirical solar wind forecasting methods.

How to cite: Pinto, R., Rouillard, A., and Indurain, M.: Solar wind flows across the solar activity cycle, connectivity and plasma signatures on and off the ecliptic plane, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13385, https://doi.org/10.5194/egusphere-egu24-13385, 2024.

Coronal holes (CHs) have long been known as one of the main sources of high-speed solar wind streams, but recent evidence suggests that active regions (ARs) also play a significant role as solar wind sources. In this study, we aim to investigate the impact of both CHs and ARs as source regions of the solar wind. Both structures can be identified in extreme ultra-violet (EUV) solar images several days before they become geoeffective. We exploit this relation to construct a model that forecasts the solar wind speed at L1. First, we accurately detect and track the evolution of CHs and ARs over time by employing a segmentation algorithm on solar images. Next, we extract features from the indicated regions in EUV images and magnetograms, such as area and location of the source regions and the corresponding magnetic field configurations. These features, along with solar wind data from previous solar rotations and the current state of the solar cycle, are assimilated over time in a data-driven model that predicts the hourly solar wind speed at L1 four days in advance. During model training, we particularly focus on preserving the distribution of observed solar wind speeds to overcome a common drawback of data-driven solar wind speed prediction models, namely the underprediction of the peak values of solar storms. By adding a suitable regularization to the loss function, we force our model to follow the physical behavior more closely, which results in a significantly improved accuracy for predicting solar storms. Finally, we use our model to draw conclusions about the physical relevance of CHs and ARs for solar wind speed models. The model's performance is evaluated through cross-validation on 14 years of data and compared to other state-of-the-art models.

How to cite: Collin, D., Shprits, Y., Bianco, S., Inceoglu, F., Hofmeister, S., and Gallego, G.: Forecasting solar wind speed from coronal holes and active regions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18676, https://doi.org/10.5194/egusphere-egu24-18676, 2024.

The nonlinear evolution of Alfvén waves in the solar corona leads to the generation of Alfvénic turbulence. This description of the Alfvén waves involves parametric instabilities where the parent wave decays into slow mode waves giving rise to density fluctuations. These density fluctuations, in turn, play a crucial role in the modulation of the dynamic spectrum of type III radio bursts, which are observed at the fundamental of local plasma frequency and are sensitive to the local density. During observations of such radio bursts, fine structures are detected across different temporal ranges. In this study, we examine density fluctuations generated through the parametric decay instability (PDI) of Alfvén waves as a mechanism to generate striations in the dynamic spectrum of type III radio bursts using magnetohydrodynamic simulations of the solar corona. An Alfvén wave is injected into the quiet solar wind by perturbing the transverse magnetic field and velocity components, which subsequently undergo the PDI instability. The type III burst is modeled as a fast-moving radiation source that samples the background solar wind as it propagates to emit radio waves. We find the simulated dynamic spectrum to contain striations directly affected by the multiscale density fluctuations in the wind.

How to cite: Sishtla, C., Jebaraj, I., Pomoell, J., Magyar, N., Pulupa, M., Kilpua, E., and Bale, S.: The Effect of the Parametric Decay Instability on the Morphology of Coronal Type III Radio Bursts, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3450, https://doi.org/10.5194/egusphere-egu24-3450, 2024.

Detailed interferometric radio observations of solar activity allow us to constrain the dynamics of high-energy electron beams accelerated in flares and coronal mass ejections (CME). We have studied in detail the small-scale solar radio bursts, which accompanied one of the three homologous solar eruptions that originated from the western solar limb on November 04, 2015. We have used interferometric observations from the Murchison Widefield Array to image the multi-frequency emission in several radio channels between 80 and 300 MHz with 1-second resolution and 20 arcsec-pixels. The event began with a strong type II radio burst, and was followed by a separation of the emission into stationary and moving sources, the latter clearly related to the propagating CME structure. The observations show simultaneous multi-frequency flickering of intensity along a persistent off-limb structure related to the CME-driven shock wave, connecting the stationary and moving sources. This flickering emission persisted for more than 30 minutes. We present an analysis of its dynamics, its relation to the CME flux rope, the expected magnetic configurations, and electron beam properties. These observations provide valuable information about the evolution and kinematics of the CME in its early stages. 

How to cite: Kozarev, K.: Dynamics of Persistent Low-Frequency Radio Pulsations During the November 04, 2015 CME, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18797, https://doi.org/10.5194/egusphere-egu24-18797, 2024.

Coronal Mass Ejections (CMEs), and ever-changing solar wind conditions, drive processes in the Earth’s space-environment (the magnetosphere and ionosphere) which can strongly affect satellite communications, navigation systems, and power grids upon which society relies. Mitigation strategies are heavily dependent on accurate forecasting of the likely impact of space-weather conditions on operations. The tracking of plasma structures, and turbulence within, in the inner-heliosphere is now made possible by the LOw Frequency ARray (LOFAR, the world’s largest low-frequency radio-telescope) through observations of the scintillation of radio waves from astronomical sources propagating through these plasma structures. Information obtained through LOFAR can be augmented with in situ measurements from existing missions and the planned ESA Vigil mission to be stationed at L5, as well as other remote-sensing techniques, to provide an unprecedented advance warning of space weather detrimental to society. The Radio Investigations for Space Environment Research (RISER) project will provide a comprehensive understanding of the Earth’s space-environment through the use of novel radio observations and modelling techniques to investigate coupling between solar-driven inner-heliospheric structures and the Earth.

RISER will address the following key questions in the space-weather domain:

• How can we better attribute magnetospheric-ionospheric response to inner-heliospheric variability?

• How well can we establish a direct connection between parameters that characterise structures in the inner-heliosphere with the geo-effectiveness of geomagnetic disturbances?

• How can we identify and track plasma structures in the inner-heliosphere using scintillation data from low-frequency radio telescopes in a systematic way before they reach Earth?

• What is the value of improved forecasts of adverse space weather conditions when using radio-telescope observations and enhanced science of the inner heliosphere- magnetosphere-ionosphere system?

   

  Here, we give an overview of RISER, its high-level objectives, the importance and relevance to advancing our understanding of space-weather science and impacts, as well as a brief overview of the LOFAR-UK upgrades.

How to cite: Barnes, D., Bisi, M., Fallows, R., Forte, B., Milan, S., Jackson, D., Jackson, B., Odstrcil, D., and Chang, O.: Radio Investigations for Space Environment Research (RISER): An Overview, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19133, https://doi.org/10.5194/egusphere-egu24-19133, 2024.

The Sun is a subject to vivid research due to its significant impact on our daily existence. We know about the periodic behaviour in the structure of the Sun, the 11-year solar cycle, but we have yet to fully understand what it means for the inner heliosphere and how it affects the solar wind. Accurately modelling these structural changes in the solar Corona on large time scales is important to understand and even predict solar weather patterns that could potentially influence Earth's magnetic field, telecommunications, and even space missions. Fully comprehending these changes is crucial for enhancing our ability to forecast and prepare for potential solar events that might affect various aspects of our technological infrastructure and space exploration endeavours. 

To this end, we have prepared a database of solar corona and inner heliosphere simulations with the Space Weather Modeling Framework’s Alfvén Wave Solar atmosphere Model (SWMF/AWSoM) during Solar Cycles 24 and 25. Using SolarSoft’s FORWARD we study the distribution and emission of solar wind origins, such as coronal holes and active regions, throughout the solar cycles and analyse how well AWSoM is reproducing them at different phases of the solar cycle. We also compare how 1AU in-situ plasma measurements are predicted and how it relates to the reproduction of the origin of the solar wind in the corona.  

Studying the reproducibility of the coronal and heliospheric plasma throughout decades of time can prove invaluable in understanding changes in the solar structure during a solar cycle and benchmark the accuracy of the models’ predictive power in the future. 

How to cite: Koban, G., Szente, J., and van der Holst, B.: Studying the Long-Term Variability of the Solar Corona Using Modeling and Remote-Sensing Observations , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12058, https://doi.org/10.5194/egusphere-egu24-12058, 2024.

Radio emissions have a wide exploitation potential both in the remote diagnosis of their plasma sources, often impossible to explore in-situ, but also in the context of space weather for developing realistic forecasting models for the effects of energetic solar events, such as coronal plasma ejections (CMEs) on modern technologies on ground and in space. Here we discuss the importance of first-principle radiative models, not only for these applications but especially for developing realistic models for type-II and type-III radio emissions whose plasma sources are likely to be explored in situ by different satellites and spacecraft. At this early stage, first-principle radiative models combine a fundamental kinetic theory for describing wave instabilities in plasma sources, with numerical simulations of their saturation by nonlinear processes that generate free-propagating radio waves. We also discuss a series of further additions, in particular with nonlinear theories of the various wave-wave couplings responsible for the generation of radio emissions.

How to cite: Lazar, M., Lopez, R. A., Shaaban, S. M., and Poedts, S.: A plea for first-principles radiative models in solar energetic events, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12703, https://doi.org/10.5194/egusphere-egu24-12703, 2024.

Radio bursts from nearby active M-dwarfs have been frequently reported and extensively studied in solar or planetary paradigms. Whereas, their substructures or fine structures remain rarely explored despite their potential significance in diagnosing the plasma and magnetic field properties of the star. Such studies in the past have been limited by the sensitivity of radio telescopes. Here we report the inspiring results from the high time-resolution observations of a known flare star AD Leo with the Five-hundred-meter Aperture Spherical radio Telescope. We detected many radio bursts in the 2 days of observations with fine structures in the form of numerous millisecondscale sub-bursts. Sub-bursts on the first day display stripe-like shapes with nearly uniform frequency drift rates, which are possibly stellar analogs to Jovian S-bursts. Sub-bursts on the second day, however, reveal a different blob-like shape with random occurrence patterns and are akin to solar radio spikes. The new observational results suggest that the intense emission from AD Leo is driven by electron cyclotron maser instability, which may be related to stellar flares or interactions with a planetary companion.

How to cite: Zhang, J. and Tian, H.: Fine Structures of Radio Bursts from Flare Star AD Leo with FAST Observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1947, https://doi.org/10.5194/egusphere-egu24-1947, 2024.

It is now known that the fast solar wind streams originating from coronal holes can have a significant contribution to geomagnetic activity, particularly during periods of low solar activity. Moreover, coronal holes, many of which are long lived and overall time steady structures, have proven to be ideal hunting grounds for understanding the fast solar wind. In this regard, automated detection schemes are nowadays a standard approach for locating coronal holes in EUV images from the Solar Dynamics Observatory (SDO). However, several inevitable factors make this automatic identification challenging. While discrepancies between detection schemes have been noted in the literature, a comprehensive assessment of these discrepancies, which is still lacking, is of equal importance. Here we present the first community dataset for comparing automated coronal hole detection schemes. This dataset consists of 29 SDO images, all of which were selected by experienced observers to challenge automated schemes. We then use this dataset as input to 14 widely-applied automated schemes to study coronal holes and collect their detection results. From this, we select and study three SDO images that exemplify the most important lessons learned from this effort. We find that different detection schemes highlight significantly different physical properties of coronal holes. Motivated by these outcomes, we look into the effect of these results on the inferred magnetic connectivity in the corona by comparing the detected coronal hole boundaries to magnetic model solutions. These results, along with the database, will provide rich inputs to our understanding of coronal holes and their connection to the solar wind.

How to cite: Majumdar, S., Reiss, M., Muglach, K., Mason, E., Davies, E., and Chakraborty, S. and the S2-01 ISWAT Team: A Community Dataset for Comparing Automated Coronal Hole Detection Schemes and its Imprint on Magnetic Models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10009, https://doi.org/10.5194/egusphere-egu24-10009, 2024.

Coronal mass ejections (CMEs) are the strongest drivers of space weather. Measurements of the plasma parameters of CMEs, particularly magnetic fields entrained in the CME plasma, are crucial to understand their propagation, evolution, and geo-effectiveness. Spectral modeling of gyrosynchrotron (GS) emission from CME plasma has long been regarded as one of the most promising remote observation techniques for estimating spatially resolved CME plasma parameters. However, imaging the very low flux density CME GS emission in close proximity to the Sun with orders of magnitude higher flux density, has proven to be rather challenging. This challenge has only recently been met using the combination of data from the Murchison Widefield Array (MWA) and the recently developed spectropolarimetric snapshot imaging pipeline optimized for this data (P-AIRCARS). This has now brought routine detection of GS within reach, and the next challenge to be overcome is that of constraining the large number of free parameters in GS models. A few of these parameters are degenerate, and need to be constrained using the limited number of spectral measurements typically available. We present studies of spectropolarimetric modeling GS emissions from two different CMEs, which establish that these degeneracies can be broken using polarimetric imaging. 

However, this methodology is only useful to measure CME magnetic fields up to ~10 R๏. At  higher coronal heights and inner heliosphere CME magnetic fields can be estimated by measuring Faraday rotation of linearly polarized galactic/extragalactic radio sources. This method has been used using small field of view (FoV) instruments at high frequency (e.g., VLA) to measure magnetic fields along a single line of sight (LoS). We have recently started exploring the FR measurements due to CME using the MWA. The  advantage of using the MWA is its wide FoV and lower observing frequency. Lower observing frequency provides sensitivity to smaller magnetic fields. At the same time, wide FoV will provide simultaneous measurements along multiple LoSs and enable estimation of vector magnetic fields by constraining empirical flux-rope models of CMEs.  We present the challenges which need to be overcome to achieve these goals and some initial results.  

How to cite: Kansabanik, D., Oberoi, D., Vourlidas, A., and Mondal, S.: Measuring Magnetic Fields of Coronal Mass Ejection in Corona and Inner Heliosphere using Wide Field of View Spectro-polarimetric Radio Imaging, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4450, https://doi.org/10.5194/egusphere-egu24-4450, 2024.

For decades, the focus of polarimetric solar radio studies has been solely on circular polarization. This stemmed from the fact that the strong differential Faraday rotation in coronal plasma should completely obliterate any linear polarization component even if it were to be present (e.g., Grognard & McLean, 1973). Consequently, after a few reports in the late 50s and early 60s of successful detection of linearly polarized radio emissions from the Sun, the  consensus has essentially been to dismiss any detected linear polarization in the observed dynamic spectra as instrumental artifacts (e.g., Grognard & McLean, 1972; Boischot & Lecacheux, 1975). This assumption has been routinely used in calibrating solar polarimetric observations, even for recent studies (Morosan et al. 2022). The state-of-the-art polarimetric calibration algorithm, P-AIRCARS (Kansabanik et al., 2022a, 2022b, 2023) does not rely on any such assumptions. It provides high-fidelity and high-dynamic-range spectropolarimetric snapshot solar radio images using a new-generation instrument, the Murchison Widefield Array (MWA). This enables us to explore a part of phase space which was hitherto unexplored.

Using P-AIRCARS and the MWA, we present the first robust imaging-based evidence for linearly polarized emission in metre-wavelength solar radio bursts. This finding is corroborated by simultaneous observations with the upgraded Giant Metrewave Radio Telescope at the same spectral band. Moreover, our estimated upper limit on the Rotation Measure (RM) of ~50 rad m-2 are orders of magnitude lower than the previous estimates based on coronal models (e.g., ~103 rad m-2 by Bhonsle & McNarry, 1964). This low RM implies that the linear polarized emission has traversed much lower electron column densities, suggesting that it originates at much higher coronal heights. Interestingly, detections of linear polarization in stellar radio bursts have also been reported recently (Callingham et al., 2021; Bastian et al., 2022). We conclude by exploring some physical scenarios which can potentially give rise to such linearly polarized emissions in the solar corona.

How to cite: Dey, S., Kansabanik, D., Mondal, S., and Oberoi, D.: First robust detection of linear polarization from solar radio bursts, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14421, https://doi.org/10.5194/egusphere-egu24-14421, 2024.

Type-II solar radio bursts are plasma emissions generated by magnetohydrodynamic shocks that are predominantly driven by coronal mass ejections (CMEs), the most potent drivers of space weather. These narrow-bandwidth (~few MHz) emissions show slow drift towards lower frequencies in the dynamic spectrum and appear at the fundamental and harmonic of the local plasma frequency. The evolution and geo-effectiveness of CMEs are governed by their magnetic fields and interaction with the coronal magnetized plasma. Therefore, understanding the CME-entrained magnetic fields and the ambient medium is important. Polarimetric properties of type-II bursts provide promising diagnostics for measuring and understanding the magnetic field strength, and topology at the CME-shocks. In the literature, their polarization properties have been reported to vary from being unpolarized to very strongly circularly polarized, and no linear polarization has ever been reported. The vast majority of these studies rely on dynamic spectra which can only provide spatially integrated information. Instruments like Murchison Widefield Array (MWA) and robust spectropolarimetric snapshot solar imaging pipeline, P-AIRCARS, (Kansabanik et al., 2022, 2023) have enabled high-fidelity and high-dynamic range solar radio imaging with good temporal, spectral and reasonable angular resolution. Benefiting from these, we have used the MWA to carry out detailed imaging polarimetric characterization of a type-II solar radio burst. We detect a weak circular polarization of ~ 4% during the type II. We also report the first imaging detection of low levels of linearly polarized type-II emission. This robust but surprising detection goes against the conventional wisdom that differential coronal Faraday rotation should wipe out any linear polarization signatures in coronal emissions. We characterize the polarimetric structures in both circular and linear polarizations, meticulously investigating their temporal and spectral evolutions. Our study marks the start of the use of polarimetric imaging observations to further the understanding of type-II radio bursts and coronal propagation.  

How to cite: Majee, P., Kansabanik, D., and Oberoi, D.: First detailed polarimetric study of a type-II solar radio burst with the Murchison Widefield Array, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15960, https://doi.org/10.5194/egusphere-egu24-15960, 2024.

The study of characteristics, size, and shape variations of corotating interaction region (CIR) with changes in heliocentric distance is of scientific interest. The unique orbit parameters of the Solar Orbiter spacecraft (SOLO) and its set of equipment provide an opportunity to address the posed question. In our study, an attempt has been made to identify CIR regions using only data from the SOLO instruments.

The methodology for identifying CIR is well-developed. It involves in-situ observations of solar wind parameters, such as those proposed in the works of Hajra and Sunny, and verifies the potential presence of high-speed streams (HSS) from coronal holes. Such verification can be performed using SDO/AIA extreme ultraviolet observation data. This methodology can be easily implemented considering the near-Earth satellite constellation. Often, the trajectory of the SOLO passes out of the visibility range of near-Earth solar observation facilities, and there is no opportunity to verify the presence of coronal holes on the solar disk, which could be sources of HSS. In such cases, it is necessary to rely solely on the data from the SOLO instruments.

During the analysis of RPW instrument data, it was observed that sometimes the instrument registers shock events not confirmed by SWA instrument data. However, these events demonstrate an intense increase in solar wind speed and other parameters. The hypothesis has been put forward that multiple activations of the RPW instrument's SBM1 algorithm within a day can be used as a marker for the spacecraft's presence in the CIR zone. To validate this hypothesis, a comparative analysis of RPW data at the time of SBM1 events is conducted, comparing it with data from the SWA-PAS instrument. Based on the examples considered, a conclusion is drawn regarding the ability to track the spacecraft's entry and exit moments from the CIR region and assess the changes in CIR parameters when the spacecraft is within it.

This work is supported by the “Long-term program of support of the Ukrainian research teams at the Polish Academy of Sciences carried out in collaboration with the U.S. National Academy of Sciences with the financial support of external partners”.

How to cite: Chechotkin, D., Yakovlev, O., and Bilokon, O.: Detection of a corotating interaction region in solar wind using RPW and SWA instruments of the Solar Orbiter mission., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3926, https://doi.org/10.5194/egusphere-egu24-3926, 2024.