Using the time-dependent magneto-frictional model to study the kinematic emergence of a twisted flux rope into a coronal magnetic field arcade

Distinguishing the coronal magnetic field and its evolution can unlock key information on solar energetic eruptions such as the Coronal Mass Ejections (CMEs). CMEs are formed as magnetic flux ropes, i.e. magnetic field lines twisted about each other. They are the main drivers of space weather effects on Earth. Understanding the structure of the internal magnetic field of the CME would help determine the severity of the resulting geomagnetic storm. Predicting the onset and the orientation of the flux rope axis is a major focus of current space weather research. For this purpose, a numerical study on the kinematic emergence of a twisted flux rope into a coronal magnetic field is performed using the Magneto-frictional method (MFM). The MFM is an exciting prospect as it is sufficiently accurate and computationally inexpensive. The initiation of the eruption is through ideal Magnetohydrodynamic (MHD) kink instability. In this case, the kink instability occurs when the windings of the field lines about the flux rope axis exceeds a critical value. This thesis presents the set-up of the Fan & Gibson flux rope with different configurations. This was in hopes of studying the slow energization of the coronal field arcade with the emergence of a current carrying flux rope. The results of the simulations presented here show that the several key factors such as the height at which the flux rope is stopped and its twist play a major role in the dynamics of the flux rope in making it kink unstable. One of the main motivations was to use the results to discuss the performance of the MFM in comparison to MHD and how capable it is in capturing ideal MHD phenomenon. The simulations are also used to investigate the formation of sigmoidal current layer often seen before the onset of eruption. In the results presented here, the sigmoidal ’S’ shaped current layer is formed as the flux rope becomes kink unstable. This sigmoidal current layer is analysed for different configurations of the flux rope. These results have suggested that accurate dynamic modelling of the coronal magnetic field is essential for successful space weather prediction purposes

Coronal Conditions for the Occurrence of Type II Radio Bursts

Type II radio bursts are generally observed in association with flare-generated or coronal-mass-ejection-driven shock waves. The exact shock and coronal conditions necessary for the production of type II radio emission are still under debate. Shock waves are important for the acceleration of electrons necessary for the generation of the radio emission. Additionally, the shock geometry and closed field line topology, e.g., quasi-perpendicular shock regions or shocks interacting with streamers, play an important role for the production of the emission. In this study we perform a 3D reconstruction and modeling of a shock wave observed during the 2014 November 5 solar event. We determine the spatial and temporal evolution of the shock properties and examine the conditions responsible for the generation and evolution of type II radio emission. Our results suggest that the formation and evolution of a strong, supercritical, quasi-perpendicular shock wave interacting with a coronal streamer were responsible for producing type II radio emission. We find that the shock wave is subcritical before and supercritical after the start of the type II emission. The shock geometry is mostly quasi-perpendicular throughout the event. Our analysis shows that the radio emission is produced in regions where the supercritical shock develops with an oblique to quasi-perpendicular geometry

Assessing the Performance of EUHFORIA Modeling the Background Solar Wind

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. We present the 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 Advanced Composition Explorer (ACE) in-situ measurements. For the purposes 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 high-activity time interval considered. The quality of the modeled solar-wind parameters is found to be rather variable. Therefore, to better understand the results obtained we also qualitatively inspected characteristics of coronal holes, i.e. the 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 improvement of the model.Peer reviewe

Relativistic electron beams accelerated by an interplanetary shock

Collisionless shock waves have long been considered amongst the most prolific particle accelerators in the universe. Shocks alter the plasma they propagate through and often exhibit complex evolution across multiple scales. Interplanetary (IP) traveling shocks have been recorded in-situ for over half a century and act as a natural laboratory for experimentally verifying various aspects of large-scale collisionless shocks. A fundamentally interesting problem in both helio and astrophysics is the acceleration of electrons to relativistic energies (more than 300 keV) by traveling shocks. This letter presents first observations of field-aligned beams of relativistic electrons upstream of an IP shock observed thanks to the instrumental capabilities of Solar Orbiter. This study aims to present the characteristics of the electron beams close to the source and contribute towards understanding their acceleration mechanism. On 25 July 2022, Solar Orbiter encountered an IP shock at 0.98 AU. The shock was associated with an energetic storm particle event which also featured upstream field-aligned relativistic electron beams observed 14 minutes prior to the actual shock crossing. The distance of the beam's origin was investigated using a velocity dispersion analysis (VDA). Peak-intensity energy spectra were anaylzed and compared with those obtained from a semi-analytical fast-Fermi acceleration model. By leveraging Solar Orbiter's high-time resolution Energetic Particle Detector (EPD), we have successfully showcased an IP shock's ability to accelerate relativistic electron beams. Our proposed acceleration mechanism offers an explanation for the observed electron beam and its characteristics, while we also explore the potential contributions of more complex mechanisms.Comment: Main text: 6 pages, 2 figures. Supplementary material: 6 pages, 7 figure

Coronal Hole Detection and Open Magnetic Flux

Many scientists use coronal hole (CH) detections to infer open magnetic flux. Detection techniques differ in the areas that they assign as open, and may obtain different values for the open magnetic flux. We characterize the uncertainties of these methods, by applying six different detection methods to deduce the area and open flux of a near-disk center CH observed on 2010 September 19, and applying a single method to five different EUV filtergrams for this CH. Open flux was calculated using five different magnetic maps. The standard deviation (interpreted as the uncertainty) in the open flux estimate for this CH approximate to 26%. However, including the variability of different magnetic data sources, this uncertainty almost doubles to 45%. We use two of the methods to characterize the area and open flux for all CHs in this time period. We find that the open flux is greatly underestimated compared to values inferred from in situ measurements (by 2.2-4 times). We also test our detection techniques on simulated emission images from a thermodynamic MHD model of the solar corona. We find that the methods overestimate the area and open flux in the simulated CH, but the average error in the flux is only about 7%. The full-Sun detections on the simulated corona underestimate the model open flux, but by factors well below what is needed to account for the missing flux in the observations. Under-detection of open flux in coronal holes likely contributes to the recognized deficit in solar open flux, but is unlikely to resolve it.Peer reviewe

Generation of fine structures in interplanetary type III radio bursts induced by density inhomogeneities in the ambient plasma

International audienceSolar radio bursts have been studied for over 60 years, however some aspects of their generation and propagation remain to be open questions to the present day. It is generally accepted that majority of solar radio bursts observed in the corona is via the coherent plasma emission mechanism, and a substantial amount of work has been done to support this idea. Fine structures in solar radio bursts can therefore provide important input for understanding the background plasma characteristics. The presently available advanced ground-based radio imaging spectroscopic techniques (using e.g. LOFAR, MWA, etc.,) and space-based observations (Wind, STEREO A & B, Parker solar probe, Solar Orbiter) provide a unique opportunity to identify, and study fine structures observed in the low corona and interplanetary space.In this study, we focus on the radio fine structures observed in range of the hecto-kilometric wavelengths that were much less studied than the one in the metric-decametric range. We present for the first time three different types of fine structures observed in interplanetary type III radio bursts (radio signatures of fast electron beams propagating via open and quasi-open magnetic field lines). The presented fine structures show spectral characteristics similar to the striae-like fine structures observed within the type IIIb radio bursts at decametric wavelengths. We employ the probabilistic model for beam-plasma interaction to investigate the role of density inhomogeneities on the generation of the striae elements. The results suggest that there is a good correlation between the width of the striae elements and the scale of density inhomogeneities found in interplanetary space

Fundamental–Harmonic Pairs of Interplanetary Type III Radio Bursts

Type III radio bursts are not only the most intense but also the most frequently observed solar radio bursts. However, a number of their defining features remain poorly understood. Observational limitations, such as a lack of sufficient spectral and temporal resolution, have hindered a full comprehension of the emission process, especially in the hectokilometric wavelengths. Of particular difficulty is the ability to detect the harmonics of type III radio bursts. Here we report the first detailed observations of type III fundamental–harmonic pairs in the hectokilometric wavelengths, observed by the Parker Solar Probe. We present a statistical analysis of the spectral characteristics and polarization measurements of the fundamental–harmonic pairs. Additionally, we quantify various characteristics of the fundamental–harmonic pairs, such as the time delay and time profile asymmetry. Our report concludes that fundamental–harmonic pairs constitute a majority of all type III radio bursts observed during close encounters when the probe is in close proximity to the source region and propagation effects are less pronounced

Coronal Conditions for the Occurrence of Type II Radio Bursts

International audienceType II radio bursts are generally observed in association with flare-generated or coronal-mass-ejection-driven shock waves. The exact shock and coronal conditions necessary for the production of type II radio emission are still under debate. Shock waves are important for the acceleration of electrons necessary for the generation of the radio emission. Additionally, the shock geometry and closed field line topology, e.g., quasi-perpendicular shock regions or shocks interacting with streamers, play an important role for the production of the emission. In this study we perform a 3D reconstruction and modeling of a shock wave observed during the 2014 November 5 solar event. We determine the spatial and temporal evolution of the shock properties and examine the conditions responsible for the generation and evolution of type II radio emission. Our results suggest that the formation and evolution of a strong, supercritical, quasi-perpendicular shock wave interacting with a coronal streamer were responsible for producing type II radio emission. We find that the shock wave is subcritical before and supercritical after the start of the type II emission. The shock geometry is mostly quasi-perpendicular throughout the event. Our analysis shows that the radio emission is produced in regions where the supercritical shock develops with an oblique to quasi-perpendicular geometry

The Effect of the Parametric Decay Instability on the Morphology of Coronal Type III Radio Bursts

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

A Preliminary Statistical Analysis of Type-III Solar Burst Detections in Mars Reconnaissance Orbiter (MRO) Shallow Radar (SHARAD) Data

We present the results of a preliminary statistical analysis and classification of solar radio burst candidates detected by the Mars Reconnaissance Orbiter (MRO) Shallow Radar (SHARAD). We first analyze the histograms of the MRO SHARAD burst candidates as a function of MRO-STEREO true anomaly difference and received peak power. We then show the results of performing logistic regression to classify the MRO SHARAD burst candidates. Our results highlight the need for additional burst data to further refine the classifier, additional parameters to determine if bursts are present, and potentially explore a different classification technique to assign burst candidates with improved accuracy. Analyzing SRBs detected by MRO/SHARAD (as a potential additional solar radio-observatory) would enhance our understanding of solar radio burst propagation physics and behavior. We conclude by discussing the potential application, and challenges, of using these bursts as a source for subsurface radio sounding for future terrestrial and Mars missions