arXiv subjects

Georgios Chouliaras

Publications and source records attributed to Georgios Chouliaras.

4 recordsLinked to original sources

arXiv2026

Automatic detection of Flare Ribbon Fine Structures as Proxies for Plasmoid Dynamics in Flare Reconnection

Flare ribbons often display fine structures along their fronts that are commonly interpreted as signatures of intermittent reconnection dynamics including plasmoid formation in the flare current sheet. We introduce an automated method that detects and tracks the spiral- and wave-like imprints of these structures and as a proof of concept apply it to maps of magnetic field-line length from a high-resolution 3D eruptive-flare simulation. The workflow applies the correlation-dimension method, density-based clustering, and a minimum-area ellipse fit to summarise each feature. We show that across the simulated flare, the detected spirals remain locked to the ribbon's outward motion while drifting coherently along the ribbon. The two ribbons show opposite along-ribbon drift and motion away from their hooks in accordance with theoretical expectations, with instantaneous speeds of 10-800 km s^1, all well below the local surface Alfven speed. Occurrence, lifetimes, and mean magnetic flux of the features peak during the impulsive phase. The distribution of per-spiral mean unsigned flux shows a scale-free tail above roughly 6x10^18 Mx with a power-law exponent near 3.4. Together, these results show that bursty, plasmoid-mediated flare reconnection leaves a clear, measurable signature on the flare ribbons. The method provides a practical surface diagnostic of ribbon fine structure that can potentially be used to inform our understanding of three-dimensional magnetic reconnection in the flare current sheet.

astro-ph.SR↗

arXiv2024

Magnetic flux emergence and solar eruptions in partially ionized plasmas

We have performed 3D MHD simulations to study the effect of partial ionization in the process of magnetic flux emergence in the Sun. In fact, we continue previous work and we now focus: 1) on the emergence of the magnetic fields above the solar photosphere and 2) on the eruptive activity, which follows the emergence into the corona. We find that in the simulations with partial ionization (PI), the structure of the emerging field consists of arch-like fieldlines with very little twist since the axis of the initial rising field remains below the photosphere. The plasma inside the emerging volume is less dense and it is moving faster compared to the fully ionized (FI) simulation. In both cases, new flux ropes (FR) are formed due to reconnection between emerging fieldlines, and they eventually erupt in an ejective manner towards the outer solar atmosphere. We are witnessing three major eruptions in both simulations. At least for the first eruption, the formation of the eruptive FR occurs in the low atmosphere in the FI case and at coronal heights in the PI case. Also, in the first PI eruption, part of the eruptive FR carries neutrals in the high atmosphere, for a short period of time. Overall, the eruptions are relatively faster in the PI case, while a considerable amount of axial flux is found above the photosphere during the eruptions in both simulations.

astro-ph.SR↗

arXiv2023

Effects of partial ionization on magnetic flux emergence in the Sun

We have performed 3-D numerical simulations to investigate the effect of partial ionization on the process of magnetic flux emergence. In our study, we have modified the single-fluid MHD equations to include the presence of neutrals and have performed two basic experiments: one that assumes a fully ionized plasma (FI case) and one that assumes a partially ionized plasma (PI case). We find that the PI case brings less dense plasma to and above the solar surface. Furthermore, we find that partial ionization alters the emerging magnetic field structure, leading to a different shape of the polarities in the emerged bipolar regions compared to the FI case. The amount of emerging flux into the solar atmosphere is larger in the PI case, which has the same initial plasma beta as the FI case, but a larger initial magnetic field strength. The expansion of the field above the photosphere occurs relatively earlier in the PI case, and we confirm that the inclusion of partial ionization reduces cooling due to adiabatic expansion. However, it does not appear to work as a heating mechanism for the atmospheric plasma. The performance of these experiments in three dimensions shows that PI does not prevent the formation of unstable magnetic structures, which erupt into the outer solar atmosphere.

astro-ph.SR↗

arXiv2022

Application of an Upwind Integration Method to Plane Parallel Hall-MHD

We study the impact of an Upwind scheme on the numerical convergence of simulations of the Hall and Ohmic effect in neutron stars crusts. While simulations of these effects have explored a variety of geometries and wide ranges of physical parameters, they are limited to relatively low values of the Hall parameter, playing the role of the magnetic Reynolds number, which should be not exceed a few hundred for numerical convergence. We study the evolution of the magnetic field in a plane-parallel Cartesian geometry. We discretise the induction equation using a finite difference scheme and then integrate it via the Euler forward method. Two different approaches are used for the integration of the advective terms appearing in the equation: a Forward Time and Central in Space (FTCS) and an Upwind scheme. We compare them in terms of accuracy and performance. We explore the impact of the Upwind method on convergence according to the ratio of planar to vertical field and the Hall parameter. In the limit of a low strength planar field the use of an Upwind scheme provides a vast improvement leading to the convergence of simulations where the Hall parameter is 2 orders of magnitude higher than that of the FTCS. Upwind is still better if the planar field is stronger, yet, the difference of the maximum value of the Hall parameter reached is within a factor of 10 or a few. Moreover, we notice if the schemes diverge their behaviour is very different, with FTCS producing infinite energy, while the Upwind scheme only temporarily increasing the overall magnetic field energy. Overall, the Upwind scheme enhances the efficiency of the simulations allowing the exploration of environments with higher value of electric conductivity getting us closer than before to realistic environmental conditions of magnetars.

astro-ph.IM↗