arXiv subjects

Boris V. Somov

Publications and source records attributed to Boris V. Somov.

7 recordsLinked to original sources

arXiv2025

Topological ignition of the stealth coronal mass ejections

One of hot topics in the solar physics are the so-called 'stealth' coronal mass ejections (CME), which are not associated with any appreciable energy release events in the lower corona, such as the solar flares. It is often assumed recently that these phenomena might be produced by some specific physical mechanism, but no particular suggestions were put forward. It is the aim of the present paper to show that a promising explanation of the stealth CMEs can be based on the so-called 'topological' ignition of the magnetic reconnection, when the magnetic null point is produced by a specific superposition of the remote sources (sunspots) rather than by the local current systems. As follows from our numerical simulations, the topological model explains very well all basic features of the stealth CMEs: (i) the plasma eruption develops without an appreciable heat release from the spot of reconnection, i.e., without the solar flare; (ii) the spot of reconnection (magnetic null point) can be formed far away from the location of the magnetic field sources; (iii) the trajectories of eruption are usually strongly curved, which can explain observability of CMEs generated behind the solar limb.

astro-ph.SR↗

arXiv2023

The unipolar solar flares as a manifestation of the 'topological' magnetic reconnection

Solar flares - which are the most prominent manifestation of the solar activity - typically manifest themselves as a single or a set of luminous arcs (magnetic flux tubes) rooted in regions of opposite polarity in the photosphere. However, a careful analysis of the archival data by Hinode satellite sometimes reveals surprising cases of flaring arcs whose footpoints belong to regions of the same polarity or to areas without any appreciable magnetic field. Despite the counterintuitive nature of this phenomenon, it can be reasonably interpreted in the framework of the so-called 'topological model' of magnetic reconnection, where a magnetic null point is formed due to specific superposition of influences from remote sources rather than by local current systems. As a result, the energy release propagates along a separator of the flipping two-dome structure rather than along a fixed magnetic field line. Therefore, the luminous arc needs not to be associated anymore immediately with the magnetic sources. Here, we report both observational cases of the above-mentioned type as well as provide their theoretical model and numerical simulations.

astro-ph.SR↗

arXiv2022

Topological Quantification of the "Anemone" (Branching) Solar Flares

The so-called "anemone" solar flares are an interesting type of the space plasma phenomena, where multiple null points of the magnetic field are connected with each other and with the magnetic sources by the separators, thereby producing the complex branching configurations. Here, using the methods of dynamical systems and Morse-Smale theory, we derive a few universal topological relations between the numbers of the null points and sources of various kinds with arbitrary arrangement in the above-mentioned structures. Such relations can be a valuable tool both for a quantification of the already-observed anemone flares and for a prediction of the new ones in complex magnetic configurations.

astro-ph.SR↗

arXiv2020

New Types of the Chromospheric Anemone Microflares: Case Study

The chromospheric anemone microflares (AMF) are the transient solar phenomena whose emission regions have a multi-ribbon configuration. As distinct from the so-called "atypical" solar flares, also possessing a few ribbons, the temporal and spatial scales of AMFs are a few times less, and the configuration of their ribbons is more specific (star-like). The previously reported AMFs had typically three or, less frequently, four ribbons; and it was shown in our recent paper (Dumin and Somov: 2019, Astron. Astrophys. 623, L4) that they can be reasonably described by the so-called GKSS model of magnetic field, involving as few as four point-like magnetic sources with various polarity and arrangement. To seek for the new types of AMFs, we performed inspection of the large set of the emission patterns in the chromospheric line Ca II H recorded by Hinode/SOT and confronted them with the respective magnetograms obtained by SDO/HMI. As follows from this analysis, it is really possible to identify the new unusual AMFs. Firstly, these are the flares occurring in the regions with unbalanced magnetic flux. Secondly, and most interesting, it is possible to identify the AMFs with much more complex spatial configurations, e.g., involving five luminous ribbons with a nontrivial arrangement. As follows from the corresponding magnetograms, they are produced by the effective magnetic sources (sunspots) of different polarity with intermittent arrangement, but their number is greater than in the standard GKSS model.

astro-ph.SR↗

arXiv2017

Observation of "Topological" Microflares in the Solar Atmosphere

We report on observation of the unusual kind of solar microflares, presumably associated with the so-called "topological trigger" of magnetic reconnection, which was theoretically suggested long time ago by Gorbachev et al. (Sov. Ast. 1988, v.32, p.308) but has not been clearly identified so far by observations. As can be seen in pictures by Hinode SOT in CaII line, there may be a bright loop connecting two sunspots, which looks at the first sight just as a magnetic field line connecting the opposite poles. However, a closer inspection of SDO HMI magnetograms shows that the respective arc is anchored in the regions of the same polarity near the sunspot boundaries. Yet another peculiar feature is that the arc flashes almost instantly as a thin strip and then begins to expand and decay, while the typical chromospheric flares in CaII line are much wider and propagate progressively in space. A qualitative explanation of the unusual flare can be given by the above-mentioned model of topological trigger. Namely, there are such configurations of the magnetic sources on the surface of photosphere that their tiny displacements result in the formation and fast motion of a 3D null point along the arc located well above the plane of the sources. So, such a null point can quickly ignite a magnetic reconnection along the entire its trajectory. Pictorially, this can be presented as flipping the so-called two-dome magnetic-field structure (which is just the reason why such mechanism was called topological). The most important prerequisite for the development of topological instability in the two-dome structure is a cruciform arrangement of the magnetic sources in its base, and this condition is really satisfied in the case under consideration.

astro-ph.SR↗

arXiv2015

What is Generic Structure of the 3D Null-Point Magnetic Reconnection?

The probability of occurrence of various topological configurations of the 3D null-point reconnection in a random magnetic field is studied. It is found that the non-axisymmetrical six-tail configuration (or "improper radial null") should play the dominant role; while all other types of reconnection, in particular, the axially-symmetric fan-like structures (or "proper radial nulls") are realized with a much less probability. A characteristic feature of the six-tail configuration is that at the sufficiently large scales it is approximately reduced to the well-known 2D X-type structure; and this explains why the 2D models of reconnection usually work quite well.

physics.plasm-ph↗

arXiv2009

Magnetic reconnection and topological trigger in physics of large solar flares

Solar flares are accessible to a broad variety of observational methods to see and investigate the {\em magnetic reconnection} phenomenon in high-temperature strongly-magnetized plasma of the solar corona. An analysis of the topological peculiarities of magnetic field in active regions shows that the {\em topological trigger} effect is necessary to allow for in order to construct models for large eruptive flares. The topological trigger is not a resistive instability which leads to a change of the topology of the field configuration from pre- to post reconnection state. On the contrary, the topological trigger is a quick change of the global topology, which dictates the fast reconnection of collisional or collisionless nature. The current state of the art and development potential of the theory of collisionless reconnection in the strong magnetic fields related to large flares are briefly reviewed. Particle acceleration is considered in collapsing magnetic traps created by reconnection. In order to explain the formation of coronal X-ray sources, the Fermi acceleration and betatron mechanism are simultaneously taken into account analytically in a collisionless approximation. Finally, the emphasis is on urgent unsolved problems of solar flare physics.

astro-ph.SR↗