A. V. Oreshina

Magnetic-topology evolution in NOAA AR 10501 on 2003 November 18

Context. NOAA AR 10501 produced three flares on 2003 November 18. Two of them were associated with coronal mass ejections (CMEs). Aims. We model the magnetic-field structure of the active region, study the magnetic-topology evolution, and propose a scenario of the observed events. Methods. The coronal magnetic field is reconstructed using a topological model (also called magnetic-charge model). We present an automatic method of choosing the magnetic charges for the case where the charges are located beneath the photosphere. The new method improves quantitative analysis of magnetograms and makes processing faster. Results. We demonstrate that coronal conditions became more favourable for magnetic reconnection before the flaring events. It is also shown that the magnetic-field configuration at the time of both CMEs was critical, close to what is called “topological trigger”. We assume that the topological trigger played a key role in the initiation of these CMEs.

On the heat conduction in a high-temperature plasma in solar flares

We have developed three types of mathematical models to describe the mechanisms of plasma heating in the corona by intense heat fluxes from a super-hot (Te ≳ 108 K) reconnecting current layer in connection with the problem of energy transport in solar flares. We show that the heat fluxes calculated within the framework of self-similar solutions using Fourier’s classical law exceed considerably the real energy fluxes known from present-day multi-wavelength observations of flares. This is because the conditions for the applicability of ordinary heat conduction due to Coulomb collisions of thermal plasma electrons are violated. Introducing anomalous heat conduction due to the interaction of thermal runaway electrons with ion-acoustic turbulence does not give a simple solution of the problem, because it produces unstable temperature profiles. Themodels incorporating the effect of collisional heat flux relaxation describe better the heat transport in flares than Fourier’s law and anomalous heat conduction.

A simple analytic model of reconnection in a high-temperature turbulent sheet

We present a simple model of high-temperature (T≥108 K) turbulent current sheets forming in magnetic-reconnection regions on the Sun. The model is based on an empirical formula by de Kluiver et al. (1991) for turbulent plasma conductivity and is apparently valid over a wide range of physical conditions. A comparison of the new results with known test calculations suggests agreement between the theoretical and empirical approaches to calculating the anomalous conductivity in turbulent plasma. The energy release in current sheets is powerful enough for flares, coronal transients, and coronal mass ejections to be interpreted.

Analytical description of charged particle motion in a reconnecting current sheet

We have obtained an analytical solution to the equation of motion in the guiding center approximation for nonrelativistic charged particles in a reconnecting current sheet with a three-component magnetic field. Given the electric field attributable to magnetic reconnection, the solution describes stable and unstable three-dimensional particle orbits. We have found the domain of input parameters at which the motion is stable. A physical interpretation of the processes affecting the stability of the motion is given. Charge separation is shown to take place in the sheet during the motion: oppositely charged particles are localized mostly in different regions of the current sheet. A formula is derived for the particle energy in stable and unstable orbits. The results obtained by numerical and analytical methods are compared.

Analytical and numerical investigations of relativistic particle acceleration in a current layer

We investigate the motion of a charged particle in the process of acceleration up to relativistic energies in a superhot turbulent current layer with three components of the magnetic field. We solve analytically the relativistic equation of motion that has been averaged over the particle gyration in the magnetic field. The obtained results are compared with numerical solution of the ordinary (without averaging) equation of motion. The analytical solution describes a stable motion, i.e. when a particle remains in the reconnecting current layer until it reaches its edges. The stability conditions are found imposed on the electric and magnetic fields in the layer. Particles with positive and negative charges have different behaviours. The numerical solution has confirmed the conclusions of the analytical approach. Applications to solar flares are discussed.