arXiv subjects

Marian Karlicky

Publications and source records attributed to Marian Karlicky.

24 records · Page 2Linked to original sources

arXiv2013

Fragmentation of electric currents in the solar corona by plasma flows

We consider a magnetic configuration consisting of an arcade structure and a detached plasmoid, resulting from a magnetic reconnection process, as is typically found in connection with solar flares. We study spontaneous current fragmentation caused by shear and vortex plasma flows. An exact analytical transformation method was applied to calculate self-consistent solutions of the nonlinear stationary MHD equations. The assumption of incompressible field-aligned flows implies that both the Alfven Mach number and the mass density are constant on field lines. We first calculated nonlinear MHS equilibria with the help of the Liouville method, emulating the scenario of a solar eruptive flare configuration with plasmoids and flare arcade. Then a Mach number profile was constructed that describes the upflow along the open magnetic field lines and implements a vortex flow inside the plasmoid. This Mach number profile was used to map the MHS equilibrium to the stationary one. We find that current fragmentation takes place at different locations within our configuration. Steep gradients of the Alfven Mach number are required, implying the strong influence of shear flows on current amplification and filamentation of the MHS current sheets. Crescent- or ring-like structures appear along the outer separatrix, butterfly structures between the upper and lower plasmoids, and strong current peaks close the lower boundary. Impressing an intrinsic small-scale structure on the upper plasmoid results in strong fragmentation of the plasmoid. Hence fragmentation of current sheets and plasmoids is an inherent property of MHD theory. Transformations from MHS into MHD steady-states deliver fine-structures needed for plasma heating and acceleration of particles and bulk plasma flows in dissipative events that are typically connected to magnetic reconnection processes in flares and coronal mass ejections.

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arXiv2009

Stationary stagnation point flows in the vicinity of a 2D magnetic null point: I. Systems with vanishing electric field and an X-type magnetic null point

The appearance of eruptive space plasma processes, e.g., in eruptive flares as observed in the solar atmosphere, is usually assumed to be caused by magnetic reconnection. The process of magnetic reconnection is often connected with singular points of the magnetic field. We therefore analyse the system of stationary resistive/non-ideal magnetohydrodynamics (MHD) in the vicinity of singular points of flow and field to determine the boundary between reconnection solutions and non-reconnective solutions. We find conditions to enable the plasma to cross the magnetic separatrices also inside the current sheet, close to the current maximum. The results provide us with the topological and geometrical skeleton of the resistive MHD fields. We therefore have to perform a local analysis of almost all non-ideal MHD solutions with a generalized non-idealness. We use Taylor expansions of the magnetic field, the velocity field and all other physical quantities, including the non-idealness, and with the method of a comparison of the coefficients, the non-linear resistive MHD system is solved analytically. It turns out that not every non-ideal flow is a reconnective flow and that pure resistive/non-ideal MHD only allows for reconnection-like solutions, even if the non-idealness is localized to the region around the magnetic null point. It is necessary that the flow close to the magnetic X-point is also of X-point type to guarantee positive dissipation of energy and annihilation of magnetic flux. If the non-idealness has only a one-dimensional, sheet-like structure, only one separatrix line can be crossed by the plasma flow, similar to reconnective annihilation solutions.

astro-ph.SR↗

arXiv2009

Successive Solar Flares and Coronal Mass Ejections on 2005 September 13 from Noaa Ar 10808

We present a multiwavelength study of the 2005 September 13 eruption from NOAA 10808 that produced total four flares and two fast coronal mass ejections (CMEs) within 1.5 hours. Our primary attention is paid to the fact that these eruptions occurred in close succession in time, and that all of them were located along an S-shaped magnetic polarity inversion line (PIL) of the active region. In our analysis, (1) the disturbance created by the first flare propagated southward along the PIL to cause a major filament eruption that led to the first CME and the associated second flare underneath. (2) The first CME partially removed the overlying magnetic fields over the northern Delta spot to allow the third flare and the second CME. (3) The ribbon separation during the fourth flare would indicate reclosing of the overlying field lines opened by the second CME. It is thus concluded that this series of flares and CMEs are interrelated to each other via magnetic reconnections between the expanding magnetic structure and the nearby magnetic fields. These results complement previous works made on this event with the suggested causal relationship among the successive eruptions.

astro-ph.SR↗

arXiv2007

Separation of accelerated electrons and positrons in the relativistic reconnection

We study an acceleration of electrons and positrons in the relativistic magnetic field reconnection using a 2.5-D particle-in-cell electromagnetic relativistic code. We consider the model with two current sheets and periodic boundary conditions. The electrons and positrons are very effectively accelerated during the tearing and coalescence processes of the reconnection. We found that near the X-points of the reconnection the positions of electrons and positrons differ. This separation process is in agreement with those studied in the previous papers analytically or by test particle simulations. We expect that in dependence on the magnetic field connectivity this local separation can lead to global spatial separation of the accelerated electrons and positrons. A similar simulation in the electron-proton plasma with the proton-electron mass ratio m_i/m_e = 16 is made.

astro-ph↗

arXiv2007

Hydrogen Balmer line formation in solar flares affected by return currents

Aims. We investigate the effect of the electric return currents in solar flares on the profiles of hydrogen Balmer lines. We consider the monoenergetic approximation for the primary beam and runaway model of the neutralizing return current. Methods. Propagation of the 10 keV electron beam from a coronal reconnection site is considered for the semiempirical chromosphere model F1. We estimate the local number density of return current using two approximations for beam energy fluxes between $4\times 10^{11}$ and $1\times 10^{12} {\rm erg cm^{-2} s^{-1}}$. Inelastic collisions of beam and return-current electrons with hydrogen are included according to their energy distributions, and the hydrogen Balmer line intensities are computed using an NLTE radiative transfer approach. Results. In comparison to traditional NLTE models of solar flares that neglect the return-current effects, we found a significant increase emission in the Balmer line cores due to nonthermal excitation by return current. Contrary to the model without return current, the line shapes are sensitive to a beam flux. It is the result of variation in the return-current energy that is close to the hydrogen excitation thresholds and the density of return-current electrons.

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arXiv2007

The Eruption from a Sigmoidal Solar Active Region on 2005 May 13

This paper presents a multiwavelength study of the M8.0 flare and its associated fast halo CME that originated from a bipolar active region NOAA 10759 on 2005 May 13. The source active region has a conspicuous sigmoid structure at TRACE 171 A channel as well as in the SXI soft X-ray images, and we mainly concern ourselves with the detailed process of the sigmoid eruption as evidenced by the multiwavelength data ranging from Halpha, WL, EUV/UV, radio, and hard X-rays (HXRs). The most important finding is that the flare brightening starts in the core of the active region earlier than that of the rising motion of the flux rope. This timing clearly addresses one of the main issues in the magnetic eruption onset of sigmoid, namely, whether the eruption is initiated by an internal tether-cutting to allow the flux rope to rise upward or a flux rope rises due to a loss of equilibrium to later induce tether cutting below it. Our high time cadence SXI and Halpha data shows that the first scenario is relevant to this eruption. As other major findings, we have the RHESSI HXR images showing a change of the HXR source from a confined footpoint structure to an elongated ribbon-like structure after the flare maximum, which we relate to the sigmoid-to-arcade evolution. Radio dynamic spectrum shows a type II precursor that occurred at the time of expansion of the sigmoid and a drifting pulsating structure in the flare rising phase in HXR. Finally type II and III bursts are seen at the time of maximum HXR emission, simultaneous with the maximum reconnection rate derived from the flare ribbon motion in UV. We interpret these various observed properties with the runaway tether-cutting model proposed by Moore et al. in 2001.

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