Plasmoid Dynamics in Flare Reconnection and the Frequency Drift of the Drifting Pulsating Structure

Abstract

In the paper by Kliem, Karlický, and Benz (Astron. Astrophys. 360, 715, 2000) it was suggested, that plasmoids formed during the bursty regime of solar flare reconnection can be "visualised" in the radio spectra as drifting pulsating structures via accelerated particles trapped inside the plasmoid. In the present paper we investigate this idea in detail. First, simple statistical analysis supporting this hypothesis is presented. Then, by using the 2.5-D MHD (including gravity) model solar flare reconnection in the inhomogeneous, stratified atmosphere is simulated and the formation and subsequent ejection of the plasmoid is demonstrated. The ejected plasmoid, which is considered to be a trap for accelerated electrons, is traced and its plasma parameters are computed. To estimate the associated plasma radio emission we need to know locations of accelerated electrons and corresponding plasma frequencies. General considerations predict that these electrons should be distributed mainly along the magnetic separatrix surfaces and this was confirmed by using a particle-in-cell simulation. Finally, under some simplifying assumptions the model dynamic radio spectrum is constructed. The relation between the global frequency drift and the plasmoid motion in the inhomogeneous ambient atmosphere is studied. The results are discussed with respect to the observed drifting pulsation structures and their possible utilisation for flare magnetic field diagnostics.

Review on Current Sheets in CME Development: Theories and Observations

“…The second feature noticed by Forbes and Priest (1983) has continuously been displayed and duplicated in recent numerical experiments with higher and higher resolutions (Riley et al 2007;Bárta et al 2008Bárta et al , 2010Bárta et al , 2011aBárta et al , 2011bShen et al 2011Shen et al , 2013. These experiments also confirmed that it is inevitable for magnetic islands to form in the CS developed in the coronal environment of high S, and that small islands have a tendency to merge into bigger islands.…”

“…From an alternative point of view, Bárta et al (2008) performed a simple statistical analysis for the existing observational results, and found the hypothesis of Kliem et al (2000) that internal features could be visualized in the radio spectra supported by observations. By using a 2.5-D MHD model, they simulated reconnection in a Kopp-Pneuman configuration with an inhomogeneous and gravitationally stratified atmosphere, and demonstrated the formation and subsequent ejection of plasmoids inside the CS.…”

“…On the basis of their previous works (Bárta et al 2008), Bárta et al (2011b) enhanced the resolution of grids in their experiments, and studied in detail how the magnetic field could be quickly dissipated in the reconnection process. Their results support the theory of Shibata and Tanuma (2001), indicating that the energy associated with large scale structures was successively transferred to that associated with small structures until the kinetic process dominates the energy conversion.…”

Radio spectra generated during coalescence processes of plasmoids in a flare current sheet

“…Nevertheless, there are also the cases when the plasmoids move downwards and the associated DPSs drift to higher frequencies. The plasma density inside the plasmoid differs from that in the surrounding solar atmosphere, therefore this difference needs to be considered in the height estimation of the DPS source in the solar atmosphere from its DPS spectrum (for more details, see Bárta et al 2008a). An example of the DPS observed at the beginning of the May 21, 2002 flare is shown in Fig.…”

“…The DPSs are usually observed in the frequency range 0.6−2 GHz, which corresponds to the plasma densities in the radio sources n e = 4.4 × 10 9 −4.9 × 10 10 cm −3 . The global drift of DPSs is typically in the range −20−20 MHz s −1 (Bárta et al 2008a).…”