Study of Ribbon Separation of a Flare Associated with a Quiescent Filament Eruption

Abstract

In this paper, we present a detailed study of a two-ribbon flare in the plage region observed by Kanzelhohe Solar Observatory (KSO), which is one of the stations in our global Hα network. We select this event due to its very clear filament eruption, two-ribbon separation, and association with a fast coronal mass ejection (CME). We study the separation between the two ribbons seen in Hα as a function of time and find that the separation motion consisted of a fast stage of rapid motion at a speed of about 15 km s-1 in the first 20 minutes and a slow stage with a separation speed of about 1 km s-1 lasting for 2 hr. We then estimate the rate of the magnetic reconnection in the corona, as represented by the electric fields Ec in the reconnecting current sheet, by measuring the ribbon motion speed and the magnetic fields obtained from MDI. We find that there were two stages as well in evolution of the electric fields: Ec = 1 V cm-1 averaged over 20 minutes in the early stage, followed by Ec = 0.1 V cm-1 in the subsequent 2 hr. The two stages of the ribbon motion and electric fields coincide with the impulsive and decaying phases of the flare, respectively, yielding clear evidence that the impulsive flare energy release is governed by the fast magnetic reconnection in the corona. We also measure the projected heights of the erupting filament from KSO Hα and SOHO/EIT images. The filament started to rise 20 minutes before the flare. After the flare onset, it was accelerated quickly at a rate of 300 m s-2, and in 20 minutes, reached a speed of at least 540 km s-1, when it disappeared beyond the limb in the EIT observations. The acceleration rate of the CME is estimated to be 58 m s-2 during the decay phase of the flare. The comparison of the height and velocity profiles between the filament and CME suggests that fast acceleration of mass ejections occurred during the impulsive phase of the flare, when the magnetic reconnection rate was also large, with Ec = 1 V cm-1.