Observational Analysis of Magnetic Reconnection Sequence

We conduct comprehensive analysis of an X2.0 flare to derive quantities indicative of magnetic reconnection in solar corona by following temporally and spatially resolved flare ribbon evolution in the lower atmosphere. The analysis reveals a macroscopically distinctive two-stage reconnection (Moore et al. 2001) marked by a clear division in morphological evolution, reconnection rate, and energy release rate. During the first stage, the flare brightening starts at and primarily spreads along the polarity inverion line (PIL) with the maximum apparent speed comparable to the local Alfven speed. The second stage is dominated by ribbon expansion perpendicular to the PIL at a fraction of the local Alfven speed. We further develope a data analysis approach, namely reconnection sequence analysis, to determine the connectivity and reconnection flux during the flare between a dozen magnetic sources defined from partitioning the photospheric magnetogram. It is found that magnetic reconnection proceeds sequentially between magnetic cells, and the observationally measured reconnection flux in major cells compare favorably with computations by a topological model of magnetic reconnection. The 3D evolution of magnetic reconnection is discussed with respect to its implication on helicity transfer and energy release through reconnection. Subject headings: Sun: activity – Sun: flares – Sun: magnetic fields