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Solar flare termination shocks have been suggested as one of the promisingdrivers for particle acceleration in solar flares, yet observational evidenceremains rare. By utilizing radio dynamic spectroscopic imaging of decimetricstochastic spike bursts in an eruptive flare, Chen et al. found that the burstsform a dynamic surface-like feature located at the ending points of fast plasmadownflows above the looptop, interpreted as a flare termination shock. Onepiece of observational evidence that strongly supports the termination shockinterpretation is the occasional split of the emission band into two finerlanes in frequency, similar to the split-band feature seen infast-coronal-shock-driven type II radio bursts. Here we perform spatially,spectrally, and temporally resolved analysis of the split-band feature of theflare termination shock event. We find that the ensemble of the radio centroidsfrom the two split-band lanes each outlines a nearly co-spatial surface. Thehigh-frequency lane is located slightly below its low frequency counterpart by~0.8 Mm, which strongly supports the shock upstream-downstream interpretation.Under this scenario, the density compression ratio across the shock front canbe inferred from the frequency split, which implies a shock with a Mach numberof up to 2.0. Further, the spatiotemporal evolution of the density compressionalong the shock front agrees favorably with results from magnetohydrodynamicssimulations. We conclude that the detailed variations of the shock compressionratio may be due to the impact of dynamic plasma structures in the reconnectionoutflows, which results in distortion of the shock front.

Radio Spectroscopic Imaging of a Solar Flare Termination Shock: Split-Band Feature as Evidence for Shock Compression