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Preflare Phenomena in Eruptive Flares

We report the results of a statistical study of the relationship between eruptive solar flares and an observed Hα preflare phenomenon we call moving blueshift events (MBSEs). The Hα data were gathered using the Mees Solar Observatory CCD imaging spectrograph (MCCD). The 16 events in our data set were observed by both the MCCD and the Yohkoh Soft X-Ray Telescope, typically for at least 3 hr prior to the flare and in some cases repeatedly for several days prior to the flare. The data set contains both eruptive and noneruptive flares, without bias. Focusing on 3 hr periods before and after the flares, we found that the average rate of MBSEs prior to the flares was ~5 times greater prior to the 11 eruptive flares than prior to the five noneruptive ones. Also, the average rate of MBSEs dropped by a factor of ~6 after the eruptive flares. Earlier studies inferred that MBSEs reflect motions that originate in the readjustment of magnetic fields after magnetic reconnection. From the high correlation between eruptive flares and preflare MBSEs in the several hours prior to such events, we conclude that reconnection in the chromosphere or low corona plays an important role in establishing the conditions that lead to solar flare eruptions.