Extreme-Ultraviolet Jets and Hα Surges in Solar Microflares

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Abstract
We analyzed simultaneous EUV data from the Transition Region and Coronal Explorer and Hα data from Big Bear Solar Observatory. In the active region studied, we found several EUV jets that repeatedly occurred where pre-existing magnetic flux was "canceled" by newly emerging flux of opposite polarity. The jets look like Yohkoh soft X-ray jets, but are smaller and shorter lived than X-ray jets. They have a typical size of 4000-10,000 km, a transverse velocity of 50-100 km s-1, and a lifetime of 2-4 minutes. Each of the jets was ejected from a looplike bright EUV emission patch at the moment that the patch reached its peak emission. We also found dark Hα surges that are correlated with these jets. A careful comparison, however, revealed that the Hα surges are not cospatial with the EUV jets. Instead, the EUV jets are identified with bright jetlike features in the Hα line center. Our results support a picture in which Hα surges and EUV jets represent different kinds of plasma ejection—cool and hot plasma ejections along different field lines—which must be dynamically connected to each other. We emphasize the importance of observed flux cancellation and a small erupting filament in understanding the acceleration mechanisms of EUV jets and Hα surges.