Extreme-ultraviolet jets and Hα surges in solar microflares

We analyzed simultaneous EUV data from the Transition Region and Coronal Explorer and H alpha 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 Her surges that are correlated with these jets. A careful comparison, however, revealed that the H alpha surges are not cospatial with the EW jets. Instead, the EUV jets are identified with bright jetlike features in the H alpha line center. Our results support a picture in which H alpha 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 H alpha surges.