Multiwavelength Observations of Small-Scale Reconnection Events triggered by Magnetic Flux Emergence in the Solar Atmosphere

摘要

The interaction between emerging magnetic flux and the pre-existing ambientfield has become a "hot" topic for both numerical simulations andhigh-resolution observations of the solar atmosphere. The appearance ofbrightenings and surges during episodes of flux emergence is believed to be asignature of magnetic reconnection processes. We present an analysis of asmall-scale flux emergence event in NOAA 10971, observed simultaneously withthe Swedish 1-m Solar Telescope on La Palma and the \emph{Hinode} satelliteduring a joint campaign in September 2007. Extremely high-resolution G-band,H$\alpha$, and \ion{Ca}{2} H filtergrams, \ion{Fe}{1} and \ion{Na}{1}magnetograms, EUV raster scans, and X-ray images show that the emerging regionwas associated with chromospheric, transition region and coronal brightenings,as well as with chromospheric surges. We suggest that these features werecaused by magnetic reconnection at low altitude in the atmosphere. To supportthis idea, we perform potential and linear force-free field extrapolationsusing the FROMAGE service. The extrapolations show that the emergence site iscospatial with a 3D null point, from which a spine originates. This magneticconfiguration and the overall orientation of the field lines above the emergingflux region are compatible with the structures observed in the differentatmospheric layers, and remain stable against variations of the force-freefield parameter. Our analysis supports the predictions of recent 3D numericalsimulations that energetic phenomena may result from the interaction betweenemerging flux and the pre-existing chromospheric and coronal field.