报告题目：Magnetic Field and Energy Evolution in a Major Active Region Observed by SDO/HMI
报 告 人：Dr. Xundong Sun (孙旭东）， 斯坦福大学
摘 要：Full-disk, high-cadence observations from the the Helioseismic and Magnetic Imager (HMI) aboard the Solar Dynamic Observatory (SDO) now allow us to study the evolving magnetic field in solar active regions with great detail. Using a vector magnetogram series from SDO/HMI and a non-linear force-free extrapolation, we monitor the field and energy evolution in NOAA AR 11158, where the first X-class flare of Solar Cycle 24 took place. Several findings are as follows. 1) Fast flux emergence and shearing created a quadrupolar system. A substantial amount of electric current and free energy were concentrated near a low-lying sigmoidal filament channel. The inferred magnetic energy showed a sudden decrease during the X-class flare, which was enough to power the explosion. 2) The horizontal magnetic field in the AR core underwent fast, irreversible increase during the flare. As a result, the coronal field displayed a downward collapse motion, consistent with the "coronal implosion" conjecture. 3) A small bipole that emerged on the northeastern side of AR led to a series of "homologous eruptions"; all ejecta followed a highly inclined trajectory. The phenomenon can be explained by the asymmetric structure with anisotropic magnetic pressure. A persisting coronal null point was found in the model and the observation, which provides further evidence for our interpretation.
报告时间与地点：9月25日，上午9：30， 517 会议室
联 系 人：封莉
联系电话：83332177
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