题　  目：Magnetic helicity in emerging active regions computed from the HMI data

报 告 人：Liu Yang  斯坦福大学

报告摘要：Magnetic helicity in solar active regions is a volume integrated ideal MHD invariant that describes how energetic and complex an active region is. Computation of this quantity is challenging: estimating helicity not only requires info-rmation of magnetic field but also vector potential in the volume. Alternatively, one can integrate over time the helicity-flux across solar surface to estimate helicity stored in an active region. Accurate estimate of the coronal helicity requires that the computation be done from very beginning  of　 emergence of the active region. Full disk field-of-view, continuous observation coverage, high temporal and spatial resolutions, and consistent data quality, these specifications of observational data taken by the HMI allow one to study  magnetic helicity-injection into active-region corona, especially their buildup and evolution during flux emergence because full disk measurement provides  data  that catch very beginning of emergence of active regions.

In this talk, I discuss the methods that have been used to calculate the helicity flux across the photosphere, present a statistical study  of magnetic  helicity in solar active regions based on a sample of 56 emerging active regions observed by HMI during the rising phase of cycle 24, and comment the hypothesis made by Demoulin and Berger (2003) that allows one  to calculate  magnetic  helicity flux using the time-series line-of-sight magnetic field data only.

报告时间：2012年9月3日（星期一）上午10:30

报告地点：紫台大楼517会议室

联 系 人：黎辉 83332177

欢迎大家积极参加！

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