报告题目：MHD simulations of flux emergence in an open field region: Jet formation and explosive events

报告人：Dr. Klaus Galsgaard(丹麦，哥本哈根大学)

报告时间：2015年7月1日(星期三)下午3点

报告地点：闻天楼南楼208

报告摘要：The launch of Hinode in 2006 was the start of a new interest in the jet phenomena in open field regions. Observations by the Hinode, SDO and Stereo satellites have shown that one characteristic jet type dominates, namely the so-called Eiffel-tower or inverted-Y jet. The name arise from the jet's appearance in X-ray, where they are seen to have two small "legs" below a long monolith structure representing the jet. This structure is interpreted as the result of the interaction between a bipolar field and and the unipolar magnetic background field. This picture naturally leads to magnetic reconnection between the two flux regions, where two the high velocity outflows from the diffusion region forms both the long jet structure and the underlying hot loop system. To investigate this scenario in detail, we have performed MHD experiments of the emergence of a magnetic dipole region into an uniform open field region. We find the initial jet phase to last on the order of 10 minutes, showing a smoothly evolving structure which, for a part of the evolution, closely resemblance the inverted-y structure. A number of characteristic structures arises around the foot-point region of the loop that may be compared with observations. Towards the end of this "steady state" inverted-y jet phase, the amount of flux in the emerged bipolar region is being exhausted by the reconnection process and the dynamical evolution enters a new phase. In this phase five eruptions take place in different parts of the remaining magnetic structure. These eruptions arises from only three main areas of the emerged flux region, implying that the same physical region can host repeated instabilities in the magnetic field. In the talk we discuss the general evolution of the jet, and show examples of the eruptive behaviour, while also trying to explain the reason for these different eruptions.