UK-Japan Cooperative Study of Solar Flares with the Yohkoh Mission

太阳观测卫星YOHKOH已成功运行了5年，从上一次活动高峰到整个下降阶段。所有的科学仪器都处于良好的状态，软x射线仪器甚至可以在最小的时候观察安静的太阳。通过对全部数据的研究，“磁重联”这一关键词被认为是日冕中产生高温等离子体的基本过程。Yohkoh新发现的环顶硬x射线源与“磁重联场景”一致。系统地研究了类氦硫谱线非热谱线加宽的特点。在谱线展宽最大值时，热等离子体的位置要么是足点，要么是耀斑环的环顶。对x射线喷流的统计研究也已完成，它们大多出现在混合磁极的活动区域，并且与新兴通量区密切相关。新出现的磁场与先前存在的日冕场的相互作用导致x射线喷流。与微耀斑的对应也表明这两种现象来自同一机制。另一方面，也出现了一些证据，表明基本日冕加热的机制不是“磁重联”。Yohkoh数据集收集了近一半的太阳周期，未来将利用这些数据进行太阳周期和太阳发电机机制的研究。1995年12月发射的SoHO卫星现在将停靠在拉格朗日点并开始观测。在太阳活动上升阶段的首次空间观测中，将高度鼓励与SoHO的联合观测和合作研究。

The sun observing satellite YOHKOH has been successfully operated for five years from the previous activity maximum and throughout the declining phase.All the scientific instruments onboard has been in good condition and the soft X-ray instruments can observe the quiet sun even at its minimum.Investigating the whole set of data, the keyword of "magnetic reconnection" has been emerged as a fundamental process for producing high temperature plasmas in the corona.Loop-top hard X-ray sources newly found by Yohkoh show consistency with the "magnetic reconnection scenario." Characteristic of nonthermal line broadenings seen in helium-like sulphur lines were systematically investigated.The locations of hot plasmas at the time of the line broadening maximum were either footpoints or loop top of flaring loops.Statistical studies of X-ray jets were also completed and they were mostly found in active regions with mixed magnetic polarity and strongly associated with emerging-flux regions.The interaction of emerged magnetic fields with pre-existing coronal field causes X-ray jets.Correspondence with micro-flares also suggests that the both phenomena come from the same mechanism.On the other hand, some evidence also appeared for the mechanism of basic coronal heating was something other than "magnetic reconnection."The Yohkoh dataset was compiled for nearly half of the solar cycle, with which studies of solar cycle and solar dynamo mechanisms will be done in future.The SoHO satellite launched in December 1995 will now station at the Lagrangean point and start its observations.Joint observations and collaborative studies with SoHO will be highly encouraged for the first space observations in the rising phase of the solar activity.