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

Yohkoh在超过五年半的时间里一直运行良好，没有出现严重退化，其运行进入了一个阶段，我们可以在这个阶段进行系统的活动周期相关分析。与SoHO卫星的合作发挥了重要作用。SoHO于1995年12月成功推出。完成了半太阳周期数据库和分析软件的编制。在MSSL建立的Yohkoh数据分析中心（YDAC）在组织欧洲积极的国际合作方面发挥了关键作用，成为Yohkoh数据流的欧洲中心。有助于分析Yohkoh和SoHO数据的原子数据汇编也取得了良好进展，激发了英国和日本科学家之间的讨论。(1)不带准直器的BCS可以诊断1996年7月出现在太阳盘上的单个活动区域的SXV发射线，并与SERTS火箭实验合作，使1996年5月一个活动区域的温度结构得以揭示。(2)SoHO EIT/CDS和Yohkoh SXT同时观测到极区周围的喷流（微小喷流状结构），发现这些现象也是由磁重联触发的。(3)对HXT观测到的大量脉冲耀斑的分析，为非热粒子加速，特别是低能量截止点提供了新的解释。

Yohkoh has been working very well for more than five years and a half with no serious degradation and its operation entered into a phase in which we can do systematic activity-cycle related analyzes. Collaboration with the SoHO satellite had an important role. SoHO was successfully launched in December, 1995. Database of the half solar cycle and softwares for analysis were completed. Yohkoh Data Analysis Center (YDAC) set up in MSSL has playd a key role in organizing active international collaboration in Europe and became the European center of Yohkoh data flow. Compilation of atmic data helpful for analyzing the Yohkoh and SoHO data also made a good progress by activating discussions among UK and Japanese scientists.The followings are brief summary of the new results : (1)BCS without collimators could diagnose SXV emission lines from single active region on the solar disk that appeared in July, 1996, and collaboration with a rocket experiment, SERTS,made it possible to reveal the temperature structure of an active region in May 1996. (2)SoHO EIT/CDS and Yohkoh SXT simultaneously observed jetlets (tiny jet-like structure) around the polar region, and found that these phenomena were also triggered by magnetic reconnection. (3)Analysis of a large number of impulsive flares seen in HXT suggested a new interpretation for nonthermal particle acceleration, especially for low energy cutoffs.