High-Resolution, High-Precision Observation of Solar X-Ray Images

所有的科学仪器都在轨道上工作得很好，在Yohkoh发射两周年之际，仍然向地面发送有价值的数据。他们正在观测处于活动衰退阶段的太阳。第一年获得的数据开始分发给世界太阳能界，并附有一个方便的数据分析软件包。鼓励世界范围合作的制度取得了进展。Yohkoh的重要发现之一是揭示了日冕活动的基本过程是由磁剪切触发的磁重联。在太阳耀斑中，有大量的证据表明，磁重联过程释放出磁能，热等离子体填充到色球蒸发的磁环中。观察到尖形或X形结构及其演化，这与重联假说一致。还发现了脉冲环顶硬X射线源，为太阳耀斑中的磁重联提供了进一步的证据。我们可以注意到，这些观测大大增加了在磁中性片中看到重联点的可能性。在耀斑初始阶段的软X射线谱中，观测到了热等离子体的完全蓝移发射线，这表明色球蒸发的热能传输机制是有效的。此外，整个日冕被发现非常动态，并且发现了许多X射线增亮和/或X射线喷流。它们也是磁重联产生的候选者。

All the scientific instruments are working well in orbit and still sending the valuable data to the ground at the second anniversary of the launch of Yohkoh. They are observing the sun in the declining phase of activity. The data obtained in the first year started to be distributed to the world solar community with a convenient software package for the data analysis. The system to encourage world-wide collaborations has made progress. One of the important discoveries of Yohkoh is that the magnetic reconnection triggered by magnetic shears is revealed to the fundamental process of the solar coronal activity. In solar flares ample evidences are found to prove the magnetic energy is released by the process of magnetic reconnection, and then hot plasmas fill into the magnetic loop evaporated from the chromosphere. Cusp-shaped or sometimes X-shaped structures and their evolutions are observed, which is found consistent with the reconnection hypothesis. Impulsive loop-top hard X-ray sources are also found, adding further evidences of the magnetic reconnection in solar flares. One can note that these observations strongly increases the possibility of seeing the reconnection point in the magnetic neutral sheet. In soft X-ray spectra taken at the very initial phase of flares, completely blueshifted emission lines from hot thermal plasmas are observed, which imply the efficiency of thermal energy transport mechanism of chromospheric evaporation. Further, the entire solar corona is found very dynamic, and numerous X-ray brightenings and/or X-ray jets are discovered. They are also the candidates produced by the magnetic reconnection.