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

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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.