UK-Japan Cooperative Study of Solar Flares with the SOLAR-A Spacecraft

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The Yohkoh mission was launched in 1991 for the observation of solar flares with a coordinated set of instruments in X-rays and gamma-rays. The Brag crystal spectrometer(BCS) on Yohkoh has an order of magnitude increased sensitivity with less weight and size, if it is compared to the spectrometers flown in the previous solar activity maximum. The instrument was designed and manufactured under the Anglo-Japanese cooperation. The main scientific goal of this instrument is to observe the plasma motions and the transient heating and particle acceleration of flaring plasma at the initial phases of solar flares. The scientific analyses of the Yohkoh data have been done by solar physicists of the both countries. The completely blueshifted emission line was found in the very beginnings of flares. This new discovery supports the hypothesis of chromospheric evaporation. The sulphur emission from solar active regions suggests a possibility of the microflare heating of active regions. The solar corona is very dynamic and many kinds of activity take place as the result of magnetic reconnection.