There are two explanations for the broadening mechanisms of the Ca XIX resonance line in the rising phase of a solar flare. One theory relates the line broadening to the velocity dispersion of the chromospheric evaporation along the loop. The other theory attributes the line broadening to nonthermal turbulence resulting from the release of flare energy. We distinguish these two possibilities by studying the influence of the loop orientation on the broadening, based on data from SXT and BCS on Yohkoh. The results seem to indicate that the broadening of the Ca XIX resonance line is caused by nonthermal turbulence.
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