Soft X-ray flare dynamics

We discuss the dynamics of four soft X-ray flares as revealed by the X-ray resonance line profiles of the He-like ions, Fe XXV, Ca XIX, and S XV. The flares chosen for analysis belong to a subclass of events that have intense Doppler blueshifted spectral signatures during the rise phase. The spectra were obtained from the Bragg crystal spectrometer (BCS) experiment flown on the Japanese Yohkoh spacecraft. We deconvolve the line profiles into a flare decay phase component (stationary component) produced by nonmoving plasma with little or no turbulent motions, and a flare rise phase component (dynamic component) produced by bulk plasma motion and turbulence. The dynamic component is further deconvolved into a high-speed component (greater than 400 km s(-1)) and a lower speed, more turbulent component, We find that the dynamic and stationary components have approximately the same electron temperature. The dynamic and stationary component fluxes are compared with hard X-ray fluxes obtained from the hard X-ray telescope (HXT) on Yohkoh. We find that the onset time of the high-speed dynamic component corresponds closely to the onset of hard X-rays. We discuss the X-ray morphology of the flares as revealed by the soft X-ray telescope (SXT) and hard X-ray telescope (HXT) on Yohkoh. From analysis of the X-ray light curves of individual pixels in the SXT images, we believe we have been able to determine at least some of the locations of the dynamic component in the images. Although the observations support many aspects of chromospheric evaporation models, there are significant problems. No obvious rising fronts of plasma are observed for any of the flares. There are apparent footpoint hard X-ray sources that cannot be physically related in an obvious manner with the main sources of soft X-ray emission. The flares are complex, and therefore there are some ambiguities in interpretation of the morphology.