FLUID-FLOW IN A JET AND THE CA-XIX LINE-PROFILES OBSERVED DURING SOLAR-FLARES

Two types of fluid models were considered as methods for reproducing the blueshifts and line broadening observed in soft X-ray lines during the rise of solar flares. The fluid models representing the laminar flow of material in a jet and through a pipe were used to derive the velocity at each location in the flow. These velocities were then converted to velocity distributions and convolved with a thermal Maxwellian distribution to produce theoretical line profiles. The resulting theoretical profiles were then compared with Ca XIX line profiles observed by SMM's bent crystal spectrometer during the 1980 May 21 flare. Reasonable agreement was found for the jet model, while the pipe model was less successful at reproducing the observed line profiles. The optimal values for the free parameters in the jet model were within the ranges expected for solar flare conditions. The jet was much smaller than typical flare volumes estimated from spatial images, but the resulting densities were consistent with the upper limit of densities derived using density-sensitive line ratios. This supports previous reports of small filling factors and is interpreted as evidence for a chromospheric origin for the flow. Extrapolating back in time indicates that the jet started during the time of the hard X-ray burst. Stability analysis indicates that, although the laminar jet can reproduce the observations, instabilities may cause the flow to become turbulent, and that this laminar treatment is not strictly valid. In conclusion, although the observed line profiles can be explained with multiple blueshifted Gaussians, results from the present work suggest that the continuous velocity distribution within a jet is a viable alternative.