Reconciling Hydrodynamic Simulations with Spectroscopic Observations of Solar Flares

Chromospheric evaporation is a central element of current models of solar flares. The high-velocity upflows that should accompany evaporation, however, are rarely observed in high-resolution solar flare spectra. Thus the absence of blueshifted line profiles represents a significant discrepancy between the theory and observations of this phenomenon. In this Letter we present an algorithm for computing multiple-loop time-dependent hydrodynamic simulations of solar flares using a minimum of assumptions. We show that these simulations can accurately reproduce the Ca XIX and S XV line profiles observed with the Bragg Crystal Spectrometer on Yohkoh during the earliest stages of a flare. Since our model represents the flare as a succession of independently heated threads, the strongly blueshifted emission evident during the initial heating of a thread is largely masked by emission from threads that have been heated previously and do not show bulk motions.