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We report on radiative hydrodynamic simulations of moderate and strong solarflares. The flares were simulated by calculating the atmospheric response to abeam of non-thermal electrons injected at the apex of a one-dimensional closedcoronal loop, and include heating from thermal soft X-ray, extreme ultravioletand ultraviolet (XEUV) emission. The equations of radiative transfer andstatistical equilibrium were treated in non-LTE and solved for numeroustransitions of hydrogen, helium, and Ca II allowing the calculation of detailedline profiles and continuum emission. This work improves upon previoussimulations by incorporating more realistic non-thermal electron beam modelsand includes a more rigorous model of thermal XEUV heating. We find XEUVbackwarming contributes less than 10% of the heating, even in strong flares.The simulations show elevated coronal and transition region densities resultingin dramatic increases in line and continuum emission in both the UV and opticalregions. The optical continuum reaches a peak increase of several percent whichis consistent with enhancements observed in solar white light flares. For amoderate flare (~M-class), the dynamics are characterized by a long gentlephase of near balance between flare heating and radiative cooling, followed byan explosive phase with beam heating dominating over cooling and characterizedby strong hydrodynamic waves. For a strong flare (~X-class), the gentle phaseis much shorter, and we speculate that for even stronger flares the gentlephase may be essentially non-existent. During the explosive phase, syntheticprofiles for lines formed in the upper chromosphere and transition region showblue shifts corresponding to a plasma velocity of ~120 km/s, and lines formedin the lower chromosphere show red shifts of ~40 km/s.Comment: 21 pages, 15 figures. Will appear in 2005 September 1 issue of the  Ap

Radiative Hydrodynamic Models of the Optical and Ultraviolet Emission from Solar Flares