Results of four numerical simulations of convective thin cirrus are presented. Midday and nighttime cases at subtropopause (-60¿C) and lower (-35¿C) levels are considered. Each case is weakly forced by large-scale ascent. Radiative processes are shown to strongly regulate the convective structure and ice water budget of the cloud (30% denser at night). Day-night differences result primarily from radiative modulation of buoyancy and the resultant differences in the organization of convection. The nature of this coupling between radiative processes and cloud circulations is discussed. The direct effects of radiative heating or cooling on the saturation vapor pressures are found to be of secondary importance in these convective cases. ¿American Geophysical Union 1987