Radiative transfer numerical simulations have been made for quantitatively analyzing the effect of ozone depletion on solar irradiance at the Earth's surface in the UV and visible ranges. Simulations show that ozone's temperature-dependent absorption and atmospheric multiple scattering play important roles in the UV region. By means of sensitivity analyses, the level of surface UV-B irradiance under clear-sky conditions is shown to depend, with a decreasing significance, on solar zenith angle, total column ozone, surface spectral reflectivity, stratospheric temperature, and aerosol variations. The simulation results are compared with the National Science Foundation (NSF)/UV spectroradiometer data obtained at Plamer Station on the Antarctic Peninsula and the Total Ozone Mapping Spectrometer (TOMS) satellite data. In general, the model and data show good agreement, especially in the UV region. Based on simulation results, we develop a UV irradiance ratio method to estimate total column ozone from the NSF/UV spectroradiometer using clear-sky data obtained during the austral spring of 1988 and 1990. A method for estimating surface UV-B from TOMS satellite data is also developed. The ATRAD model provides a basis for the accurate estimation of the ratios of UV-B (280--320 nm) to UV-A (320--400 nm) to photosynthetic available radiation (PAR, 400--750 nm) for ecological studies concerned with the biological effects of ozone depletion over the Antarctic. ¿ American Geophysical Union 1992