The polar twilight atmosphere is different from that at mid-latitude in several ways which lead to significant changes in the wave-length-dependent radiation field. Ozone depletion in the stratosphere leads to increased scattering below 340 nm. Polar stratospheric clouds produce changes in the radiation field which depend on cloud height and thickness. A surface albedo near unity produces a larger increase in scattering. Multiple scattering becomes a large percentage of the radiation field as solar zenith angle increases. These perturbations on the radiation field lead to enhanced ozone destruction in the stratosphere, increased surface irradiance, and a significant wavelength-dependent increase in nadir radiance. ¿ American Geophysical Union 1990