THE EFFECTS OF HORIZONTALLY EXTENDED CLOUDS ON BACKSCATTERED ULTRAVIOLET SUNLIGHT

This work examines the effects of clouds on backscattered ultraviolet radiation via analysis of satellite observations and radiative transfe r modeling. Measurements from the continuous scan mode of the Nimbus 7 SBUV instrument show that the enhancement in backscatter albedo assoc iated with clouds generally increases with wavelength. However, high c louds enhance the backscattered ultraviolet radiation at short wavelen gths more than do low or middle level clouds. For an overhead Sun in t he tropics, the enhancements in backscattered radiance from high cloud s are about 5 times those from low clouds at a wavelength of 300 nm. F or a typical mid-latitude atmosphere with a solar zenith angle of 60 d egrees, the enhancements in backscattered radiance from high clouds ar e approximately double those due to low level clouds.