HIGH-RESOLUTION ANALYSIS OF DIRECT AND SCATTERED RADIATION IN THE STRATOSPHERE BETWEEN 175 AND 210 NM

Direct and scattered components of solar radiation in the stratosphere are examined at wavelengths between 175 and 210 nm, Absorption by oxy gen in the Schumann-Runge system is treated exactly using temperature dependent cross sections at a spectral resolution of 0.5 cm-1 (almost- equal-to 0.002 nm). Consistent with previous studies employing spectra lly averaged cross sections, the calculated ratio of scattered to dire ct flux is more than a factor of 2 smaller than observed below 21 0 nm . The flux ratio is constrained above a minimum value at large opaciti es due to a twilight effect, occurring when the attenuation of scatter ed light from overhead paths is not as great as over the slant path of the direct beam; however, this phenomenon alone cannot account for ob servations. An improved description of scattering by O2 for wavelength s below 200 nm is presented which includes effects of incoherent scatt ering. Use of the revised parameters for oxygen scattering does not br ing the calculated flux ratios into agreement with observations, but d oes lead to small changes in the scattered field and O2 photodissociat ion rate below 190 nm.