Determination of molecular dissociation rates from measurements of scattered solar ultraviolet light

Abstract

Scattered solar ultraviolet light in the spectral region from 250 to 320 nm was measured from a balloon platform at altitudes ranging from 14.5 to 38.8 km with a wavelength resolution of approximately 0.3 nm and an accuracy in determining the wavelength position of 0.5 nm. We used these scatter data to compare and validate a single scattering model developed for this purpose. Using these semi‐empirical results, we constructed the single scattered component of the ultraviolet irradiance as a function of height and wavelength. From these data, it is possible to determine the percentage dissociation rate of a variety of species due to scattered ultraviolet radiation. These results are presented as a ratio of intensities R = I1/(I0+I1), where I1 is the first order scattering and I0 is the direct attenuated radiation from the sun. The attenuated direct radiation from the sun can be multiplied by the factor 1/(1‐R), the Rayleigh amplification ratio used by Nicolet et al. (1982), to include the contribution to the irradiance from first order scattered light. The results are multiplied by a cross section of the species under consideration to obtain the dissociation rates. Ozone overburden and an approximate ozone particle density altitude profile are obtained when validating the single scatter model.