Stratospheric measurements of collision‐induced absorption by molecular oxygen

Abstract

Collision‐induced absorption by the fundamental vibration‐rotation band of O2 has been studied in high‐resolution (0.02 cm−1) stratospheric solar absorption spectra. The data were recorded during sunset with the University of Denver balloon‐borne interferometer from a float altitude of 33 km. The O2 continuum has been identified in the 1400–1700 cm−1 region in spectra obtained at tangent altitudes below 22 km. Measurements of transmittances in narrow intervals nearly free of atmospheric line absorption are in good agreement with values calculated with the O2 absorption coefficients as compiled by Timofeyev and Tonkov (1978). Absorption by other atmospheric species (primarily from wings of strong H2O lines) contributes only a small fraction of the total absorption at the measured frequencies. The measurements indicate an upper limit of 20% for the uncertainty of the available O2 absorption coefficients at lower stratospheric temperatures (≈220 K).