INFLUENCE OF LINE MIXING ON ABSORPTION BY CO2 Q-BRANCHES IN ATMOSPHERIC BALLOON-BORNE SPECTRA NEAR 13 MU-M

Line mixing in CO2 Q branches is studied in the 13.2 mu m region from balloon-borne atmospheric transmission measurements. Eighty-five spect ra were recorded (at 67 degrees N, 22 degrees E) in the 660-960 cm(-1) region using a Fourier transform spectrometer with an unapodized reso lution (full width at half maximum) of 0.013 cm(-1). They involve ball oon altitudes and tangent heights from 13 to 30 km and a large range o f optical thicknesses. The results of computations assuming Voigt line shapes as well as accounting for line mixing are compared with measur ed transmissions in three CO2 Q branches of different intensities and symmetries. They confirm the significant effect of line mixing and val idate recent line coupling models. As a consequence of the accuracy of the forward approach the Q branches can be used for remote sensing; t his should lead to improved precision of pressure/temperature retrieva ls since absorption in the Q branch wing region is particularly pressu re sensitive.