ROCKET OBSERVATIONS OF OXYGEN NIGHT AIRGLOWS - EXCITATION MECHANISMS AND OXYGEN ATOM CONCENTRATION

The altitude profiles of oxygen night airglows were observed by rocket experiments at Uchinoura (31-degrees-N). Simultaneous measurements of emission rates at three different bands of the O2 Herzberg I system, originating from higher, middle and lower vibrational levels of O2(A3SIGMA(u)+), suggests that the vibrational distribution of O2(A3SIGMA(u)+) is almost invariant in the night airglow and that it varies considerably in the rocket glow. This result is explained by a model for the excitation and de-excitation of the Herzberg I system, where O2(A3SIGMA(u)+) is assumed to be excited directly in the three-body recombination of oxygen atoms and to be de-excited mainly due to collisions with atmospheric molecules. A possible range of the rate coefficients of the O2(A3SIGMA(u)+) de-excitation is determined to be compatible with the observation. Based on the inferred excitation mechanisms, oxygen atom concentration is deduced from the observed emission rates of the Herzberg I bands within a systematic error of factor 2 approximately 4 in terms of its absolute value and within an error around 20 % in terms of its relative value. The OI green line airglow at 557.7 nm and the O2 Infrared Atmospheric (0,0) band airglow at 1.27 mum were observed simultaneously with the Herzberg I bands, and their excitation mechanisms axe also discussed. The excitation mechanism of the green line is confirmed to be the two-step process. The O2 Infrared Atmospheric system is excited via the three-body recombination of oxygen atoms in an altitude region above approximately 90 km, whereas it is likely to be excited mostly by another mechanism below approximately 90 km.