Twilight OI 6300 A airglow measurement using a high dispersion monochromator

The OI 6300 A airglow in the morning twilight was observed with a high dispersion Ebert spectrometer. The 6300 A emission could be detected against the background continuum due to Rayleigh scattering of the solar radiation with good accuracy for the solar zenith angle (SZA) larger than 960. The O2 photodissociation may be the main excitation process for SZA = 1020--980; a theoretical calculation based on this excitation process can reproduce the observed 6300 A intensity. The emission intensity observed shows a long-term variation in correlation with the solar activity, which may be caused by the variation of the thermospheric O2 density due to the variation of the thermopause temperature. A seasonal variation of the emission intensity, which shows large enhancement in winter, would be ascribed to the additional excitation by the local and conjugate photoelectron. (auth.)