On the response of the atomic oxygen red line emission rates to the Sun's energy input: an empirical model deduced from WINDII/UARS global measurements

Abstract

In a previous paper by Zhang and Shepherd, an empirical model for the peak volume emission rate (Vp) and the integrated volume emission rate of the O(1D) (630 nm) dayglow was deduced from more than 130,000 daytime emission rate profiles observed by the Wind Imaging Interferometer (WINDII) on the Upper Atmospheric Research Satellite (UARS) during 1991-1995. In the model, the emission rates are given as functions of the solar zenith angle (χ) and solar irradiance using the F10.7 cm flux as a proxy. This paper extends the daytime empirical model into the twilight zone and includes the height of the peak emission rate and the width of the emission layer. For a given day, the O(1D) emission layer during both daytime and twilight-time is found to be sensitive to the solar zenith angle when solar irradiance is treated as a constant. Positive linear relationships are found between the daytime emission rate and cos1/eχ at χ < 87° the twilight-time emission rate and cos(χ+0.25)1.8 at 87° less than or equal to χ less than or equal to 104.5°, and the width of the emission layer and cosχ at χ < 87°. A negative linear relationship is found between the peak emission rate and its height at χ < 104.5°. In the long-term, the emission layer varies according to the solar cycle in that both the emission rate and the height of the emission layer increase with increasing solar irradiance. The empirical model provides the peak volume emission rate and its height, and the integrated emission rate, for both daytime and twilight zones, and the width of the daytime emission layer as functions of the solar zenith angle and solar irradiance using F10.7, E10.7, and Lyman-β as proxies. The profiles of the volume emission rate and global morphology of the red line emission therefore can be constructed using the model. Effects of solar storms, and physical precesses and photochemical reactions other than that due to the direct solar energy deposition in the thermosphere can be derived by comparing to the model.