In a previous study by Zhang and Shepherd, an empirical model for the daytime (sunlit) O(<sup>1</sup>S) green line emission layer was deduced using more than 520,000 emission rate profiles observed by he Wind Imaging Interferometer (WINDII) on the Upper Atmospheric Research Satellite (UARS) during 1991-1997. In the model, the peak emission rates and their altitudes, and the widths of both the F-layer and the E-layer of the emission are given as functions of the solar zenith angle χ and solar irradiance using F10.7 as a proxy. With this model, the daytime emission rate directly related
to χ and solar irradiance can be calculated and removed, resulting in the residual emission rates. In this paper, the residual emission rates are presented in both geographic and geomagnetic latitude and local time coordinates grouped by seasons and Kp values. The main results are as follows. (1) The residual emission rates show a midday enhancement at the equator and midday depletions at mid-latitudes in the E-layer. Those variations may be attributed to the diurnal tide. The midday equatorial enhancement also occurs in the F-layer. (2) There is a deep gap in the E-layer at 35°S-65°S at the June solstice, which is wider in the morning than in the afternoon when Kp is low, and vice versa when Kp is high.
(3) At latitudes poleward of 50° the daytime O(<sup>1</sup>S) aurora is conspicuously displayed in geomagnetic coordinates in both layers even for days with low Kp values, peaking at 60-70° geomagnetic latitudes and in the morning sector or in the afternoon sector or both depending on seasons. The aurora is significantly enhanced when Kp is increased. (4) There is a midday (geomagnetic noon) gap at high latitudes in both layers with a width of 3-4 hours. The gap is deepened when Kp is increased. (5) The integrated volume emission rates have similar features at high latitudes to those seen in the peak volume emission rates.
In a previous paper by Zhang and Shepherd, an empirical model for the peak volume emission rate (<i>V<sub>p</sub></i>) and the integrated volume emission rate of the O(<sup>1</sup>D) (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(<sup>1</sup>D) 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 cos<sup>1/e</sup>χ at χ < 87° the twilight-time emission rate and cos(χ+0.25)<sup>1.8</sup> 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.