Aurora and diurnal tides in the daytime O(1S) emission rates from WINDII/UARS measurements

Abstract

In a previous study by Zhang and Shepherd, an empirical model for the daytime (sunlit) O( 1 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( 1 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.