The afternoon auroral emissions are investigated in the equinoxes for geomagnetically quiet conditions (Kp = 1) using auroral images from ultraviolet imager (UVI) aboard the Polar satellite. They are compared with solar illumination effects (the solar zenith angle [SZA] and the consequent ionospheric conductivity) and the dipole tilt angle, as well as the observational region 1 upward field-aligned currents (FACs) from AMPERE data. The averaged afternoon auroral emissions have pronounced universal time (UT) variations with valley (2.8 photons/cm²/s) at around 01:00–03:00 UT and peak (4.7 photons/cm²/s) at around 17:00–19:00 UT. They generally vary with the solar illumination, the dipole tilt angle and the observed region 1 upward FACs as a function of UT. The afternoon auroral intensity is anticorrelated with the SZA and positively proportional to the solar EUV-produced Pedersen conductivity, region 1 upward FACs and dipole tilt angle. Additionally, they depend weakly on solar flux under geomagnetically quiet conditions. These results suggest that in the afternoon auroral region, the peak auroral emissions are closely associated with the peak conductivity and the maximum upward FACs. Other mechanisms, such as the dipole tilt angle, may also contribute. Further comparison between the northern afternoon aurora and the FACs in the two conjugate hemispheres suggests little contributions on the auroral UT variations from the interhemispheric FACs in the equinoxes.

中文翻译：

---

春分季节午后极光强度的世界时变化

使用极地卫星上紫外线成像仪 (UVI) 的极光图像，在地磁安静条件 (Kp = 1) 的春分点研究了下午的极光发射。它们与太阳光照效应（太阳天顶角 [SZA] 和随之而来的电离层电导率）和偶极子倾斜角，以及来自 AMPERE 数据的观测区域 1 向上场对齐电流 (FAC) 进行了比较。平均下午极光排放具有显着的通用时间与谷（UT）的变化（2.8光子/厘米² /秒）在约01：00-03：00 UT和峰（4.7光子/厘米²/s) 在 17:00–19:00 UT 左右。它们通常随着太阳光照度、偶极子倾斜角和观察到的区域 1 向上 FAC 作为 UT 的函数而变化。下午的极光强度与 SZA 反相关，与太阳 EUV 产生的 Pedersen 电导率、区域 1 向上的 FAC 和偶极子倾斜角成正比。此外，在地磁安静的条件下，它们对太阳通量的依赖较弱。这些结果表明，在下午的极光区，极光发射峰值与电导率峰值和最大向上 FAC 密切相关。其他机制，例如偶极子倾斜角，也可能有贡献。