The ratio of O number density to N₂ number density (O/N₂) is an important parameter to describe thermospheric composition changes and its effects on the ionosphere. Based on Global Ultraviolet Imager (GUVI) limb measurements, we investigate the seasonal behaviors of O/N₂ volume density ratio on different constant pressure levels during geomagnetically quiet periods. The global O/N₂ shows the prominent annual and semiannual variations with solar activity dependence. An empirical model considering the solar activity and annual/semiannual variations can reasonably reproduce the original O/N₂. The modeled O/N₂ captures the hemispheric asymmetry of the annual variations in both length and magnitude. Global maps of the seasonal harmonic components of the modeled O/N₂ indicate the latitudinal and altitudinal dependence of O/N₂ seasonal variations. The annual component dominates over the semiannual component at mid‐latitudes, but it is smaller than the semiannual component at low latitudes. In the Northern Hemisphere, and at low geomagnetic latitudes of the Southern Hemisphere, the annual component peaks around December solstice at all altitudes, whereas at middle geomagnetic latitudes of the Southern Hemisphere, it peaks around June solstice. The semiannual component peaks at the equinoxes in almost all regions over the globe at all altitudes. The annual and semiannual amplitudes both increase with altitude. In addition, O/N₂ annual variations and solar activity dependence are more influenced by the thermal expansion and contraction.

中文翻译：

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GUVI肢体测量结果显示不同压力水平下O / N2的季节变化

O数密度与N ₂数密度之比（O / N ₂）是描述热层组成变化及其对电离层影响的重要参数。基于全球紫外线成像仪（GUVI）肢体测量，我们研究了地磁安静期间O / N ₂体积密度比在不同恒定压力水平下的季节性行为。全球O / N ₂随太阳活动的依赖关系显示出显着的年度和半年度变化。考虑太阳活动和年度/半年度变化的经验模型可以合理地再现原始的O / N ₂。建模的O / N ₂捕获了长度和幅度每年变化的半球不对称性。全局映射建模的O季节性谐波分量的/ N ₂表示的O / N的纬度和海拔高度的依赖₂季节变化。在中纬度地区，年度分量占主导地位，但在低纬度地区，年度分量要小于半年度分量。在北半球和南半球的低地磁纬度下，年分量在所有海拔高度都在12月夏至左右达到峰值，而在南半球的中地磁纬度则在6月冬至左右达到峰值。半年度分量在全球所有海拔的几乎所有区域的均分点达到峰值。年度和半年度振幅都随高度增加。另外，O / N ₂年变化和太阳活动依赖性受热膨胀和收缩的影响更大。