Abstract. Ground-based observations show a phase shift in semi-annual variation of excited hydroxyl (OH*) emissions at mid-latitudes (43° N) compared to those at low latitudes. This differs from the annual cycle at high latitudes. We examine this behaviour utilising an OH* airglow model which was incorporated into the 3D chemistry-transport model (CTM). Through this modelling, we study the morphology of the excited hydroxyl emission layer at mid-latitudes (30° N–50° N), and we assess the impact of the main drivers of its semi-annual variation: temperature, atomic oxygen, and air density. We found that this shift in the semi-annual cycle is determined mainly by the superposition of annual variations of temperature and atomic oxygen concentration. Hence, the winter peak for emission is determined exclusively by atomic oxygen concentration, whereas the summer peak is the superposition of all impacts, with temperature taking a leading role.

中文翻译：

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中纬度地区兴奋性羟基排放量的半年变化

摘要。地面观测显示，与低纬度地区相比，中纬度地区（43°N）的激发羟基（OH *）排放半年变化具有相移。这与高纬度地区的年度周期不同。我们使用OH *气辉模型检查了此行为，该模型已合并到3D化学传递模型（CTM）中。通过此模型，我们研究了中纬度（30°N–50°N）激发的羟基发射层的形态，并评估了其半年变化的主要驱动因素的影响：温度，原子氧和空气密度。我们发现半年周期的这种变化主要由温度和原子氧浓度的年变化的叠加决定。因此，冬天的排放峰值完全取决于原子氧浓度，