南极高太阳天顶角下地基臭氧总量观测比较分析

Comparison analysis of ground-based total ozone observations under high solar zenith angle at Zhongshan Station, Antarctica

  • 摘要: 我国南极中山站(69.37°S,76.38°E)每年5-7月最低的太阳天顶角(SZA)≥80°,这限制了极夜或接近极夜期间利用太阳直射光(DS)开展大气臭氧柱总量(TOC)的观测,也限制了对秋、冬季乃至全年TOC变化的准确认识。本文对中山站2009~2023年间SZA≥80°时四种TOC测值:资料和方法①Brewer光谱仪DS,②聚焦太阳(FS),③(夜间)聚焦月球(FM)和④SAOZ光谱仪曙暮光,以SZA在 72°~80°时Brewer 光谱仪的DS测值为参考进行比较分析目的。结果显示,结果杂散光使得DS测值在SZA为 81°~81.5°时平均偏低近2%。FS 测值在SZA为 80°~84.5°时平均偏高1.75%,臭氧层质量数(μ)计算值随SZA上升而偏低是FS测值偏高的原因。FM测值平均偏低2.2%。SAOZ测值平均偏低4.4%,曙暮光光程传输几何路径及TOC随纬度上升而上升的分布是SAOZ光谱仪测值偏低的原因。 受极地涡旋驱动的“臭氧洞”期间TOC昼夜急剧变化使得DS,FS和FM测值与参考值间差异大于非“臭氧洞”期间。结论综合四种地基TOC观测可确定:中山站“臭氧洞”开始于8月,极夜期间(6-7月)TOC 均值在270~290DU但最低TOC为~230DU显示臭氧层损耗已经发生,秋季(3月)TOC低值类似于北半球中高纬度9月情形,是南半球平流层Brewer-Dobson环流影响所致。本文建议当SZA≥80°时优先应用FS,而FM是极夜期间唯一有效TOC观测途径。

     

    Abstract: The daily minimum solar zenith angle (SZA)≥ 80° during or near the period of polar night(April-August)at China''s Antarctic Zhongshan Station (69.37°S,76.38°E) restricts the ground-based observations of total ozone column (TOC) by using direct solar light (DS), confining the further accurate understanding of TOC seasonality, especially in the Autumn-winter. In order to overcome the issues, the following four types of TOC observations from 2009 to 2023 at SZA ≥ 80° :①Brewer spectrophotometer DS,TOCDS(≥80°), ②focused sun-disk (FS),TOCFS(≥80°),③focused moon disk (FM),TOCFM and④ SAOZ spectrometer zenith twilight observations, TOCSAOZ, are analyzed referring to the Brewer DS observations within SZA of 72-80°, TOCDS(72°~80°).The results show that TOCDS(≥80°) are on average ( -2.1±4.1(1σ)% or -5.5±9.5 DU, n=1811)lower, TOCFS(≥80°) are average(1.75±4.3(1σ)% or 2.8±4.3 DU ,n=2765)higher. The fixed stratospheric ozone layer height (~22km) in the air mass factor (μ)calculations causes a decrease μ with the rise of SZA is the main reason for the higher TOC FS(≥80°) . TOCFM is average(-2.2±6.8(1σ)% or -6.8±16.7 DU, n=78)lower. TOCSAOZ is average ( -4.4%±5.0(1σ)% or -12.1±12.9 DU, n=1370)lower. The geometry of twilight together with the nature latitudinal distribution of TOC are the reasons for lower TOCSAOZ values. The significant diurnal variation of TOC during the ‘ozone hole’ (TOC ≤ 220 DU) increases the difference between those observed TOC at SZA≥80° and the reference. It is confirmed that annual ‘ozone hole’ at Zhongshan Station starts in August. The average TOC within 270-290 DU with the individual lowest of ~230 DU shows that ozone depletion has already occurred during the polar night (June-July)during which the polar vortex has developed. The secondary lower TOC in autumn (March)which are due to the influence of the nature stratospheric Brewer-Dobson circulation is similar to the Autumn lowest TOC at middle and high latitudes in northern hemisphere. FS observations should be preferentially applied when the SZA ≥ 80°, and FM should be stressed because it is the only effective way during the polar night for the routine TOC observations.

     

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