南极中山站高太阳天顶角时地基臭氧总量观测比较

Comparative of total ozone column observed under high solar zenith angles at Zhongshan station, Antarctica

  • 摘要: 中国南极中山站(69.37°S,76.38°E)每年5—7月最低太阳天顶角(SZA)≥80°限制了利用太阳直射光(DS)开展大气臭氧柱总量(TOC)的观测,进而影响了对秋、冬季乃至全年TOC变化的准确认识。对南极中山站2009—2023年高太阳天顶角(SZA≥80°)时4种(Brewer光谱仪DS即TOCDS (≥80°),聚焦太阳(FS)即TOCFS (≥80°),(夜间)聚焦月球(FM)即TOCFM和SAOZ曙暮光光谱仪即TOCSAOZ)观测值以SZA在72°,80°)时Brewer 光谱仪的DS观测值(TOCDS72,80°))为参考进行了比较。结果显示,杂散光使得TOCDS (≥80°)观测值在SZA为81°,81.5°)时平均差异和相对差异分别偏低(5.5±9.5(1σ)) DU和( 2.1±4.1(1σ))%;TOCFS (≥80°)观测值在SZA为 80°,84.5°)时平均差异和相对差异分别偏高(2.8±4.3(1σ)) DU和(( 1.75±4.3(1σ))% ,臭氧层质量数(μ)随SZA增大而偏低是TOCFS (≥80°)观测值偏高的原因;TOCFM观测值平均差异和相对差异分别偏低(6.8±16.7(1σ)) DU和 (2.2±6.8(1σ))%,TOCSAOZ 对应的差异则分别偏低( 12.1±12.9(1σ))DU 和 ( 4.4%±5.0(1σ)) % 。曙暮光在大气中较长传输光程及TOC随纬度增高而增大导致了TOCSAOZ明显偏低。“臭氧洞”期间TOC昼夜急剧变化造成DS、FS和FM观测值与参考值的差异大于非“臭氧洞”期间。建议SZA≥80°时优先应用FS观测,FM是极夜期间唯一有效TOC观测途径。综合4种高SZA情形下的地基TOC观测可确定:南极中山站“臭氧洞”开始于8月,极夜期间TOC 均值270—290 DU,最低约为230 DU,表明臭氧层损耗已经发生;秋季(3月)TOC低值与北半球中高纬度9月情形相似,是南半球平流层Brewer-Dobson环流影响所致。

     

    Abstract: Daily minimum solar zenith angle (SZA)≥80° during or near the period of polar night (May-July) at Zhongshan station of China (69.37°S, 76.38°E) in Antarctic restricts ground-based observations of total column (TOC) by using direct solar light (DS), which limits further accurate understanding of TOC seasonality, especially in the autumn and winter. To address this issue, the following four types of TOC observations at SZA≥80°: ① Brewer ozone spectrophotometer DS, TOCDS (≥80°), ② focused sun-disk (FS), TOCFS (≥80°), ③ focused moon disk (FM), TOCFM and ④ SAOZ spectrometer zenith twilight observations, TOCSAOZ, made from 2009 to 2023 are analyzed with reference to the Brewer DS observations within SZA of 72°, 80°), i.e., TOCDS (72, 80°)).The results show that, on average, TOCDS(≥80°) are lower by (5.5±9.5(1σ)) DU or (2.1±4.1(1σ)) % when SZA is 81°, 81.5°) while TOCFS (≥80°) are higher by (2.8±4.3(1σ)) DU or (1.75±4.3(1σ))% when SZA is 80°, 84.5°) . The fixed stratospheric ozone layer height (~22 km) in the air mass factor (μ) calculation causes a decreased μ with increasing SZA, which is the main reason for the higher TOC FS (≥80°) . On average, TOCFM is lower by (6.8±16.7(1σ)) DU or (2.2±6.8(1σ))% while TOCSAOZ is lower by (12.1±12.9(1σ)) DU or (4.4%±5.0(1σ))% on average. The longer optical path of twilight in the atmosphere 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) period increases the differences between those observed TOC at SZA≥80° and the reference. It is confirmed that the annual 'ozone hole' at Zhongshan Station starts in August. The average TOC is within 270—290 DU while the minimum value can be ~230 DU, indicating that ozone depletion has already occurred during the polar night when the polar vortex has developed. The secondary seasonal lower TOC in autumn (March), which are due to the influence of the nature stratospheric Brewer-Dobson circulation, is similar to the lowest TOC in autumn in the middle and high latitudes of the northern hemisphere. FS observations should be preferentially applied when the SZA≥80°, and FM should be implemented because it is the only effective way during the polar night for routine TOC observations.

     

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