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

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.