Comparison of Solar Ultraviolet Irradiance Measurements at Zhongshan Station, Antarctica

A comparative analysis is presented on surface solar ultraviolet B (UVB) band and ultraviolet A (UVA) irradiance measured by 3 UV broadband pyranometers: FSUVA(315-400 nm), FSUVB(280-315 nm) provided by Jiangsu Radio Scientific Institute Co. LTD (CJRSI), American Yankee UVB(280-320 nm), and Brewer ozone spectrophotometer, placed at Zhongshan Station, Antarctica. Using data of Brewer ozone spectrophotometer in 2017 as a reference, results show that, for UVB(280-315 nm) irradiance, the error of FSUVB is averagely (55±75)% but its irradiance is lower during the "ozone hole" period, indicating that domestic made FSUVB broadband radiometer is less sensitive to the ozone layer thinning. Furthermore, the irradiance relative error of FSUVB shows a certain upward trend with the increase of total atmospheric ozone, indicating an over-measured UVB irradiance by the FSUVB pyranometer in regions with normal ozone concentration, such as the area of middle-low latitudes including China. As a contrast, the error of Yankee UVB (280-320 nm) is averagely (-31±22)% lower than that of Brewer measured, however, the relative error and total ozone variation are unrelated. The under-measured UVB irradiance from the Yankee UVB pyranometer is attributed to the system calibration error. Since Brewer spectral UV measurement is limited within 286.5-363 nm, a so-called UV correction factor, on the basis of empirical ratio of spectral irradiance at the wavelength longer than 363 nm to the Brewer measured irradiance at 363 nm, is applied to make up Brewer spectral irradiance gap of 363.5-400 nm with wavelength resolution of 0.5 nm for constructing Brewer entire spectral UVA (315-400 nm) irradiance. The error of FSUVA is averagely (23±59)% when Brewer UVA irradiance is used as the reference. With tropospheric Ultraviolet visible (TUV) radiation model calculations under cloud-free and the sun zenith angle (SZA)less than 80° as references, irradiance errors measured by FSUVB, Yankee UVB and FSUVA are (30±37)%, (-22±19)% and (27±6.4)%, respectively, in 197 cases, while the average of differences between Brewer and TUV calculations are respectively (3.4±8.5)% in UVB band of 286.5-315 nm, (2.9±6.8)% in UVB band of 286.5-320 nm and (3.4±4.5)% in UVA band of 315-400 nm, proving the method of Brewer UVA correction factor is rational. Again, only the relative error of FSUVB measurements referenced to TUV calculations displays an evident increasing trend with the growth of total ozone. Mechanisms of over-measured solar irradiances from both domestic made broad-band UV pyranometers are not fully identified. Calibration methods needed to be improved with consideration of variable SZA and total ozone. In addition, the stray light at longer wavelengths should have a significant influences on the pyranometer's performances and this stray light need to be eliminated in further instrument improvement. For FSUVB, its less sensitiveness to the solar UVB irradiance during the period of "ozone hole" still needs to be resolved.