Spectral measurements of surface solar irradiance in the ultraviolet are conducted at the Laboratory of Atmospheric Physics (LAP), Aristotle University of Thessaloniki (AUTH), Greece, since the early 1990s, using a double- and a single-monochromator Brewer spectrophotometers. The quality of the measurements is ensured by the application of the well-established LAP/AUTH quality control protocols and is enhanced by the parallel operation of the two instruments via consistency checks of their synchronous measurements. The variability of spectral UV irradiance measured at LAP/AUTH at selected wavelengths for the period 1990–2021 at different time scales is discussed, in association with observed changes in total ozone, aerosol optical depth and clouds. The extended time series of measurements, generally, reconfirms the increasing tendency in UV irradiance reported in previous studies (e.g., Fountoulakis et al, 2016). Positive long-term changes in monthly mean anomalies, of 5–7 % per decade, have been detected at UV-B wavelengths, both under clear- and all-sky conditions. The main factor explaining the clear-sky changes is the decreasing aerosol amount and absorption efficiency, and for the all-sky data decreases in cloudiness. The analysis is extended to the investigation of the seasonal and spectral effect of the changes, as well as to the assessment of their statistical significance.

Garane K., I. Fountoulakis, A. Karanikolas, A. F. Bais, C. Meleti

AIP Conf. Proc. 18 January 2024; 2988 (1): 090003,2024