Variability and trends in surface solar spectral ultraviolet irradiance in Italy: on the influence of geopotential height and lower-stratospheric ozone

Abstract. The short- and long-term variability of the surface spectral solar ultraviolet (UV) irradiance is investigated across Italy using high-quality ground-based measurements from three locations: Aosta (45.7? N, 7.4? E, 570 m a.s.l.), Rome (41.9? 12.5? 15 75 Lampedusa (35.5? 12.6? 50 a.s.l.). sites are characterized by different environmental conditions represent almost full latitudinal extent Italian territory. Data two periods were analysed: 2006–2020 (all sites) 1996–2020 (Rome only). main objective this study to quantify effect geopotential height (GPH) at 250 hPa on total ozone, 307.5 324 nm. We first show that monthly anomalies in GPH, irradiances correlated amongst sites, suggesting often affected same synoptical weather systems. further find statistically significant anticorrelations between GPH ozone for all stations months. Conversely, we identify positive correlations nm most influence short-term also hold trends. For example, changes over period associated with stations. This suggests observed negative trends mainly driven lower-stratospheric as upper-stratospheric was increasing period. several months year, UV observed, found these predominantly caused clouds and/or aerosols instead ozone. longer 1996–2020, a annualized decrease ? 0.1 % per year identified could subsequently be attributed decreasing While extended period, trend did not lead deseasonalized data. Our provides evidence dynamical processes taking place troposphere irradiance.