Preprints
https://doi.org/10.5194/acp-2021-616
https://doi.org/10.5194/acp-2021-616

  02 Sep 2021

02 Sep 2021

Review status: this preprint is currently under review for the journal ACP.

Variability and trends of the surface solar spectral ultraviolet irradiance in Italy: a possible influence of lower and upper stratospheric ozone trends

Ilias Fountoulakis1,a, Henri Diémoz1, Anna Maria Siani2, Alcide di Sarra3, Daniela Meloni3, and Damiano M. Sferlazzo4 Ilias Fountoulakis et al.
  • 1Aosta Valley Regional Environmental Protection Agency (ARPA), 11020 Saint-Christophe, Italy
  • 2Physics Department, Sapienza Università di Roma, 00185 Rome, Italy
  • 3ENEA, Laboratory for Earth Observations and Analyses, 00123, S. Maria di Galeria, Rome, Italy
  • 4ENEA, Laboratory for Earth Observations and Analyses, 92010, Lampedusa, Italy
  • anow at: Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing, National Observatory of Athens (IAASARS/NOA), 15236 Athens, Greece

Abstract. In this study the short- and long-term variability of the surface spectral solar ultraviolet (UV) irradiance are investigated over Italy using high quality ground based measurements from three sites located at quite different environmental conditions, and covering the full latitudinal extent of the Italian territory: Aosta (45.7° N, 7.4°  E, 570 m a.s.l.), Rome (41.9° N, 12.5° E, 75 m a.s.l.), and Lampedusa (35.5° N, 12.6° E, 50 m a.s.l.). The variability of the irradiances at 307.5 nm, 324 nm, and of the ratio between the 307.5 nm and the 324 nm irradiances were investigated with respect to the corresponding variability in total ozone and the geopotential height at 250 hPa (GPH). The study was performed for two periods: 2006–2020 for all stations, and 1996–2020 only for Rome. A statistically significant correlation between the GPH and total ozone monthly anomalies was found for all stations and all seasons of the year. A corresponding statistically significant correlation was also found in most cases between the GPH and the 307.5 nm irradiance monthly anomalies. The correlation between GPH anomalies at different sites was statistically significant, possibly explaining the strong and significant correlation between the total ozone monthly anomalies at the three sites. A statistically significant decrease of total ozone, of ~0.1 %/year was found for Rome for the period 1996–2020, which however did not induce increasing trends in irradiance at 307.5 nm (neither increasing trends in the ratio between the 307.5 nm and the 324 nm irradiances) at SZA = 67°. Further analyses revealed positive trends in the ratio and the 307.5 nm irradiance at smaller solar zenith angles (SZA), which can be attributed to the fact that total ozone decrease is driven by a decrease in the lower stratosphere while upper stratospheric ozone increases, and the effect of changes of upper stratospheric ozone becoming disproportionately larger for increasing SZA. It was also showed that long-term changes in total ozone follow changes in GPH, which is an additional indication that negative trends in total ozone are mainly driven by changes in lower stratospheric ozone. An anti-correlation between the GPH long-term changes and total ozone was also evident for all stations in 2006–2020. Positive trends in UV irradiance for this latter period which were possibly driven by changes in clouds and/or aerosols were found for Rome and Aosta. This study clearly points out the significance of dynamical processes which take place in the troposphere for the variability of total ozone and surface solar UV irradiance.

Ilias Fountoulakis et al.

Status: open (until 14 Oct 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'The description of the effect of the ozone profile on UV radiation should be modified', Anonymous Referee #1, 18 Sep 2021 reply

Ilias Fountoulakis et al.

Ilias Fountoulakis et al.

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Short summary
The variability and trends of solar spectral ultraviolet irradiance have been studied for the periods 1996–2020 (for Rome) and 2006–2020 (for Lampedusa, Rome, and Aosta) with respect to the variability and trends of total ozone, and dynamical tropospheric processes. Analyses revealed increasing UV at Rome and Aosta, which is possibly due to decreasing lower stratospheric ozone, and decreasing attenuation by aerosols and/or clouds.
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