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.

Highlights

  • The amount of solar ultraviolet radiation (UVR) reaching the Earth’s surface is an important environmental, ecological, and atmospheric parameter to be measured and studied

  • The increase in the 307.5 nm irradiance due to a 1 m increase in geopotential height (GPH) ranged between 0.01 % and 0.1 % depending on season and station

  • The variability of solar UV irradiance at 307.5 and 324 nm and the 307.5/324 nm ratio was analysed with respect to the variability of total ozone and GPH

Read more

Summary

Introduction

The amount of solar ultraviolet radiation (UVR) reaching the Earth’s surface is an important environmental, ecological, and atmospheric parameter to be measured and studied. Dynamical phenomena occasionally (once every few years) favour extensive destruction of Arctic stratospheric ozone in early spring (Dameris et al, 2021; Manney et al, 2011; Pommereau et al, 2018; Varotsos et al, 2012; Wohltmann et al, 2020), leading to reduced ozone over Northern Hemisphere high latitudes and midlatitudes (due to the transport of poor-ozone air masses from the poles towards midlatitudes) and subsequently to very high levels of solar UVB radiation at the Earth’s surface (Bernhard and Stierle, 2020; Petkov et al, 2014). Over many midlatitude stations of the Northern Hemisphere, changes in aerosols and clouds – and not ozone – have been found to be the main drivers of the long-term changes in the UVB and the UVA irradiance (Chubarova et al, 2020; De Bock et al, 2014; Fitzka et al, 2012; Fountoulakis et al, 2016, 2018; Hooke et al, 2017; Lin et al, 2017; Zhang et al, 2019).

Data and methodology
Short-term variability of UV irradiance and the role of changes in GPH
Long-term variability in the period 2006–2020
Long-term variability at Rome for the period 1996–2020
Findings
Summary and conclusions
Full Text
Paper version not known

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call