Influence of NAO and clouds on long‐term seasonal variations of surface solar radiation in Europe

Abstract

This study is an analysis of the seasonal all‐sky surface solar radiation variability in Europe during 1970–2000 using surface observations from the Global Energy Balance Archive (GEBA). On the basis of the annual means period 1970–1985, there is a statistically significant decline of −3.0% decade−1 (−3.8 Wm−2 decade−1) followed by a nonsignificant rise of 0.3% decade−1 (0.4 Wm−2 decade−1) during 1985–2000. The behavior of the solar radiation for spring is similar to the annual series and has the strongest increase of 1.6% decade−1 (2.5 Wm−2 decade−1) during 1985–2000. In summer a similar evolution to the annual and spring time series is shown but has a stronger decline of −3.2% decade−1 (−6.8 Wm−2 decade−1) during 1970–1985. A small positive nonsignificant trend is reported for the winter means time series while a statistically significant negative trend of −2.5% decade−1 (−2.1 Wm−2 decade−1) was found in autumn during 1970–2000. By comparing variations in all‐sky solar radiation with changes in cloud cover and NAO, we attribute the winter and autumn trends mainly to the NAO through the modification of mid‐to‐low cloud cover in southern Europe and the spring and summer trends to mid‐to‐low cloud cover in northern Europe. However, because the cloud cover and solar radiation relationship weakens in the low‐frequency variability, it suggests that other effects such as aerosols may also play a role. In addition, aerosols could be interfering with the relationship between solar radiation and NAO, contributing to a strengthening of their correlation in the low‐frequency variability during winter and autumn.

Reconstruction and analysis of erythemal UV radiation time series from Hradec Králové (Czech Republic) over the past 50 years

“…This can be supported by the statistically significant negative correlation coefficients between the 1000 hPa first PCA component and the AO and NAO indices (Table 6). Although the relationship between air pressure systems and shortwave radiation is expressed mostly through the redistribution of clouds (Chiacchio and Wild, 2010), the results presented in this study indicate that low TOC is the dominant factor affecting the incidence of days with EUV 90+ . Low TOC occurs mostly during the NAO positive phase, which leads to stationary planetary waves, stronger zonal winds, and therefore a colder Arctic circumpolar vortex (Orsolini and Limpasuvan, 2001;Schnadt and Dameris, 2003).…”

The Global Energy Balance Archive (GEBA) version 2017: a database for worldwide measured surface energy fluxes

“…2). Chiacchio and Wild (2010) pointed out that the dimming and subsequent brightening at the European GEBA sites is particularly evident in spring and summer. The longest records in GEBA further indicate an increase in downward shortwave radiation in the 1930s and 1940s, which has been termed early brightening (Ohmura, 2006(Ohmura, , 2009Wild, 2009) (see Fig.…”

Impact of aerosols and clouds on decadal trends in all-sky solar radiation over the Netherlands (1966–2015)

“…Furthermore, cloud optical thickness changes can be the result of changes in microphysics or cloud thickness and current observations are not able to separate the two effects. Nevertheless, modelling and observation studies by Romanou et al (2007), Ruckstuhl and Norris (2009), Chiacchio and Wild (2010), , Liepert and Kukla (1997), Long et al (2009) and Augustine and Dutton (2009) suggest a definite but mixed role for clouds impacting the trend in all-sky radiation.…”