Quantifying the respective roles of aerosols and clouds in the strong brightening since the early 2000s over the Iberian Peninsula

Abstract

The contribution of clouds and aerosols to the decadal variations of downward surface shortwave radiation (SSR) is a current controversial topic. This study proposes a method, which is based on surface-based SSR measurements, aerosol observations, and radiative transfer simulations (in cloud-free and cloud-and aerosol-free scenarios), to evaluate cloud-aerosol (CARE), cloud (CRE), and aerosol (ARE) radiative effects. This method is applied to quantify the role played by, separately, clouds and aerosols on the intense brightening of the SSR observed in the Iberian Peninsula. Clouds and Earth's Radiation Energy Budget System (CERES) and surface-based data exhibit an increase in SSR between 2003 and 2012, exceeding +10 W m À2 over this period for some areas of the peninsula. The calculations are performed for three surface-based sites: Barcelona and Valladolid (Spain), and Évora (Portugal). Ranges in monthly values of CARE, CRE, and ARE are (À80, À20), (À60, À20), and (À30, 0), respectively (in W m À2 ). The average trends for the analyzed period of CARE, CRE, and ARE are +7, +5, and +2 W m À2 per decade, respectively. Overall, three fourths of the SSR trend is explained by clouds, while the other one fourth is related to aerosol changes. The SSR trends explained by the clouds and aerosol radiative effects are in line with the observed reductions in total cloud cover and aerosol load (both at the surface and in the whole atmospheric column). Furthermore, the CRE values are compared against CERES data showing good agreement between both data series, although some discrepancies are observed in their trends.

Aerosol radiative effects in the ultraviolet, visible, and near-infrared spectral ranges using long-term aerosol data series over the Iberian Peninsula

“…As was reported by Aas et al (2013), the particulate matter (PM) emissions in the Iberian Peninsula have decreased around 25 % between 2000 and 2011. Furthermore, observational PM data in different Spanish sites have also shown a decreasing trend in the 2000s (e.g., Barmpadimos et al, 2012;Cusack et al, 2012;Pey et al, 2013;Bennouna et al, 2014;Mateos et al, 2014). This fact can be understood by the effect of the current economic crisis and the implementation of new environmental laws to control the pollution (e.g., Querol et al, 2014).…”

Validation of CM SAF Surface Solar Radiation Datasets over Finland and Sweden

“…They found that cloudiness decrease appears to be the main driver for the 1990s-2000s brightening in Scandinavia, with likely additional contributions from decreasing aerosol concentrations. The relative contributions of cloud and aerosol effects may vary between Northern and Central Europe, although a strong cloudiness influence on SSR trends has also been found for the Iberian Peninsula [49]. Attribution of the differences in SSR trends and their drivers is a goal for future research, and one where satellite-based datasets such as CLARA and SARAH can play substantial roles.…”

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

“…In the context of Europe there have been a considerable number of regional studies that focus on trends in global radiation and their attribution, such as in Germany (Liepert and Tegen, 2002;Liepert and Kukla, 1997;, in Germany and Switzerland combined (Ruckstuhl et al, 2008;Ruckstuhl and Norris, 2009;Ruckstuhl et al, 2010), in Estonia (Russak, 2009), in the general Baltic states (Ohvril et al, 2009), in Spain (Mateos et al, 2014), in Norway (Parding et al, 2014), northern Europe in general (Stjern et al, 2009) and in Italy (Manara et al, 2015). Even though there are regional differences, the summarized global or allsky radiation data from Europe combined display a minimum in [1984][1985] at the end of a "dimming" period with a subsequent return to higher values.…”