Reconstruction of long‐term aerosol optical depth series with sunshine duration records

Abstract

We report the suitability of sunshine duration (SD) records as a proxy for the reconstruction of atmospheric aerosol content, for which little information exists, especially prior to the 1980s. Specifically, we have treated cloudless summer days in 16 stations throughout Spain. For almost all sites we find statistically significant relationships between aerosol optical depth (AOD) and daily SD. The correlation coefficient presents a mean value of −0.72, and slope values of the linear regressions are within the range [−0.11, −0.36]. The relationships are used to generate AOD series back to the 1960s (to the 1920s for Madrid). These reconstructed series show an increase in AOD from the mid‐1960s to the 1980s, followed by a decrease until the present, in agreement with changes in anthropogenic aerosol emissions and with opposite trends of solar irradiance. The method can be used to reconstruct AOD from the late nineteenth century at many stations worldwide.

Detection of dimming/brightening in Italy from homogenized all-sky and clear-sky surface solar radiation records and underlying causes (1959–2013)

“…This suggested that during the global dimming/brightening periods there is an important fraction of SD evolution that cannot be explained by cloud cover changes which must therefore depend on other factors such as changes in aerosol optical thickness. The temporal variations in aerosol optical thickness of the last decades seem to be mainly driven by anthropogenic emissions (Streets et al, 2006(Streets et al, , 2009, even though, especially for southern Italy, mineral particles originating from Sahara and Sahel areas may also have a significant role, as recently suggested for Spain by Sanchez-Romero et al (2016). This natural atmospheric aerosol, with emissions that are highly variable from year to year, is a significant component of the Mediterranean area Varga et al, 2014) causing reflection and absorption of the incoming solar radiation and therefore affecting the energy balance together with anthropogenic aerosols (Zhu et al, 2007).…”

“…Specifically, we represent the length of the period considered for the analysis (y axes) in relation to the starting year of the window that the trend refers to (x axes). Slopes are shown by means of the colors of the corresponding pixels, with large squares for trends with a significance level of p ≤ 0.1 and small squares for trends with a significance level of p > 0.1 (considered here statistically non-significant), with significance levels estimated by means of the Mann-Kendall nonparametric test (Sneyers, 1992).…”

Is the summer season losing potential for solar energy applications in South Africa?

“…The device (sunshine recorder) for measuring sunshine hours is simple (more details in Section 2), but useful information can be generated from the data and can be employed in many areas of research. This data has been used in several studies, including for air quality (Sanchez-Romero et al, 2016;Li et al, 2016); environmental pollution (Kaiser and Qian, 2002;Statheropoulos et al, 1998); energy (Yaiche et al, 2014); and solar radiation prediction modelling studies (Mulaudzi et al, 2015;Adeyemi et al, 2015;Singh et al, 2011). The sunshine hour of any day is affected by varying atmospheric and sky conditions, so SD can, therefore, indirectly indicate atmospheric turbidity, visibility and sky conditions.…”

Nubosidad y radiación solar en la Península Ibérica entre 1950 y 2050. De las evidencias observacionales a las simulaciones climáticas

“…La mayor parte de los resultados que se presentarán en el siguiente apartado provienen de trabajos ya publicados (Sanchez-Lorenzo et al, 2007;2009;2012;Enriquez-Alonso et al, 2015;Sanchez-Romero et al, 2016). En todas estas referencias se detalla el origen de los datos utilizados.…”

“…Ahora bien, las observaciones directas de carga de aerosoles son escasas antes de la época de los satélites o de la generalización de instrumentos como los heliofotómetros, es decir, antes de los años 1990. Por ello el trabajo de Sanchez-Romero et al (2016) abordó la estimación de la carga de aerosoles (específicamente, de su espesor óptico, AOD) a partir de datos de insolación (para días sin nubes), que se correlacionaron con medidas directas mediante instrumentos Cimel de la red AERONET. Extrapolando hacia el pasado las relaciones entre AOD e insolación obtenidas, se obtuvo una estimación de la evolución del AOD medio para España, desde el año 1960 (ver Figura 7).…”