A hybrid method for reconstructing the historical evolution of aerosol optical depth from sunshine duration measurements

Abstract

Abstract. A novel method has been developed to estimate aerosol optical depth (AOD) from sunshine duration (SD) measurements under cloud-free conditions. It is a physically based method serving for the reconstruction of the historical evolution of AOD during the last century. In addition to sunshine duration data, it requires daily water vapor and ozone products as inputs taken from the ECMWF 20th century reanalysis ERA-20C, available at the global scale over the period 1900–2010. Surface synoptic cloud observations are used to identify cloud-free days. For 16 sites over Europe, the accuracy of the estimated daily AOD, and its seasonal variability, is similar to or better than those from two earlier methods when compared to AErosol RObotic NETwork measurements. In addition, it also improves the detection of the signal from massive aerosol events such as important volcanic eruptions (e.g., Arenal and Fernandina Island in 1968, El Chichón in 1982 and Pinatubo in 1992). Finally, the reconstructed AOD time series are in good agreement with the dimming/brightening phenomenon and also provide preliminary evidence of the early-brightening phenomenon.

Reconstruction of daily global solar radiation under all‐sky and cloud‐free conditions in Badajoz (Spain) since 1929

“…Further research is needed in this area including more stations from other regions of Europe in order to smooth the noise and to extract only the physical signal. Overall, our results also emphasize the potential of GHI and cloud cover data to achieve information of the aerosol load in the atmosphere (Sanchez‐Romero et al, 2014; Wandji Nyamsi et al, 2020). This is a vital issue due to the lack of reliable information about its variation before the satellite era.…”

Evidence for Clear‐Sky Dimming and Brightening in Central Europe

“…The SSR variations therefore have to be due to changes within the climate system, namely in the transparency of the atmosphere for solar radiation. It has been argued that variations in aerosol loadings due to varying air pollution may have caused these variations, since the transition from dimming to brightening temporally coincided with changes in air pollution levels and associated changes in aerosol emission and optical depth (Kudo et al., 2012; Nyamsi et al., 2020; Ruckstuhl & Norris, 2009; Streets et al., 2006; Turnock et al., 2015; Wang et al., 2012; Wild et al., 2005). Similarly to the SSR, these emissions also show a distinct trend reversal during the 1980s particularly in industrialized countries, associated with the implementation of air pollution regulations and the breakdown of the former Soviet Union (e.g., Stern, 2006; Streets et al., 2006; Wild, 2009).…”

Opinion: The strength of long-term comprehensive observations to meet multiple grand challenges at different environments and in the atmosphere

“…Sporre et al, 2020). In the temporal and spatial scales of ESMs even the observational record as a whole remains brief and irregular, and therefore the observations must be extended by proxies of changes in the historical period (Wandji Nyamsi et al, 2020) and towards the Earth's deep past over millions of years (Wong et al, 2021). Only integrated long-term observations can provide multidisciplinary data to support evaluation of simulated Earth system feedbacks and their components.…”