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.
Highlights
Aerosols in the atmosphere are generally produced by natural and anthropogenic mechanisms, e.g., dust and sea salt triggered by wind-driven processes or carbonaceous aerosols from combustion in urban/industrial processes or from biomass burning
We have proposed a new method for estimating aerosol optical depth (AOD) from sunshine duration measurements
The method is used for reconstructing the historical AOD under cloud-free conditions as far back into the past as possible using in addition to the sunshine duration measurements daily total ozone column and total water vapor from the European Centre for MediumRange Weather Forecasts (ECMWF) 20th century reanalysis ERA-20C, which are available at the global scale from 1900 to 2010
Summary
Aerosols in the atmosphere are generally produced by natural and anthropogenic mechanisms, e.g., dust and sea salt triggered by wind-driven processes or carbonaceous aerosols (organic and black carbon) from combustion in urban/industrial processes or from biomass burning. They play a crucial role in the Earth’s climate through their direct effects by scattering and absorbing solar radiation (Charlson et al, 1992; Hansen et al, 1997) and their indirect effects by acting as cloud condensation nuclei (Tang et al, 2016). A significant source in this uncertainty is linked to the limited knowledge of the historical evolution of aerosol load. It has become of great importance to the scientific community to estimate the historical evolution of aerosol load accurately
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