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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 16, issue 17 | Copyright
Atmos. Chem. Phys., 16, 11145-11161, 2016
https://doi.org/10.5194/acp-16-11145-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 08 Sep 2016

Research article | 08 Sep 2016

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

Veronica Manara1,2, Michele Brunetti3, Angela Celozzi4, Maurizio Maugeri1,3, Arturo Sanchez-Lorenzo5, and Martin Wild2 Veronica Manara et al.
  • 1Department of Physics, Università degli Studi di Milano, Milan, Italy
  • 2ETH Zurich, Institute for Atmospheric and Climate Science, Zurich, Switzerland
  • 3Institute of Atmospheric Sciences and Climate, ISAC-CNR, Bologna, Italy
  • 4Italian Air Force, COMET Centro Operativo per la Meteorologia, Pratica di Mare (RM), Italy
  • 5Instituto Pirenaico de Ecología, Consejo Superior de Investigaciones Científicas (IPE-CSIC), Zaragoza, Spain

Abstract. A dataset of 54 daily Italian downward surface solar radiation (SSR) records has been set up collecting data for the 1959–2013 period. Special emphasis is given to the quality control and the homogenization of the records in order to ensure the reliability of the resulting trends. This step has been shown as necessary due to the large differences obtained between the raw and homogenized dataset, especially during the first decades of the study period. In addition, SSR series under clear-sky conditions were obtained considering only the cloudless days from corresponding ground-based cloudiness observations. Subsequently, records were interpolated onto a regular grid and clustered into two regions, northern and southern Italy, which were averaged in order to get all-sky and clear-sky regional SSR records. Their temporal evolution is presented, and possible reasons for differences between all-sky and clear-sky conditions and between the two regions are discussed in order to determine to what extent SSR variability depends on aerosols or clouds. Specifically, the all-sky SSR records show a decrease until the mid-1980s (dimming period), and a following increase until the end of the series (brightening period) even though strength and persistence of tendencies are not the same in all seasons. Clear-sky records present stronger tendencies than all-sky records during the dimming period in all seasons and during the brightening period in winter and autumn. This suggests that, under all-sky conditions, the variations caused by the increase/decrease in the aerosol content have been partially masked by cloud cover variations, especially during the dimming period. Under clear sky the observed dimming is stronger in the south than in the north. This peculiarity could be a consequence of a significant contribution of mineral dust variations to the SSR variability.

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This paper presents the temporal evolution of solar radiation over Italy for the 1959–2013 period and discusses possible reasons for differences between all-sky and clear-sky conditions in order to understand which part of the solar radiation variability depends on aerosols or clouds. The results give evidence of a relevant influence of both anthropogenic and natural aerosols on solar radiation long-term variability.
This paper presents the temporal evolution of solar radiation over Italy for the 1959–2013...
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