Total cloud cover over Italy (1951-2018): variability and trends

A new quality-checked and homogenised dataset of total cloud cover (TCC) series over Italy for the period 1951–2018 is presented and the variability and trends of the obtained regional series are discussed (https://doi.org/10.1016/j.atmosres.2023.106625). The diurnal cycle highlights the important role of convection induced by solar radiation that, as expected, is more relevant at middle and high altitudes and in summer. In parallel, the annual cycle shows a strong minimum in July and a maximum in winter for southern Italy, while it shows a more complex behaviour with strong differences between low and high altitudes in northern Italy. Moreover, the seasonal and annual TCC series are characterised by a significant negative trend over the whole period considered, mainly due to the period 1951–1990. Although small differences can be observed between northern and southern Italy, the two regions show a coherent behaviour both for the long-term trends and for the decadal time-scale variability, suggesting that the causes of variability and trends of the Italian TCC records are more related to large-scale factors rather than to local scale changes. Indeed, the comparison with sea level pressure and 500-hPa geopotential height data highlights that large-scale atmospheric circulation explains a relevant fraction of the signal of the Italian TCC records. In particular, they show an opposite behaviour highlighting the same rate of decrease/increase especially during the 1970s and 1980s, where the most significant decrease/increase in TCC/SLP and 500-hPa geopotential height is concentrated. Moreover, TCC seems more linked to SLP during winter, spring and autumn while TCC seems more linked to 500-hPa geopotential height during summer, therefore, more linked to higher temperatures. Finally, the new TCC dataset shows that the long-term evolution of sunshine duration (https://doi.org/10.1002/2014JD022560) and surface solar radiation (https://doi.org/10.5194/acp-16-11145-2016) in Italy is only partially influenced by changes in TCC: if TCC would not have been changed over the investigated period, probably the rather weak dimming, due to the increase in the aerosol concentrations before about 1980 (https://doi.org/10.1016/j.atmosenv.2019.116861) would have been stronger, whereas the following rather strong brightening would have been weaker determining a more similar strength of the changes in the dimming and the brightening periods.