Sunshine and synoptic cloud observations at Ebro observatory, 1910-2006

The aim of this study is to characterize the evolution of the number of bright sunshine hours and cloudiness at Ebro Observatory. Sunshine and synoptic cloud observations, extending over almost a century, are available from the Ebro Observatory in the north-east of Spain. Here, we analyse these time series and find a strong decadal variability in the duration of bright sunshine hours since 1910, but without a statistically significant long-term trend. A comparison with sunshine records from other Spanish Mediterranean observatories was also performed to validate the Ebro time series over the shorter time interval for which comparison stations are available. At the same time, we find a monotonic increase in synoptic cloud amount since the 1920s. Time series of cloudiness at different heights are also available at Ebro in digital form dating from 1954, and their analysis allows us to interpret these results as a change in cloud type frequency, possibly coupled with changes in air transparency.