Cloudiness climatology in the Iberian Peninsula from three global gridded datasets (ISCCP, CRU TS 2.1, ERA-40)

A climatic description of total cloudiness in the Iberian Peninsula is presented, based on three global gridded datasets: the International Satellite Cloud Climatology Project (ISCCP) D2 data, gridded data (TS 2.1) from the Climate Research Unit (CRU), and the ECMWF Re-Analyses data (ERA-40). While the first grid data product is based on satellite imagery, the second series is from observations from the surface, and the third uses several types of observations that are assimilated into a grid. Since the series differ in their extension, the study has been limited to the shared period of 1984-2002 in regards to comparing results from the three sources of data. These results indicate that, in the Iberian Peninsula, the mean annual cloudiness ranges from 35-65% of fractional sky cover, depending on location and on data source. Seasonal evolution shows a very clear minimum of cloudiness that appears in summer and a maximum in winter. Important differences appear among the three sources; these differences are variable both in space and during the year. Regarding decadal trends of cloudiness, the results are sometimes contradictory: on an annual basis, ISCCP and ERA indicate general decreasing cloudiness, while CRU data show a continuous positive trend.