Reconstructing sunshine duration and solar radiation long-term evolution for Italy: a challenge for quality control and homogenization procedures

In the last two decades, the scientific community has become aware of the fact that the real climate signal in original series of meteorological data is generally hidden behind non-climatic noise caused by a number of factors. Time series of meteorological data can therefore not be used for climate research without facing this issue. In this context, we have recently set up a database of Italian sunshine duration and solar radiation daily records and we have subjected them to a detailed quality check and homogenization procedure. Moreover, as the records are rather sparse and a significant fraction of them have wide gaps, we completed the data and set up a procedure in order to obtain at first a gridded version of the dataset and then average records that are representative of the entire Italian territory. The paper will highlight the main steps of the methodology that allowed us to get these average quality-checked and homogenized records and will discuss some open issues.