Sea-level pressure variability in the Po Plain (1765-2000) from homogenised daily secular records.

A homogenized 236 year daily regional sea-level pressure (SLP) record is constructed for the Po Plain (north Italy) by means of six station records: Bologna, Genoa, Lugano, Milan, Padua and Turin. Station records are subjected to a first homogenization in order to reduce all observations to sea level and to 0°C and to correct the bias introduced by calculating daily means using different sets of observation hours. A second homogenization is performed by means of comparison with other Italian and European series. After homogenization, the root-mean square error of the yearly station records is evaluated within 0.2 hPa after 1880, whereas for the periods 1834-1880 and 1765-1833 it is estimated as between 0.2 and 0.3 hPa and as around 0.4 hPa respectively. Trend analysis is applied to the annual and seasonal regional records and concerns both SLP and its day-to-day variability. The results show that neither the SLP nor its day-to-day variability have an evident trend when considering the entire 1765-2000 period. However, if the series is divided roughly in two parts, then significant trends can be highlighted. The annual and seasonal regional SLP records are also compared with corresponding regional temperature series. The results show that, especially in spring and in summer, temperature and SLP are in good agreement.