Relationship between large scale atmospheric processes, sea surface temperature patterns and regional basin scale monthly rainfall

Recent developments in climate research have led to development of a number of seasonal climate forecasting systems.Variation in seasonal rainfall over much of Europe has been related to the North Atlantic Oscillation (NAO), which is associated with changes in atmospheric circulation. North Atlantic Oscillation (NAO) index has been defined as the pressure difference between Azores and Iceland; the positive phase of the NAO reflects below-normal pressure across the high latitudes of the North Atlantic and above-normal pressure over the central North Atlantic, the eastern United States and western Europe. In this work monthly rainfalls in some hydrological basin in Tuscany, Italy, expressed in terms of rainfall depth, are compared with simultaneous and previous patterns of large scale circulation, synthetised by the North Atlantic Oscillation (NAO) index, and patterns of sea surface temperature (SST) in central-western Mediterranean, for the period 1951-1991. Some statistical methods are employed, from simple linear correlations to contingency tables. The final aim of the work was to investigate on the possible role of NAO and SST as predictors in a regional seasonal forecasting system.