Abstract In this work, we investigated the correlation between the North Atlantic Oscillation (NAO) index and the rainfall trend in Tuscany (Italy) by using a large number of rain gauges for a high-resolution spatial scale study in a region characterized by significant morphological and climatic variability and equipped with an efficient measurement network. The relationship between NAO and rainfall was calculated by the Spearman's correlation coefficient. Our study shows that the correlation between NAO and precipitation has two types of oscillations as functions of the time scale. During the year the correlation is negative in winter and positive in summer, and this is due to global atmospheric circulation, which causes the area to be affected by humid air masses from the Atlantic Ocean during the winter. It is difficult to understand these experimental observations for the summer period because the correlation is influenced by the low rain levels of this area and the results could be easily influenced by other global patterns. Investigating in particular the period from December to March, we observed a variation in the NAO precipitation correlation also over time, with periods characterized by an increase in anti-correlation. The results obtained for Tuscany were contextualized and compared with other areas of Europe and of the Mediterranean basin by applying the same methodology. Spatial analysis showed that the trend of the NAO and rainfall correlation depends on latitude. In northern Europe, the behaviour of the correlation between NAO and rainfall over time is very similar to the temporal trend of NAO itself; instead, in the southern Mediterranean area this correlation has a trend over time that is very similar to the one of the Atlantic Multidecadal Oscillation (AMO) Index. This allowed us to observe a different regulation in the circulation of the humid air masses coming from the Atlantic Ocean, which induced rainfall in the Mediterranean and in northern Europe. The circulation of humid air masses in Northern Europe is linked to the pressure difference between high and low latitudes (represented by the NAO index), whereas in the Mediterranean it is linked to the temperature of the Atlantic Ocean (represented by the AMO index). The areas between high and low latitudes, characterized by a mixed behaviour, are regulated by both pressure difference and ocean temperature. This study has made it possible to investigate a specific area of the Mediterranean and then to extend and contextualize to more geographical locations, highlighting the fact that simple linear regression models can help to investigate the role of global patterns on the local effects.

中文翻译：

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大尺度环流模式与局部尺度效应之间的统计关系：地中海盆地关键区域的 NAO 和降雨状况

摘要 在这项工作中，我们通过使用大量雨量计在具有显着形态特征的地区进行高分辨率空间尺度研究，研究了北大西洋涛动 (NAO) 指数与托斯卡纳（意大利）降雨趋势之间的相关性。和气候变化，并配备了高效的测量网络。NAO与降雨量之间的关系通过Spearman相关系数计算。我们的研究表明，NAO 和降水之间的相关性有两种类型的振荡，作为时间尺度的函数。年内冬季负相关，夏季正相关，这是由于全球大气环流导致该地区在冬季受到来自大西洋的潮湿气团的影响。很难理解夏季的这些实验观测结果，因为相关性受到该地区低雨量的影响，结果很容易受到其他全球模式的影响。特别是调查 12 月至 3 月期间，我们观察到 NAO 降水相关性也随时间发生变化，其特征是反相关性增加。通过应用相同的方法，对托斯卡纳获得的结果进行了背景分析，并与欧洲其他地区和地中海盆地进行了比较。空间分析表明，NAO和降雨相关性的趋势取决于纬度。在北欧，NAO 与降雨量的相关性随时间变化的行为与 NAO 本身的时间趋势非常相似；反而，在地中海南部地区，随着时间的推移，这种相关性的趋势与大西洋多年代际振荡 (AMO) 指数之一非常相似。这使我们能够观察到来自大西洋的潮湿气团循环的不同规律，这导致了地中海和北欧的降雨。北欧潮湿气团的环流与高低纬度之间的压差有关（由 NAO 指数表示），而在地中海，它与大西洋的温度（由 AMO 指数表示）有关。高低纬度之间的区域以混合行为为特征，受压力差和海洋温度的调节。