Warm and cold monthly anomalies across the Mediterranean basin and their relationship with circulation; 1860-1990

Anomalously warm and cold months in the Mediterranean basin were identified during the period 1860–1990 from observations at five stations located along the west–east axis of the Mediterranean basin (Barcelona, Florence, Malta, Athens and Jerusalem), supplemented by data from Madrid and Lisbon. Warm months were characterized by thermic indices (TI) based on values of the standardized anomalous temperatures. Different patterns of anomalously warm and cold months were qualitatively identified on the basis of the spatial distributions of the TIs. The standardized sea-level pressure (SLP) values at 56 grid points in the domain 35–65°N, 30°W–40°E, for each of the anomalously warm and cold months, were subjected to T-mode Principal Component Analysis. The mean TIs associated with each principal component in each season, for both warm and cold months, are arranged in four distinct different spatial distributions: (i) a Mediterranean-wide distribution of positive/negative anomalies; (ii) strong positive/negative anomalies in the west and central Mediterranean and weaker anomalies in the east; (iii) strong positive/negative anomalies in the eastern Mediterranean and weaker anomalies in central and western parts; (iv) strong positive/negative anomalies in the central Mediterranean and weaker anomalies in eastern and western parts. Finally, monthly mean charts of standardized anomaly and mean sea-level pressure charts are constructed for each principal component in each season, and are used to interpret the spatial distribution of the positive and negative temperature anomalies in terms of mean circulation over the domain.