Wet and dry monthly anomalies across the Mediterranean basin and their relationship with circulation, 1860-1990

Anomalously wet and dry months in the Mediterranean basin were identified d uring 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. Wet an d dry months were characterized by hydric indices (KI) based on values of t he standardized precipitation anomalies. Different patterns of anomalously wet and dry months were qualitatively identified on the basis of the spatia l distributions of the hydric indices. The standardized sea level pressure values at 56 grid points in the domain 35 degrees N-65 degrees N, 30 degree s W-40 degrees E, for each of the anomalously wet and dry months, were subj ected to T-mode Principal Component Analysis. The mean hydric indices associated with each principal component in each se ason are arranged in four distinct different spatial distributions for wet months and in three for dry months as following: (a) Mediterranean wide dis tribution of positive/negative anomalies; (b1) Strong positive anomalies to the west, but weaker to eastern Mediterranean; (b2) Strong negative anomal ies to the west, but weaker or normal to the east; (c1) Strong positive ano malies to the west and to the east and weaker ones to the central Mediterra nean; (c2) Negative anomalies to the west and east, but weaker, or normal, or positive to the central Mediterranean; (d) Relatively strong positive an omalies to the east and weaker ones to the western Mediterranean. Finally, monthly mean charts of standardized anomaly and mean sea level pre ssure are presented for each principal component in each season. These char ts are used to interpret the spatial distribution of the positive and negat ive precipitation anomalies in terms of mean circulation over the domain.