Conte, M. (Istituto di Fisica dell'Atmosfera, CNR - Roma Italy)
Colacino, M. (same affiliation)
Piervitali, E. (same affiliation)
An analysis is performed of the yearly precipitations in the western and central sector of the Mediterranean area in the period 1951-1995. The area is divided in three belts: northern belt (42N-46N), central belt (38N-42N) and southern belt (34N-38N). In each belt about 20 stations are contained and their influences are weighted using the THIESSEN technique (1964). Adopting the method of the absolute amount, of the Standardised Anomaly Index and of the percentiles a significant decrease is pointed out in all the belts. This decrease seems to be correlated with the Mediterranean Oscillation, that is an oscillating growth of the anticyclonic persistence in the western-central Mediterranean basin, firstly determined by CONTE (1992) and them examined also by DOUGUEDROIT (1994) and by CORTE REAL (1995). In addition the percentage decrease of the rainfall is significantly (test of LEPAGE) higher in the southern belt, outlining this fact a northern displacement of desertification in agreement with the wellknown mechanism developed by CHARNEY (1975). A seasonal analysis points out that the observed decrease is mainly concentrated in the cold season.In the area delimited by the western coasts of Italian peninsula, Corsica, Sardinia, Sicily, Tunisia and Malta, which is the core of the Mediterranean climate as defined by KOEPPEN (1936), this type of climate undergoes oscillations both south- north and west-east. This phenomena was also noted by FARMER (1993) and by PALUTIKOF (1996).
Also a brief analysis of extreme mesoscale events is carried out and atentative for revealing their causes in the atmospheric Mediterranean circulation is performed.