Circulation dynamics of mediterranean precipitation variability 1948-98

摘要

Canonical correlation analysis is used to identify main coupled circulation-rainfall patterns and to relate recent variability and trends of Mediterranean precipitation to large-scale circulation dynamics. Analyses are based on geopotential heights (500 and 1000 hPa levels) for the North Atlantic-European area (National Centers for Environmental Prediction-National Center for Atmospheric Research reanalysis) and on highly resolved (0.5°* 0.5°) monthly rainfall grids (Climatic Research Unit, Norwich) selected for the Mediterranean area during the 1948-98 period. Combining monthly analyses with similar characteristics to seasonal samples yields winter (October-March), spring (April-May) and summer (June-September) types of coupled variability; a particular autumn type for the whole Mediterranean does not occur on the monthly time scale. Coupled patterns specifically linked to one or two seasons include an east Atlantic jet (EA-Jet) related pattern for summer and a Mediterranean meridional circulation (MMC) pattern for winter and spring. The most important pattern recurring with dynamical adjustments throughout the whole year reflects the seasonal cycle of the Mediterranean oscillation (MO), which is linked (with seasonal dependence) to the Northern Hemisphere teleconnection modes of the Arctic oscillation (AO) and North Atlantic oscillation (NAO). Winter rainfall trends of the recent decades marked by widespread decreases in the Mediterranean area and by opposite conditions in the southeastern part are linked to particular changes over time in several of the associated circulation patterns. Thus, different regional rainfall changes are integrated into an overall interrelation between Mediterranean rainfall patterns and large-scale atmospheric circulation dynamics.