Connection between the large-scale 500 hPa geopotential height fields and precipitation over Greece during wintertime

The spatial distribution of the winter (December to February) precipitation over Greece was related to the eastern North Atlantic-European scale mid-tropospheric circulation fields by means of empirical orthogonal functions (EOFs) and canonical correlation analysis (CCA). The data used in this study are winter precipitation totals, of 23 stations, equally distributed over Greece, and winter mean 500 hPa geopotential heights (30 to 70 degrees N, 30 degrees W to 50 degrees E) for the period 1958 to 1994. The Greek precipitation data were found to be homogeneous (Alexandersson test). A decrease of winter precipitation over the whole country was found, although significant (Mann-Kendall trend test) only over the northern and eastern parts and in the western mountainous regions. Three CCA patterns represent links that are very reasonable from a physical point of view. It is supposed that stronger westerlies over the eastern North Atlantic and the raising of the 500 hPa geopotential height (and also the sea level pressure) over continental Europe during the last few decades were connected with enhanced atmospheric stabilization and anomalous advection of cold and dry air from northerly directions. This led to the winter dryness over the eastern Mediterranean. The probable mechanisms and processes in the complex atmosphere-ocean system, leading to the regional anomalous climatic conditions, are discussed.