Atmospheric circulation characteristics favoring wet season prolonged spatially extended dry spells in Greece

Houssos E. E., Fotiadi A. and Lolis C. J. (2016)
In the proceedings of the 13th International Conference on Meteorology, Climatology and Atmospheric Physics, Thessaloniki, Greece, September 2016


The Mediterranean area is a climate sensitive region particularly vulnerable to present and future climate variability, facing a growing threat of drought. In this study, both spatially and temporally extended Dry Spells (DSs) for the wet season (November-March) are identified, based on daily precipitation data from 15 stations spread over the Greek area, along an extended period from 1959 to 2002. Then, 81 Prolonged DSs (PDSs) are found, having duration equal or longer than 5 days, which corresponds to the 90th percentile of the DSs duration’s distribution. The PDSs have a mean and maximum duration of 7 and 18 days respectively. With the synergistic use of Factor and Cluster Analysis, applied on mean sea level pressure and 500 hPa geopotential height daily patterns, the main characteristics of the atmospheric circulation evolution before, during and after these spatially extended PDSs are revealed and examined. The results show that the PDSs are related to the gradual establishment of abnormal anticyclonic circulation over Southern Europe and the Mediterranean Basin.