Dafis S, Lolis C.J., Houssos E.E. and Bartzokas A., (2015)
International Journal of Climatology, 36(10), 3561-3577
Abstract
The connection between atmospheric circulation over Europe and snowfall in Ioannina, NW Greece, is examined. The study deals with 160 snow events, referring to the 56-year period 1956–2011. For each of the events, the patterns of 500 hPa and 1000 hPa Geopotential Height, 500 hPa and 850 hPa Air Temperature, 1000–500 hPa, 1000–700 hPa and 700–500 hPa thickness are constructed for the European area, whereas static stability K-Index, Relative Humidity at 500 hPa, 700 hPa and 850 hPa levels and finally Relative Vorticity at 500 hPa and 1000 hPa are also used for the SE Mediterranean region, for the previous day (D-1), the starting day (D) and the day following the cessation of snowfall (END). Factor Analysis and Cluster Analysis are applied to the above data sets and the evolutions of the above circulation parameters are classified into 8 clusters. Snowfall in NW Greece is generally associated with a low pressure system over the Ionian Sea combined with an anticyclone over W or NW Europe, causing cold northwesterly flow in the lower troposphere over NW Greece. In the middle troposphere, a deep 500 hPa trough usually extends from W Russia to Italy and the Ionian Sea. The 8 atmospheric circulation structures differ mainly in the exact location and/or the intensity of the depression and/or the anticyclone, in the orientation of the 500hPa trough axis and in the trajectories of the above synoptic systems between D-1 and END days.