A classification of deep cyclones over Poland (1971–2000)

The paper proposes a classification of deep cyclones determining the weather in Poland grouped according to their track. The study used data from NCEP/NCAR reanalysis spanning the period 1971–2000. The analysis considered: values of 1000 hPa geopotential height at 12 UTC recorded at selected grid points, maps of 1000 and 500 hPa geopotential height and maps of sea-level air-pressure field at 12 UTC.Seven groups of deep cyclones were identified. The dominant groups involved cyclones originating over the North Atlantic and crossing over Iceland (T2 = 29.3%), and those moving from west to east, typically over the British Isles (T3 = 26.8%). Other large groups of cyclones involved systems travelling from the Mediterranean towards north-eastern Europe (T7 = 10.5%), and those moving from the Norwegian Sea though the Baltic Sea into northern and north-eastern Europe (T1 = 8.4%).Cyclones, with air pressure ranging from 940 to 1000 hPa, were found to have different levels of influence depending on the region. Most of the systems were recorded between October and March (86.4%), but isolated cases were also observed in summer. No statistically significant long-term trends in their occurrence were identified.