Characteristics Of Summer Heatwaves Over Europe And Its Links With European Blocking Circulations

Based on daily surface air temperature at 2m and 500-hPa geopotential height fields from NCEP/NCAR reanalysis datasets, a heat wave index over Europe is used in this paper. The spatial characteristics of heat waves over Europe and associated atmospheric circulations are investigated using the K-mean clustering analysis. It is shown that the heat waves over Europe can be classified as six types of spatial patterns:Wes(?) Europe(WE), Russian(RU), Eastern Europe(EE), Scandinavian(SC), North Sea(NS), Iberian(IB). The European heatwave have a decadal variability, The frequency of heatwave events over Europe is found to increase significantly after 1980s, which may be associated with the global warming. The decadal variability of the summer North Atlantic oscillation (SNAO) index is possibly reason to the decadal variability of European heatwave. While the global warming can increase the frequency of European heat waves, the atmospheric internal processes affecting the strength, position and frequency of European heat waves seem to be dominant. Composite of geopotential height anomalies shows that the occurrence region of European heat waves is determined by the position of blocking anticyclone over Europe that is tightly tied to positive quasi-stationary wave train anomalies over Euro-Atlantic region and the phase of NAO. Low latitude-type heat waves are more likely to take place when the SNAO index decreases to a negative value, while the High latitude-type heat wave occurs during the period when the NAO index is in a positive phase. Moreover, it is found that the NAO event precedes the European blocking by 1-5 days, thus suggesting that the phase of NAO can modulate the European heat waves.