Implications of enhanced persistence of atmospheric circulation for the occurrence and severity of temperature extremes

The relationship between persistent atmospheric circulation patterns over Europe and surface air temperature anomalies is studied for the 20th century using the Hess-Brezowsky catalogue of circulation types and temperature data from Prague. Circulation types significantly conducive to heat and cold waves are detected. It is demonstrated that the persistence of the circulation patterns is linked to surface air temperature anomalies and the occurrence and severity of temperature extremes that become more pronounced under more persistent circulation. The consequences vary for warm and cold extremes, depending on features related to atmospheric dynamics (e.g. air-mass advection and fronts). The intensification of anomalies due to higher persistence of circulation patterns would likely be more important for warm temperature extremes than the cold ones. The recently observed increases in the frequency and severity of heat waves over Europe are likely related to enhanced persistence of the atmospheric circulation, and the impacts of the expected climate change on the occurrence and severity of temperature extremes may be exacerbated by more persistent circulation patterns over the European midlatitudes. Copyright (c) 2007 Royal Meteorological Society.