Euro-Atlantic blocking events and their impact on surface air temperature and precipitation over the European region in the 20th century

摘要

ABSTRACT: An assessment of blocking events over the Euro-Atlantic domain and their impact on surface air temperature and precipitation variability during the cold season is presented using the most long-term atmospheric circulation reanalysis (20th Century Reanalysis). Blocking situations were defined using the standard blocking index, which is based on the difference of 500 hPa geopotential heights. We discuss the Euro-Atlantic blocking links to large-scale circulation. Blocking index analysis confirms the existence of decadal and multidecadal fluctuations. Results also show that the number of blocking days increased up to 50% in mid-January and in the second part of February. Most cases of anomalous cold and dry weather in northern Europe correspond to blocking processes settled west of 30°W in the North Atlantic, while significant negative air temperature anomalies in southeastern Europe/Black Sea region develop when the blocking high settles east of 10°W. Blocking flow also redistributes the typical precipitation patterns over Europe. A large part of Europe experiences a precipitation increase when the blocked longitudes range between 70° and 30°W. However, further displacement of the blocks to the east results in prevailing dry conditions over Europe, except for the Mediterranean region, the Scandinavian mountains, and Iceland, where precipitation stays above normal.