Atmospheric blocking is a large-scale mid-latitude circulation phenomenon characterized by a persistent anticyclone that interrupts the typically westerly flow. Atmospheric blocking can cause extreme near surface temperature conditions either by the advection of anomalously cold or warm air in the outer region of the block or by anomalies in the surface radiative budget in the center of the block. Summertime blocking conditions were closely linked to the 2003 European heat wave centered in France and the 2010 Western Russia heat wave.
This talk will address the linkage between blocked flow and warm spells over Europe by utilizing a suite of CCSM4 simulations. Summertime blocking over Europe and related climate conditions are realistically represented in this climate model. The analysis of observations and a multi-century Year 2000 simulation suggests that summertime warm spells in Scandinavia and Western Russia are closely controlled by blocking while mid-latitude temperature extremes in Western Europe are less sensitive to this circulation phenomenon. This talk closes with a discussion on the potential role of climate change on the linkage between blocking and temperature extremes.