North-Atlantic surface winds examined as the source of winter warming in Europe

Trajectories traced backward from western Europe point to the warm southwestern North Atlantic as the source region of the warm maritime air brought into Europe by low‐level southwesterlies. Over the eastern North Atlantic, patterns of ocean‐surface winds in late winter changed during the second half of the 20th century, and the southwesterly direction became even more predominant. In January‐to‐March, the strength of southwesterlies in this region and in source region increased significantly in the years 1948–1995, and is likely to account for a large part of the observed warming in Europe during this period. For 1996–2001, however, this trend in southwesterlies appears broken, consistent with a downturn of the winter warming reported from central Europe after 1995. Monthly indexes of North Atlantic Oscillation, NAO, show a similar pattern, rising till 1995 and a downturn for the 1996–2002 winters and early spring, indicating that this climate oscillation is associated with the NAO.