Atmospheric Circulation Changes Associated with the Warming over the Northern North Atlantic in the 1920s

Abstract

A sharp increase in the Arctic mean winter temperature occurred around 1920. The occurrence of consistently positive temperature anomalies at Spitsbergen (starting in 1919), Iceland (1921) and Greenland (1926) subjoined the more gradual warming trend over northern Europe which had been in progress since the mid-1890s. The atmospheric circulation changes associated with the warming of the 1920s are examined using the historical surface weather maps, surface zonal and meridional wind components and station air temperature data. From 1900 to 1925, when European winters were gradually becoming milder, winters in Greenland were generally colder than the 1851–1960 normal. The mean Icelandic Low reached maximum intensity and a northernmost position at about 65°N latitude throughout the period. After 1925, the Low shifted closer to the southern tip of Greenland; this was accompanied by a slight weakening of the westerlies and an increase in meridional flow (southerly) over Greenland and Baffin Bay. In northern Europe the westerlies maintained their pre-1926 strength. In the warmest winters of 1926–44, the westerlies advected mild air over Europe while southerly air flow prevailed over Greenland. In some winters, however, the European westerlies weakened and only Greenland was mild. After 1944, the mean position of the Icelandic Low shifted eastward and the warm period over the Atlantic arctic sector ended.