Climatic reversal in northern North Atlantic

Abstract

OVER the European arctic and subarctic seas the atmospheric circulation has recently tended towards northerly airflow, with an accompanying climatic deterioration. Since the 1950s direct northerly outbreaks have swept the Norwegian–Greenland Sea with increasing frequency, adding almost every year, particularly in the 1960s, to the severity of the climate in areas as far south as the British Isles. This change has been associated with the establishment over Greenland in the early 1950s of a persistent ridge of pressure anomaly and with its subsequent maintenance and intensification (on average) throughout the Jate 1950s and 1960s. Compared with the ‘normal’ climatic period of 1900–39 this cell represented an increase of over 3 mbar in the mean annual pressure at sea level in Greenland over the period 1956–65, but was very much more pronounced during the cold season (November–March). During the winter quarter (December–February), the increase in the mean pressure at sea level in Greenland amounted to over 7 mbar between 1900–39 and 1956–65 (Fig. 1a) and the pressure rise continued during the late 1960s. (Throughout, listed dates refer to the second year of the winter in question; thus, “winter 1956” refers to the period December 1955–February 1956.) A further increase of over 5 mbar occurred in Greenland between the winters of 1956–65 and 1966–70 (Fig. 1b). Coupled with a slight decrease of pressure over the eastern Norwegian and Barents Seas this change has resulted in “… a remarkable difference of pressure between Greenland and the eastern Norwegian Sea; this has increased since 1950 in every month of the year …”¹.