THE GREAT PACIFIC ANTICYCLONE OF WINTER 1949–50: A CASE STUDY IN THE EVOLUTION OF CLIMATIC ANOMALIES

Abstract

The sea-level and 700-mb circulations over the North Pacific and United States from December 1949 to March 1950 are studied with the help of daily charts and means for five-, fifteen- and thirty-day periods. As the period of averaging increases, the apparent chaos of the daily maps gradually dissolves and a remarkably regular evolution emerges as a vast warm anticyclone moves in a great arc from the southeast Pacific into the Bering Sea and Canadian Yukon. The influence of this mean anticyclone on Pacific storm tracks and anomalies over the United States is described. Although a satisfactory explanation of the amazingly long life of the cell is not offered, some relevant physical facts are presented; they indicate the importance of the temperature of the underlying surface and large-scale mixing with the environment. Finally, a hypothesis is suggested to account for the motion of the great anticyclone and possibly to explain the variations in atmospheric circulation which give rise to climatic anomalies of long duration.