SEASONAL INTERACTIONS BETWEEN THE NORTH PACIFIC OCEAN AND THE ATMOSPHERE DURING THE 1960's

Abstract

An attempt is made to explain the large-scale seasonal ocean-atmosphere interactions that occurred from 1961 through the winter of 1967–68 and that led to a special “climatic regime” over the North Pacific and North America. This regime was characterized by anomalously warm water over the central ocean, which helped generate atmospheric circulations of a kind favoring the persistence of the warm water, especially in the nonsummer seasons. The prevailing atmospheric circulation generated by the warm water during winter consisted of strong and southward-displaced cyclogenesis that produced a standing (Rossby) long wave downstream, resulting in climatic cooling over the eastern two-thirds of the United States. A theory is advanced for the evolution of atmospheric pressure and sea-surface temperature patterns in other seasons based on theoretical and empirical considerations. The inception of the regime came abruptly in the late summer and fall of 1961, following several years when the eastern North Pacific Ocean slowly cooled over a vast area and to great depths. This cold pool of water appears to have been responsible for strong development of the Pacific High in the fall of 1961, probably through reducing the depth and outflow in the friction layer. The strong anticyclogenesis then set up numerous processes (particularly anomalous Ekman drifts and heat exchanges), the net result of which was to replace anomalously cold surface water with warm water, especially in the central North Pacific. The newly established thermal regime in the upper layers of the sea became dominant and seemingly irreversible for several years. If these ideas carry a germ of the truth, one should expect spells of abnormality lasting several years in both atmosphere and sea and abrupt transitions between spells.