NORTH PACIFIC CIRCULATION ANOMALIES, EL NINO AND ANOMALOUS WARMTH OVER THE NORTH-AMERICAN CONTINENT IN 1986-1988 - POSSIBLE CAUSES OF THE 1988 NORTH-AMERICAN DROUGHT

The relationships between 300/1000 mbar thickness anomalies over the North Pacific Ocean and thickness anomalies over the adjacent North American continent are investigated on the basis of monthly anomalies for the 34‐month period January 1986 to October 1988. It is found that in 21 out of the 34 months a pattern exists that links negative anomalies over the North Pacific Ocean to positive anomalies over the North American continent. Using teleconnection analysis, it can be shown, that in spring a strong relationship exists between positive anomalies over the western half of the North American continent in mid‐latitudes and negative thickness anomalies over the North Pacific Ocean in mid‐latitudes as well as between positive anomalies over the North Pacific Ocean in tropical and subtropical latitudes. Statistically, the strongest relationships emerged between the thickness gradient departures 20°–30°N over the east‐central Pacific Ocean and positive anomalies over North America. The abnormal warmth over the North American continent in the springs of 1986, 1987, and 1988 may be explained in terms of an intensified circulation across the Pacific Ocean, which resulted in large positive thickness anomalies downstream over the North American continent. The intensification of those anomalies in the spring of 1988 is discussed as a contributing factor to the initiation of the 1988 North American drought. Copyright © 1990 John Wiley & Sons, Ltd