Recent drought in California and western Europe

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Abstract
This paper relates the California and west European droughts of 1976 to contemporary and antecedent atmospheric and oceanographic factors. An observed anomalous warming of 3°–4°C from the surface to 10 km in the core of these droughts and diminishing relative humidities in the lower troposphere can be accounted for by subsidence of the order of several hundred meters per day. During winter, extremely strong high‐latitude westerlies and strong subtropical highs extended into western areas of the United States and west Europe. The hemispheric wave number increased from four in the winter of 1976 to five in the summer, the new troughs being formed in areas where lower‐boundary temperature contrasts existed. Newly derived seasonal teleconnections suggest that anomalous ageostrophic banking to the right of the high‐latitude westerlies, reinforced by sea surface temperature (SST) gradients, created the anomalous winter subtropical anticyclones. The summer drought‐producing circulation over west Europe, according to statistically derived teleconnections, was highly compatible with numerous remote anomalies but was probably forced largely by overlying and distant atmospheric responses to the strong central Atlantic SST gradient. Interannual lag correlations between sea level pressure patterns, as well as SST patterns, were unusually high between the winters and between the summers of 1975 and 1976 and appear to have increased over the past 5 years. It is theorized that these runs of recurrent circulations are due to atmosphere‐ocean coupling wherein subsurface anomalously warm or cold water, generated in the cold seasons over a deep mixed layer, has a tendency to be brought to the surface whenever wind stirring is enhanced. This usually occurs in the subsequent fall and winter.