Spatial and temporal fluctuations of monthly rainfall in the British Isles and variations in the mid-latitude westerly circulation

The spatial pattern of monthly and seasonal rainfall fluctuations over the British Isles between 1941-1970 and 1961-1990 are interpreted in the context of changes in atmospheric circulation. Increases in rainfall in autumn, winter and early spring occur largely in north-western areas, whereas increases between April and June occur generally in eastern districts. This is a consequence of an enhanced seasonal cycle in the vigour of the mid-latitude westerly circulation. An increased proportion of annual rainfall in the winter half-year and an associated decrease in the contribution of summer (June, July and August) rainfall are consistent with changes in the seasonal distribution of rainfall and associated forcing factors suggested by coupled ocean-atmosphere models of future climatic change.