SPATIAL AND TEMPORAL FLUCTUATIONS OF MONTHLY RAIDFALL IN THE BRITISH ISLES AND VARIATIONS IN THE MID‐LATITUDE WESTERLY CIRCULATION

Abstract

The spatial pattern of monthly and seasonal rainfall fluctuations over the British Isles between 1942–1970and 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 ereas, whereas increases between April and July occur generally in eastern disricts. This is a consequence of an enhanced seasonal cycle in the vigour of mid-latitude westerly circulation. An increased proportion of annual rainfall in the winter halfyear 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 changes.