USE OF SIMPLE DAILY ATMOSPHERIC CIRCULATION TYPES FOR THE INTERPRETATION OF PRECIPITATION COMPOSITION AT A SITE (ESKDALEMUIR) IN SCOTLAND, 1978-1984

A simple daily weather type of classification for the British Isles (Lamb, 1972, Geophys. Mem. 16) may be used as a convenient method to categorize precipitation composition (excess SO2-4, NO-3, NH-3, NH+4, H+) at a site in southern Scotland. Precipitation associated with four weather types in particular (Westerly: W, Cyclonic: C, Southerly: S, Southwesterly: SW), has a strong influence on the annual mean precipitation-weighted composition. The single most important influence is the 'dilution' effect of precipitation associated with W-types. Trends in composition over the period 1978-1984 appear to be strongly related to the annual amounts of C-type and, especially, W-type precipitation. These links may confound the relationships between emissions and deposition over a restricted region. The pronounced annual cycle in precipitation composition at the station may also be explained, in large part, by the annual meteorological cycle which can, in turn, be characterized by the weather types. The significance of these findings is that there are known, and large, change in the relative annual frequencies of the major weather types on time-scales of decades. This indicates a possible contribution to non-linearity between emissions and depositions on the longer time-scale. © 1990.