Summer daily precipitation variability over the East Anglian region of Great Britain

Daily precipitation totals for live Consecutive summers (1994-1998) were obtained for 136 stations ill East Anglia to explore geographic variations ill rainfall. S-Mode principal components analysis (PCA) was used to identify the main spatial modes of variability in the region's precipitation field. The components were interpreted physically by examining synoptic charts and the British Isles' circulation variables for the days with high PC scores. Whilst seven principal components have eigenvalues greater than 1, and collectively explain 86.3% of the variance. only the first 5 PCs have well defined rainfall patterns that call be attributed to specific circulation patterns. The most dominant pattern (PC 1) shows a gradient between wetter conditions in NE Norfolk and drier conditions in Cambridgeshire and Essex, which is favoured by a cyclonic northerly airflow. PC 2 is almost as dominant, and shows a west to east decay ill rainfall totals that is typically associatecd with active zonal W-SW flows. PC 3 sees the highest totals occurring ill Essex. Wetter conditions ill the South of East Anglia tend to occur when areas of low pressure follow a southerly track along the English Channel and southern North Sea. PC 4 shows a maximum in convective activity that occurs furthest inland in SE Cambridgeshire and west Suffolk, with the convection being triggered or accentuated by the East Anglian Heights (the highest land ill East Anglia). PC 5 shows the rainfall distribution under a cyclonic N-NW. whereby showers generated over The Wash penetrate inland and produce the most rainfall in west Norfolk. Finally, a summer precipitation regionalization was derived by applying agglomerative hierarchical cluster analysis to the loading,, of PCs 1-7. It is Concluded that a location's precipitation climatology is more strongly determined by the orientation of the nearest coastline rather than simply the site's distance from the North Sea. Copyright (C) 2008 Royal Meteorological Society