Autumn and Extended Winter Daily Precipitation Variability over Central and Southern Scotland

Abstract

This paper analyses the main geographic patterns of rainfall variability over Central and Southern Scotland at the daily timescale during the autumn and extended winter (SONDJFM) period. Principal component analysis (PCA) is used to identify the most important rainfall patterns, with the first eight principal components (PC) accounting for 85.2% of the variance. The most important pattern (PC 1) is associated with a cyclonic W/SW flow and produces the wettest conditions in Renfrewshire and Dumbartonshire (PC 1); rainfall under the PC 1 pattern is widespread, with even the drier sites in eastern Scotland recording comparatively high totals. PC 2 produces wetter than average conditions in eastern Scotland (especially the Scottish Borders region) and so reduces the average rainfall gradient between the west (wetter) and the east (drier). All eight significant PCs are explained in terms of the atmospheric circulation and the geography of Scotland. Cluster analysis is then used to identify coherent rainfall regions. The regions on easterly days show the most difference from the other directions and the regions derived across all days.

Key Words:

• rainfall
• autumn
• winter
• principal component analysis
• cluster analysis
• atmospheric circulation

Acknowledgements

The authors would like to thank Mrs Anne Ankcorn of the Drawing Office, School of Geography, Earth and Environmental Sciences, University of Birmingham for drawing all of the figures. The British Atmospheric Data Centre (BADC) is acknowledged as the source of the rainfall data. Kieran Smith would like to thank Max Fisher and Tracy Crago. The comments of the three reviewers are also acknowledged. This paper is a summary of the first author's MSc Meteorology and Climatology dissertation.