Fine scale spatial variations in wet deposition

Results are presented from an experiment designed to investigate the processes that cause small-scale (sub-20 km) variations in wet deposition to upland terrain in the UK. Bulk rain and orographic cloud collections were made at a network of sites of typical separation 1-3 km. Detailed analysis of two frontal rain events that occurred in westerly and southwesterly flows was aided by the use of a computer model of wet deposition. The accuracy of model predictions of inter-site variations of rain amount and ion deposition in rain is supported by the data except in the lee of higher terrain. This suggests that the model realistically simulates most of the important physical processes which cause fine scale spatial variation in wet deposition. The role of the upstream temperature profile in modifying the deposition through its effect on the position and properties of the orographic cloud is considered. Again, the data support the predictions of the model. (C) 2000 Elsevier Science B.V. All rights reserved.