Relationships of precipitation chemistry, atmospheric circulation, and elevation at two sites on the Colorado front range

The acidity and conductivity of precipitation at two sites located east of the Continental Divide in the Front Range of Colorado is examined for tempo ral trends, differences, and relationships to atmospheric circulation patte rns for a 14 yr period (1984-1997). The elevationally lower station, Sugarl oaf, is about 20 km west of Boulder, CO, and closer to the Denver/Boulder u rban corridor than the higher site, Niwot, which lies 11.4 km northwest of Sugarloaf. and 1000 m higher in elevation. Key findings of this study are t hat Sugarloaf precipitation has the higher pH (less acidic) and lower condu ctivity of the two sites, and that different circulation patterns are assoc iated with different inter-site precipitation characteristics: chemistry, a mount, occurrence, and seasonal differences. Circulation indices account fo r about one-fourth to one-third of the variability in precipitation chemist ry, and synoptic scale circulation patterns are clearly different for extre mely low versus extremely high pH conditions at these two sites. (C) 2000 E lsevier Science Ltd. All rights reserved.