Ground-Based Inversion Frequencies Determined from Surface Climatological Data

Engineering air pollution dispersion studies sometimes require a knowledge of the frequency of occurrence of ground-based inversions. Hostler (1961) and Munn et al. (1970) have prepared maps of frequencies of ground-based inversions for the United States and Canada, respectively, using radiosonde data. The method presented here employs long-term climatological maximum and minimum temperature data recorded at 36 pairs of valley/ridge climatological stations in British Columbia with at least several years of coincident data. Daily maximum and daily minimum temperatures at each pair of stations were compared. Monthly totals of positive temperature differences, i.e., inversion occurrences, in these comparisons were totalled, and converted to seasonal percentages, over the period of record. The resulting seasonal sets of inversion percentages at the times of maximum and minimum temperature are tabled. The effects of station separation, both horizontally and vertically are discussed, and the influence of adjacent water bodies, acting as heat sources in winter and heat sinks in summer are illustrated. Comparisons with the results obtained by other investigators are made.