Mechanisms of stratospheric ozone depletion at high and middle latitudes

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Measurements of HF, HCl, ClONO2, HNO3, and O3 were made using the Ground-based FTIR instruments at Rikubetsu and Moshiri observatories on the island of Hokkaido, Japan, and at Kiruna Sweden since 1995. All these species observed in Japan show marked seasonal variations. Namely the column amounts are minimum in July-September and reach maximum values in February-April. These species are produced through photolysis of long lived trace species. The increases of the abundance of these species from fall to spring are basically due to poleward transport by planetary waves. In addition to the general increase of the column abundances in winter and spring, the variability is larger in these seasons. Based on the potential vorticity (PV) analysis, air mass in the polar vortex was occasionally transported to over the north part of Japan between February and April. On these cases, a decrease in the HCl/HF ratio and an increase in the ClONO2/HF ratio were observed. These results were consistent with those calculated using the three-dimensional chemistry and transport model (CTM) in which heterogeneous reactions on polar stratospheric clouds (PSCs) were included The observed day to day variation of O3 between January and April was generally in good agreement with that calculated using the CTM which included the heterogeneous reactions on PSCs. These CTM calculated O3 amounts were lower than those calculated without the heterogeneous reactions by 2 % at the end of March. When air mass in the polar vortex was transported to over Rikubetsu the difference was as large as 6 %. These results suggest the size of influence from the transport of air from the Arctic that was responsible for the ozone decrease observed at midlatitudes.