Climate variability and tropospheric ozone depletion in the Arctic spring

We investigated the frequency of Arctic Ozone Depletion Events (ODEs) and its relationships to the northern hemispheric modes of climate variability in the past 30 years. The frequency of ODEs was diagnosed using surface ozone measurements at three monitoring sites in the Arctic (Barrow, Alert, and Zeppelinfjellet), which showed large inter-annual variations. Among the various climate variability indices, ODE frequencies at Barrow and Alert have the largest correlations with the Western Pacific (WP) index. Strong ODEs are associated with the negative phase of WP index, reduced extension of the jet stream from the Pacific and weakened Pacific storm track. Reduced transport of O3-rich air masses and more in situ halogen-driven loss are possible reasons. ODE frequencies at Zeppelinfjellet, on the other hand, have a weaker correlation with the WP index. In the past 30 years, the occurrences of ODEs at all three sites were more frequent in the 1990s, coinciding with the larger negative WP index in that decade compared to 1980s and 2000s.