Arctic ozone loss in early spring and its impact on the stratosphere-troposphere coupling

The tropospheric impact of Arctic ozone loss events is still debatable. In this study we investigate that question, using the ERA5 reanalysis and long-term integration by a climate-chemistry coupled model (CESM2-WACCM). We begin with the frequency of Arctic ozone loss events. On average, such events occur once in early spring every 14−15 years in ERA5 data and in the model, both of which estimate that roughly 40% of the strong polar vortex events in March are coupled with Arctic ozone loss, the remaining 60% being uncoupled. The composite difference between the two samples might be attributed to the pure impact of the Arctic ozone loss — that is, to ozone loss alone, without the concurrent impact of strong polar vortices. Arctic ozone loss is accompanied by an increase in total ozone in midlatitudes, with the maximum centered in the Central North Pacific. Contrasting Arctic ozone loss events with pure strong polar vortex events that are uncoupled with ozone loss, observations confirm that the stratospheric Northern Annular Mode reverses earlier for the former. For pure strong vortex events in early spring (without Arctic ozone loss), the cold anomalies can extend from the stratosphere to the middle troposphere; when such events are strong, the near surface warm anomalies are biased toward the continents. In contrast, during the other 40% of strong early-spring polar vortex events, those coupled with ozone loss, a concurrent and delayed warming of the near surface over the Arctic and its neighboring areas is observed, due to vertical redistribution of solar radiation by the change in the ozone.