Figure showing distribution of the March total column ozone in the Northern Hemisphere extratropics for (a, c) long-term mean (climatology) and (b, d) Arctic ozone loss events.
Distribution of the March total column ozone in the Northern Hemisphere extratropics for (a, c) long-term mean (climatology) and (b, d) Arctic ozone loss events from the ERA5 and the historical run from CESM2-WACCM. An ozone loss example is simulated in March 1993 from the first historical run by CESM2-WACCM (c). The observed Arctic ozone loss events occurred in March of 1997, 2011, and 2020; only the 2011 case is shown for an observational example (d). Credit: Yu et al. [2022], Figure 1
Editors’ Highlights are summaries of recent papers in AGU’s journals and partner journals.
Source: Earth and Planetary Physics

Unlike the Antarctic ozone hole that forms every year in the austral spring, Arctic ozone is usually well above the ozone hole threshold of 220 Dobson Units. This is because the Arctic stratospheric vortex is usually too warm to form polar stratospheric clouds, which are the key for severe ozone depletion.

However, record breaking Arctic ozone loss was observed in spring 2020. Extremely cold air over the Arctic in the 2019-2020 winter was trapped in the polar vortex by anomalously strong westerly winds, resulting in an Arctic ozone loss event over an area equivalent to three Greenlands. In fact, since 1979, three extreme ozone-depletion events have been observed in the Arctic – in the boreal springs of 1997, 2011, and 2020. All three of these extreme ozone loss events were associated with a stratospheric polar vortex that was anomalously strong and cold.

Yu et al. [2022] extract the thermodynamic effects of Arctic ozone loss from the dynamic effects of the strong polar vortex state. They used a long-term dataset from a historical simulation by the CESM2-WACCM model to sort strong polar vortex events into those that were coupled and those that were uncoupled with atypical Arctic ozone loss.

They found that when a significant Arctic ozone loss event occurs the Northern Annular Mode (NAM) is significantly stronger in early spring than that associated with strong polar vortex events uncoupled to atypical Arctic ozone loss. Ozone loss in the Arctic is accompanied by increased ozone abundance in parts of the midlatitudes, especially over the North Pacific. The positive height anomalies partially due to diabatic heating processes associated with abundant ozone blockage in midlatitudes are stronger for Arctic ozone loss events than when ordinary strong polar vortex events are uncoupled to larger Arctic ozone loss. During atypical Arctic ozone loss events the positive height anomalies expand to cover almost the entire Arctic region, leading to an earlier and more rapid reversal of the NAM than when strong polar vortex events are uncoupled with atypical Arctic ozone loss.

Overall, the results suggest that the pure effect of ozone loss on the troposphere is still robust even in the absence of an anomalously strong polar vortex. This research also finds that the effect of Arctic ozone loss on stratosphere-troposphere temperature variability can be explained by the geographical redistribution of where solar shortwave radiation is absorbed by the ozone. In contrast, for ordinary strong polar vortex events uncoupled with atypical Arctic ozone loss, the direct effect by the thermodynamic processes and the corresponding near surface temperature anomalies are much weaker and less significant.

Citation: Yu, S. Y., Rao, J., and Guo, D. (2022). Arctic ozone loss in early spring and its impact on the stratosphere-troposphere coupling. Earth and Planetary Physics, 6(2), 177–190.

—Yan Xia, Science Writer

Editor’s Note: Earth and Planetary Physics is an AGU partner journal; it is co-sponsored by the Chinese Geophysical Society, the Institute of Geology and Geophysics of the Chinese Academy of Sciences, and Science Press.

Text © 2022. The authors. CC BY-NC-ND 3.0
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