Zonally asymmetric trends of winter total column ozone in the northern middle latitudes

Abstract

Using various satellite-based observations, a linear ozone transport model (LOTM), a chemistry-climate model (WACCM3) and an offline chemical transport model (SLIMCAT), zonally asymmetric trends of the total column ozone (TCO) in the northern middle latitudes during winter for the period 1979-2015 are analyzed and factors responsible for the trends are diagnosed. The results reveal that there are significant negative TCO trends over the North Pacific and positive TCO trends over the northwestern North America. The zonally asymmetric TCO trends are mainly contributed by the trends in partial column ozone in the upper troposphere and lower stratosphere (UTLS) which are closely related to the long-term changes of geopotential height in the troposphere. Furthermore, the trends of geopontential height in the UTLS are mainly modulated by pattern changes in the Arctic Oscillation (AO), the Cold Ocean-Warm Land (COWL) and the North Pacific (NP) index. Accordingly, the zonally asymmetric TCO trends can be largely reconstructed by the trends of the above three teleconnection patterns. Sea surface temperature (SST) changes over the Pacific Ocean and the Atlantic Ocean can also exert a significant contribution to the zonally asymmetric TCO trends through their influence on the COWL and NP patterns. In addition, chemical ozone loss partially offsets the positive trends in zonal TCO anomalies over Central Siberia and enhances the positive TCO trends over northwestern North America. However, the contribution of chemical processes to the zonally asymmetric TCO trends is relatively smaller than that of dynamical transport effects. Interpreting the zonally asymmetric TCO trends and their responsible factors would be helpful for accurately predicting the stratospheric ozone return date in the northern middle latitudes.

The Influence of Zonally Asymmetric Stratospheric Ozone Changes on the Arctic Polar Vortex Shift

“…Compared to the TCO trends in January and March, the trends in TCO in February show a more asymmetric structure in the high latitudes with a strong TCO decline over Siberia. This feature is consistent with the conclusion of Zhang et al (2016Zhang et al ( , 2018Zhang et al ( , 2019b) that the shift of the Arctic stratospheric polar vortex toward Eurasia is more significant in February. Considering that the most significant ZAO trend occurs in February, we will now focus on the impacts of ZAO changes on the polar vortex in that month.…”

“…Using numerical model simulations, most previous studies only found significant regional surface responses over the northern middle and high latitudes when comparing cases of extremely high and low Arctic stratospheric ozone (Cheung et al 2014;Karpechko et al 2014;Smith and Polvani 2014;Calvo et al 2015;Xie et al 2016Xie et al , 2017Harari et al 2019). One possible reason is that the dynamical variability of the Arctic stratospheric polar vortex is much larger than its Antarctic counterpart (Hu and Guan 2018;Hu et al 2019a;Mai et al 2020) and as a result Arctic stratospheric ozone depletion is less persistent than Antarctic ozone depletion (Manney et al 2011). Therefore, one would expect a weaker impact of ozone depletion on surface conditions in the Northern Hemisphere compared to the Southern Hemipshere.…”

“…Although the above-mentioned studies revealed that stratospheric ozone variations and its zonally asymmetric component can alter polar vortex strength, little is known regarding the effects of stratospheric ozone changes on stratospheric polar vortex position. Zhang et al (2016) found that the Arctic stratospheric polar vortex has been shifted toward Siberia during late winter over the period 1980-2015. They attributed the shift of the stratospheric polar vortex to enhanced upward propagation of baroclinic waves associated with Arctic sea ice loss and increased Siberian snow cover.…”

“…One purpose of this study is to verify this hypothesis. Zhang et al (2018) pointed out that the stratospheric polar vortex shift could transport air, which is both ozone-poor and high in active chlorine, from the Arctic regions to the Eurasian continent, leading to a ZAO structure with a stronger total column ozone (TCO) decline over Eurasia than over other regions at the same latitudes. This conclusion suggests that the polar vortex shift could further enhance the ZAO structure in the middle and high latitudes.…”

Decreases in wintertime total column ozone over the Tibetan Plateau during 1979–2017

“…Also, following the implementation of the Montreal Protocol in 1987, signs of an ozone recovery have been reported in recent years (WMO,70 2014; Chipperfield et al, 2015Chipperfield et al, , 2017Solomon et al, 2016;Kuttippurath and Nair, 2017;Pazmiño et al, 2018;Strahan and Douglass, 2018;Weber et al, 2018). Outside of the polar regions, column ozone amounts are largely determined by the stratospheric dynamics and hence quantifying long-term trends is quite challenging Rex et al, 2004;Manney et al, 2011;Zhang et al, 2016Zhang et al, , 2018Zhang et al, , 2019. Observations and model simulations 75…”