Abstract
AbstractOzone depletion led to a positive trend in the summertime Southern Annular Mode (SAM) during the last decades of the 20th century. During the present century, global warming (GW) is expected to contribute to a positive SAM trend while ozone recovery is expected to act in the opposite direction. Here, Southern Hemisphere (SH) circulation and regional precipitation change are studied with a methodology that separates the effects from GW and ozone depletion/recovery. Our results show that a “tug‐of‐war” between ozone and GW occurs in the summertime stratosphere, propagating to the troposphere where it is manifest in the SAM. However, at the regional scale this “tug‐of‐war” is not as relevant as the combined effects of other remote drivers of circulation change, which force different kinds of precipitation changes in the SH. For regional precipitation changes, the uncertainty in future circulation change is as important as the uncertainty in the GW level.
Highlights
Both observational (Randel & Wu, 1999; Young et al, 2013) and modeling (Arblaster & Meehl, 2006; McLandress et al, 2010; Stolarski et al, 2010) studies have shown a clear cooling in the Antarctic lower stratosphere in late-spring during the last decades of the 20th century associated with ozone depletion
Our results show that a “tug-of-war” between ozone and global warming (GW) occurs in the summertime stratosphere, propagating to the troposphere where it is manifest in the Southern Annular Mode (SAM)
We find that the slp changes per day of vortex breakdown delay (VBdelay) south of 40°S are very similar between GW and effective stratospheric chlorine (EESC), with the response to EESC forcing being more zonally symmetric
Summary
Both observational (Randel & Wu, 1999; Young et al, 2013) and modeling (Arblaster & Meehl, 2006; McLandress et al, 2010; Stolarski et al, 2010) studies have shown a clear cooling in the Antarctic lower stratosphere in late-spring during the last decades of the 20th century associated with ozone depletion. Global warming is expected to lead to similar changes in the westerlies (Kushner et al, 2001), ozone recovery can be expected to act in the opposite sense (Son et al, 2010) How this “tug-of-war” on the SAM evolves during the 21st century will have significant impacts for Southern Hemisphere (SH) regional climate. The goal of this study is to extend the approach of Mindlin et al (2020) to include the effect of both global warming and ozone depletion/recovery on the SPV breakdown, and thereby on regional SH climate, testing the hypothesis of the “tug-of-war” occurring in the stratosphere We do this by taking into account both drivers of the SPV breakdown delay together with tropical upper-tropospheric warming, and constructing time-dependent storylines for SH circulation and regional precipitation changes associated with different responses of the remote drivers to anthropogenic forcings. We can describe the spread in the Coupled Model Intercomparison Project Phase 6 (CMIP6) models in a physically interpretable way
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