The radiative effects of polar ozone depletion act to cool and strengthen the stratospheric polar vortex (Randel & Wu, 1999;Waugh et al., 1999), and dynamical coupling between the stratosphere and troposphere acts to connect the changes in the stratospheric flow to the surface (Baldwin & Dunkerton, 2001;Thompson et al., 2005). At the surface, the changes in the flow associated with the ozone hole project onto the southern annular mode (Shindell & Schmidt, 2004;Thompson & Solomon, 2002). Thus the ozone hole has been linked to long-term changes in surface climate that span much of the Southern Hemisphere mid and high latitudes.The linkages between the Antarctic ozone hole and the SAM are important for the interpretation of Southern Hemisphere climate change. Over the 1970-1990s, the development of the ozone hole was associated with widespread changes in Southern Hemisphere surface climate that are consistent with forcing by ozone depletion (Thompson et al., 2011). Paleoclimate studies indicate that the resulting changes in the austral summer SAM index are unprecedented over the last thousand years, pointing toward the remarkable role of the ozone hole in Southern Hemisphere climate change (Fogt & Marshall, 2020).In recent years, the Antarctic ozone hole has exhibited signs of healing consistent with recent decreases in anthropogenic emissions of ozone-depleting substances (Solomon et al., 2016). The healing of the ozone hole is apparent when viewed in the context of decades, especially during September when dynamic variability in the vortex is modest (

Observations reveal two distinct patterns of atmospheric variability associated with wintertime variations in midlatitude sea surface temperatures (SST) in the North Pacific sector: 1) a pattern of atmospheric circulation anomalies that peaks 2-3 weeks prior to large SST anomalies in the western North Pacific that is consistent with “atmospheric forcing” of the SST field, and 2) a pattern that lags SST anomalies in the western North Pacific by several weeks that is consistent with the “atmospheric response” to the SST field. Here we explore analogous lead-lag relations between the atmospheric circulation and western North Pacific SST anomalies in two sets of simulations run on the NCAR Community Earth System Model Version 1 (CESM1): 1) a simulation run on a fully coupled version of CESM1 and 2) a simulation forced with prescribed, time-evolving SST anomalies over the western North Pacific region. Together, the simulations support the interpretation that the observed lead/lag relationships between western North Pacific SST anomalies and the atmospheric circulation reveal the patterns of atmospheric variability that both force and respond to midlatitude SST anomalies. The results provide numerical evidence that SST variability over the western North Pacific has a demonstrable effect on the large-scale atmospheric circulation throughout the North Pacific sector.

The purpose of this study is to quantify the effects of coupled chemistry–climate interactions on the amplitude and structure of stratospheric temperature variability. To do so, the authors examine two simulations run on version 4 of the Whole Atmosphere Coupled Climate Model (WACCM): a “free-running” simulation that includes fully coupled chemistry–climate interactions and a “specified chemistry” version of the model forced with prescribed climatological-mean chemical composition. The results indicate that the inclusion of coupled chemistry–climate interactions increases the internal variability of temperature by a factor of ~2 in the lower tropical stratosphere and—to a lesser extent—in the Southern Hemisphere polar stratosphere. The increased temperature variability in the lower tropical stratosphere is associated with dynamically driven ozone–temperature feedbacks that are only included in the coupled chemistry simulation. The results highlight the fundamental role of two-way feedbacks between the atmospheric circulation and chemistry in driving climate variability in the lower stratosphere.

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