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In the extratropical atmosphere, Rossby waves (RWs) and internal gravity waves (GWs) propagating from the troposphere mediate a coupling with the middle atmosphere by influencing the dynamics therein. In state‐of‐the‐art chemistry‐climate models (CCMs), RW effects are well resolved while the majority of GW effects have to be parameterized. Here, we analyze orographic GW (OGW) interaction with resolved dynamics in a comprehensive CCM on daily time scales. For this, we apply a recently developed method of strong OGW drag event composites for three pronounced northern hemisphere OGW hotspots. We show that strong OGW drag events are associated with anomalous resolved wave propagation in the stratosphere. Causal links are inferred from previously published work and are supported by the anomalies in zonal circulation and wave activity tendencies. The nature of these anomalies varies depending on the hotspot region, which underlines the parameterized OGW‐resolved dynamics interaction being a two‐way process. Plain Language Summary: The majority of atmospheric waves are generated near the surface and propagate subsequently upward in the atmosphere. This includes Rossby waves that are resolved in climate models and small‐scale gravity waves (GWs) that commonly have to be parameterized. In the middle atmosphere, the waves eventually break, thereby dissipating their momentum and energy, which influences atmospheric dynamics. The interaction of GWs with the large‐scale circulation is to date poorly understood. In this study, we associate regionally enhanced GW drag with anomalies in resolved wave propagation in the stratosphere in a comprehensive chemistry‐climate model on the time scale of days. For this, we identify strong orographic GW (OGW) events for the three most pronounced northern hemisphere OGW hotspots and construct composites of anomalies of selected variables with respect to the climatological mean. We find that the response of the resolved wavefield strongly depends on the hotspot region, leading to diverse consequences on the large‐scale stratospheric circulation. Strong OGW events in the hotspots are in turn determined by the resolved fields from the surface to the level of OGW dissipation, which highlights the two‐way coupling between OGWs and resolved flow. Key Points: Intermittent parameterized orographic gravity wave drag affects stratospheric large‐scale dynamics in a chemistry‐climate modelDependence of the resolved dynamical response on the hotspot in question underlines the two‐way nature of the interactionUnsteady nature of the dynamical response sheds new light on how parameterized orographic gravity waves affect stratospheric transport [ABSTRACT FROM AUTHOR]

Dry deposition (DD) is a major loss process for tropospheric ozone and some reactive nitrogen and carbon precursors. We investigate the response of summertime ozone and its production chemistry over the Southeast United States (USA) to variability in this sink. Turning off DD of oxidized nitrogen, ozone, or all species over the United States in the Geophysical Fluid Dynamics Laboratory AM3 model increases regional mean surface ozone by 5, 18, or 25 ppb, respectively. Additional sensitivity simulations demonstrate that, assuming linearity, surface ozone has a similar sensitivity to ozone DD as to NOx emissions. Trends in ozone production efficiency derived from observed relationships between ozone and precursor oxidation products may not solely reflect precursor emission changes if ozone DD varies (e.g., with meteorology). We conclude that DD variability merits consideration when interpreting observed ozone trends. Quantifying the impact of changes in sinks versus sources will require long‐term DD measurements across the region of interest. Plain Language Summary: Ozone is an air pollutant near Earth's surface and a greenhouse gas higher in the atmosphere. While many studies consider which ozone sources should be controlled to reduce air pollution, we focus here on a poorly understood removal pathway, "dry deposition" (DD), to the Earth's surface. We use a model to quantify how ozone responds to changes in the DD of ozone and related gases (oxidized nitrogen and carbon gases). We find that a 50% decrease in DD changes ozone concentrations in the Southeast United States by at least as much as recent changes in national emissions of nitrogen oxides (which form ozone in the presence of sunlight and reactive carbon gases). Our model suggests that DD variability, potentially driven by changes in meteorology or land use, could affect surface ozone trends. However, we lack the observations that would allow an assessment of how DD changes over space and time. Key Points: A 50% decrease in ozone dry deposition has twice the effect on surface ozone over the Southeast USA as a 25% increase in NOx emissionsTwo different metrics for ozone production efficiency show opposite‐signed responses to shutting off ozone dry depositionBounding the influence of ozone dry deposition on tropospheric composition requires long‐term, regional observations of its variability [ABSTRACT FROM AUTHOR]

Simulated stratospheric temperatures over the period 1979–2016 in models from the Chemistry‐Climate Model Initiative are compared with recently updated and extended satellite data sets. The multimodel mean global temperature trends over 1979–2005 are −0.88 ± 0.23, −0.70 ± 0.16, and −0.50 ± 0.12 K/decade for the Stratospheric Sounding Unit (SSU) channels 3 (~40–50 km), 2 (~35–45 km), and 1 (~25–35 km), respectively (with 95% confidence intervals). These are within the uncertainty bounds of the observed temperature trends from two reprocessed SSU data sets. In the lower stratosphere, the multimodel mean trend in global temperature for the Microwave Sounding Unit channel 4 (~13–22 km) is −0.25 ± 0.12 K/decade over 1979–2005, consistent with observed estimates from three versions of this satellite record. The models and an extended satellite data set comprised of SSU with the Advanced Microwave Sounding Unit‐A show weaker global stratospheric cooling over 1998–2016 compared to the period of intensive ozone depletion (1979–1997). This is due to the reduction in ozone‐induced cooling from the slowdown of ozone trends and the onset of ozone recovery since the late 1990s. In summary, the results show much better consistency between simulated and satellite‐observed stratospheric temperature trends than was reported by Thompson et al. (2012, https://doi.org/10.1038/nature11579) for the previous versions of the SSU record and chemistry‐climate models. The improved agreement mainly comes from updates to the satellite records; the range of stratospheric temperature trends over 1979–2005 simulated in Chemistry‐Climate Model Initiative models is comparable to the previous generation of chemistry‐climate models. Plain Language Summary: A previous analysis by Thompson et al. (2012, https://doi.org/10.1038/nature11579) showed substantial differences between satellite‐observed and model‐simulated stratospheric cooling trends since the late 1970s. Here we compare recently revised and extended satellite temperature records with new simulations from 14 chemistry‐climate models. The results show much better agreement in the magnitude of stratospheric cooling over 1979–2005 between models and observations. This cooling was predominantly driven by increasing greenhouse gases and declining stratospheric ozone levels. An extended satellite temperature record and the chemistry‐climate models show weaker global stratospheric cooling over 1998–2016 compared to 1979–1997. This is due to the reduction in ozone‐induced cooling from the slowdown of ozone trends and the onset of ozone recovery since the late 1990s. There are larger differences in the latitudinal structure of past stratospheric temperature trends due to the effects of unforced atmospheric variability. In summary, the results show much better consistency between simulated and satellite‐observed stratospheric temperature trends than was reported by Thompson et al. (2012, https://doi.org/10.1038/nature11579) for the previous versions of the satellite record and last generation of chemistry‐climate models. The improved agreement mainly comes from updates to the satellite records, while the range of simulated trends is comparable to the previous generation of models. Key Points: There is substantial improvement in the comparison between modeled and observed stratospheric temperature trends over the satellite eraObservations and models show weaker stratospheric cooling since ~1998 when ozone‐depleting substances have been declining in the atmosphereLarger differences exist between modeled and observed stratospheric temperature trends at high latitudes partly due to internal variability [ABSTRACT FROM AUTHOR]