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Abstract. The connection between the dominant mode of interannual variability in the tropical troposphere, El Nino Southern Oscillation (ENSO), and entry of stratospheric water vapor, is analyzed in a set of the model simulations archived for the Chemistry-Climate Model Initiative (CCMI) project and for phase 6 of the Coupled Model Intercomparison Project. While the models agree on the temperature response to ENSO in the tropical troposphere and lower stratosphere, and all models also agree on the zonal structure of the response in the tropical tropopause layer, the only aspect of the entry water vapor with consensus is that La Nina leads to moistening in winter relative to neutral ENSO. For El Nino and for other seasons there are significant differences among the models. For example, some models find that the enhanced water vapor for La Nina in the winter of the event reverses in spring and summer, other models find that this moistening persists, while some show a nonlinear response with both El Nino and La Nina leading to enhanced water vapor in both winter, spring, and summer. Focusing on Central Pacific ENSO versus East Pacific ENSO, or temperatures in the mid-troposphere as compared to temperatures near the surface, does not narrow the inter-model discrepancies. Despite this diversity in response, the temperature response near the cold point can explain the response of water vapor when each model is considered separately. While the observational record is too short to fully constrain the response to ENSO, it is clear that most models suffer from biases in the magnitude of interannual variability of entry water vapor. This bias could be due to missing forcing processes that contribute to observed variability in cold point temperatures.

<p>The connection between the dominant mode of interannual variability in the tropical troposphere, El Niño Southern<br>Oscillation (ENSO), and entry of stratospheric water vapor, is analyzed in a set of the model simulations archived for the<br>Chemistry-Climate Model Initiative (CCMI) project and for phase 6 of the Coupled Model Intercomparison Project. While the<br>models agree on the temperature response to ENSO in the tropical troposphere and lower stratosphere, and all models also agree<br> on the zonal structure of the response in the tropical tropopause layer, the only aspect of the entry water vapor with consensus<br>is that La Niña leads to moistening in winter relative to neutral ENSO. For El Niño and for other seasons there are significant<br>differences among the models. For example, some models find that the enhanced water vapor for La Niña in the winter of the<br>event reverses in spring and summer, other models find that this moistening persists, while some show a nonlinear response<br>with both El Niño and La Niña leading to enhanced water vapor in both winter, spring, and summer. A moistening in the spring<br> following El Niño events, perhaps the strongest signal in observations, is simulated by only half of the models. Focusing on<br>Central Pacific ENSO versus East Pacific ENSO, or temperatures in the mid-troposphere as compared to temperatures near the<br>surface, does not narrow the inter-model discrepancies. Despite this diversity in response, the temperature response near the<br>cold point can explain the response of water vapor when each model is considered separately. While the observational record is<br>too short to fully constrain the response to ENSO, it is clear that most models suffer from biases in the magnitude of interannual<br>variability of entry water vapor. This bias could be due to biased cold point temperatures in some models, but others appear to<br>be missing forcing processes that contribute to observed variability near the cold point</p>

The Northern Hemisphere and tropical circulation response to interannual variability in Arctic stratospheric ozone is analyzed in a set of the latest model simulations archived for the Chemistry-Climate Model Initiative (CCMI) project. All models simulate a connection between ozone variability and temperature/geopotential height in the lower stratosphere similar to that observed. A connection between Arctic ozone variability and polar cap surface air pressure is also found, but additional statistical analysis suggests that it is mediated by the dynamical variability that typically drives the anomalous ozone concentrations. While the CCMI models also show a connection between Arctic stratospheric ozone and the El Niño-Southern Oscillation (ENSO), with Arctic stratospheric ozone variability leading to ENSO variability 1 to 2 years later, this relationship in the models is much weaker than observed and is likely related to ENSO autocorrelation rather than any forced response to ozone. Overall, Arctic stratospheric ozone is related to lower stratospheric variability. Arctic stratospheric ozone may also influence the surface in both polar and tropical latitudes, though ozone is likely not the proximate cause of these impacts and these impacts can be masked by internal variability if data are only available for ∼ 40 years.Published by Copernicus Publications on behalf of the European Geosciences Union.