Description: Analysis of the variability of equatorial ozone profiles in the Satellite Aerosol and Gas Experiment-corrected Solar Backscatter Ultraviolet data set demonstrates a strong seasonal persistence of interannual ozone anomalies, revealing a seasonal dependence to equatorial ozone variability. In the lower stratosphere (40–25 hPa) and in the upper stratosphere (6–4 hPa), ozone anomalies persist from approximately November until June of the following year, while ozone anomalies in the layer between 16 and 10 hPa persist from June to December. Analysis of zonal wind fields in the lower stratosphere and temperature fields in the upper stratosphere reveals a similar seasonal persistence of the zonal wind and temperature anomalies associated with the quasi-biennial oscillation (QBO). Thus, the persistence of interannual ozone anomalies in the lower and upper equatorial stratosphere, which are mainly associated with the well-known QBO ozone signal through the QBO-induced meridional circulation, is related to a newly identified seasonal persistence of the QBO itself. The upper stratospheric QBO ozone signal is argued to arise from a combination of QBO-induced temperature and NOx perturbations, with the former dominating at 5 hPa and the latter at 10 hPa. Ozone anomalies in the transition zone between dynamical and photochemical control of ozone (16–10 hPa) are less influenced by the QBO signal and show a quite different seasonal persistence compared to the regions above and below.

Description: Interannual anomalies in vertical profiles of stratospheric ozone, in both equatorial and extratropical regions, have been shown to exhibit a strong seasonal persistence, namely, extended temporal autocorrelations during certain times of the calendar year. Here we investigate the relationship between this seasonal persistence of equatorial and extratropical ozone anomalies using the SAGE-corrected SBUV data set, which provides a long-term ozone profile time series. For the regions of the stratosphere where ozone is under purely dynamical or purely photochemical control, the seasonal persistence of equatorial and extratropical ozone anomalies arises from distinct mechanisms but preserves an anticorrelation between tropical and extratropical anomalies established during the winter period. In the 16–10 hPa layer, where ozone is controlled by both dynamical and photochemical processes, equatorial ozone anomalies exhibit a completely different behavior compared to ozone anomalies above and below in terms of variability, seasonal persistence, and especially the relationship between equatorial and extratropical ozone. Cross-latitude-time correlations show that for the 16–10 hPa layer, Northern Hemisphere (NH) extratropical ozone anomalies show the same variability as equatorial ozone anomalies but lagged by 3–6 months. High correlation coefficients are observed during the time frame of seasonal persistence of ozone anomalies, which is June–December for equatorial ozone and shifts by approximately 3–6 months when going from the equatorial region to NH extratropics. Thus in the transition zone between dynamical and photochemical control, equatorial ozone anomalies established in boreal summer/autumn are mirrored by NH extratropical ozone anomalies with a time lag similar to transport time scales. Equatorial ozone anomalies established in boreal winter/spring are likewise correlated with ozone anomalies in the Southern Hemisphere extratropics with a time lag comparable to transport time scales, similar to what is seen in the NH. However, the correlations between equatorial and SH extratropical ozone in the 10–16 hPa layer are weak.

Description: The role of the stratosphere in tropospheric climate response to increased concentrations of the greenhouse gases during Northern Hemisphere winter is addressed by performing and analyzing a set of simulations with the atmosphere general circulation model ECHAM5. Attention is paid to the difference in the response to doubled CO2 concentration and associated sea surface temperature and sea ice concentration anomaly between a low-top and a stratosphere-resolving model version. We find a larger decrease of the Arctic sea level pressure in late winter in the low-top model when compared to the stratosphere-resolving one. Such dependence of the response on the representation of the stratosphere is consistent with previous multimodel results, indicating that the difference is likely robust across different models. The different response of the tropospheric circulation may have important climatic consequences; for example, we demonstrate a different precipitation response over Europe in these experiments. The different tropospheric response is shown to originate from different response in the polar stratosphere which is attributable to a stronger Brewer-Dobson circulation response in the stratosphere-resolving model. A decomposition of the Brewer-Dobson circulation response to contributions from resolved and parameterized processes show that both contribute toward the stronger downwelling response in the polar stratosphere in the stratosphere-resolving model. Additional sensitivity experiments reveal that the magnitude of the Arctic sea level pressure response, but not the difference between the stratosphere-resolving and low-top model responses, depends on the magnitude of SST anomaly in the tropical Pacific.