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Anthropogenic emissions of greenhouse gases and ozone-depleting substances are expected to continue to affect concentrations of ozone in the stratosphere through the 21st century. While a range of estimates for when stratospheric ozone is expected to return to unperturbed levels is available in the literature, quantification of the spread in results is sparse. Here we present the first probabilistic study of latitudinally resolved years of return of stratospheric ozone to 1960 levels. Results from our 180-member ensemble, simulated with a newly developed simple climate model, suggest that the spread in return years of ozone is largest around 40°N/S and in the southern high latitudes and decreases with increasing greenhouse gas emissions. The spread in projections of ozone is larger for higher greenhouse gas scenarios and is larger in the polar regions than in the midlatitudes, while the spread in ozone radiative forcing is smallest in the polar regions.

The longitudinal variability of the semidiurnal tide in the Antarctic upper mesosphere is investigated by comparison of observations from two radars at approximately opposite sides of Antarctica. Under the assumption that the tide is composed of an S = 2 (migrating) and S = 1 (westward-propagating, non-migrating) component only, the relative phases of the components are shown to vary with season such that the waves are typically in constructive interference during the winter (summer) months at longitudes around 0 degrees E (180 degrees E). We show that this has profound effects on the seasonal behaviour of the semidiurnal tide around 78 degrees S dependent on the longitude, and that no single-station observations at this latitude can be considered representative of a "zonal mean". The superposition of these two waves is used to interpret differences in previously-published ground-based climatologies of the tide. Citation: Hibbins, R. E., O. J. Marsh, A. J. McDonald, and M. J. Jarvis (2010), A new perspective on the longitudinal variability of the semidiurnal tide, Geophys. Res. Lett., 37, L14804, doi:10.1029/2010GL044015.

(1) This paper compares measurements in the Antarctic stratosphere during austral spring and summer made by the CHAMP radio-occultation satellite and in situ long-duration super-pressure balloon (SPB) observations during the Strateole/Vorcore campaign. Initial analysis compares near-simultaneous and co-located temperature observations made by these instruments and finds excellent agreement between these two very different sets of measurements. The mean bias between the data sets is � 0.52 K, CHAMP RO temperature being cooler than the balloon measurements, and the standard deviation of the temperature differences is 1.6 K for the paired observations. This paired data set also allows us to show that an empirical correction used to remove the influence of radiative heating on the balloon sensors does not produce any bias. An initial comparison of the magnitude of gravity wave activity observed by each instrument shows relatively poor agreement. Analysis suggests that this agreement can be improved slightly by accounting for the observational filtering associated with the CHAMP measurements. Citation: McDonald, A. J., and A. Hertzog (2008), Comparison of stratospheric measurements made by CHAMP radio occultation and Strateole/Vorcore in situ data,Geophys.Res.Lett.,35,L11805,doi:10.1029/2008GL033338.

[1] This study examines how the Renyi entropy statistical measure (RE; a generalization of Shannon entropy) can be applied to long-lived tracer data (e.g. methane), to understand mixing in the stratosphere. In order to show that RE can be used for this task we focus on the southern hemisphere stratosphere and the significant impact of the Antarctic polar vortex on the dynamics in this region. Using methane data from simulations of the chemistry-climate model SOCOL, we find clear patterns, consistent with those identified in previous studies of mixing. RE has the significant benefit that it is data driven and requires considerably less computational effort than other techniques. This initial study suggests that RE has a significant potential as a quantitative measure for analyzing mixing in the atmosphere.

[1] The signature of mid-latitude convection observed by a 46.5 MHz wind-profiling radar at Aberystwyth, UK (52.4°N, 4.0°W), is demonstrated by way of a case study. A key feature of such radars is their ability to measure the vertical air velocity directly, even under conditions of precipitation. Higher frequency radars, which have more typically been used for such studies, measure the net effect of hydrometeor terminal velocities and the air motion under such conditions. The radar is capable of observing both updrafts and downdrafts, with peak updrafts of the order of 10 m s−1. The signature of convection additionally consists of enhanced values of the radar return spectral width, which cannot be interpreted in terms of turbulence intensity, and reduced reliability of the corresponding radar-derived horizontal wind components. When convection reaches the uppermost troposphere, the radar return signal power can be anomalously large leading to the radar-derived tropopause altitude being overestimated. The presence of convection is confirmed by thermal infrared satellite imagery of high-topped clouds. Use is also made of radiosonde and UHF wind-profiler data.

[1] The dependence of Antarctic ozone depletion on midlatitude planetary wave activity and South Pole temperatures was examined from 1979–2003 using NCEP/NCAR reanalyses and column ozone data. The annual severity of Antarctic ozone depletion was quantified using the seasonal mean of daily ozone mass deficit (OMD). The dependence of annual mean OMD on effective equivalent stratospheric chlorine (EESC) was removed to produce an anomaly time series (OMD′). Similar anomaly time series for 100 hPa South Pole temperatures (T′) and 20 hPa, 60°S midlatitude planetary wave activity (PWA′) were calculated. Regression of OMD′ against T′ and PWA′ shows that most of the interannual variability in Antarctic ozone depletion can be explained by variability in midlatitude planetary wave activity and South Pole temperatures. To estimate how future changes in South Pole temperatures, midlatitude wave activity and EESC will affect Antarctic ozone depletion, the regression model was applied to T′ and PWA′ values from a chemistry-climate model run (1975–2019).