[1] Simulations of the stratosphere from thirteen coupled chemistry-climate models (CCMs) are evaluated to provide guidance for the interpretation of ozone predictions made by the same CCMs. The focus of the evaluation is on how well the fields and processes that are important for determining the ozone distribution are represented in the simulations of the recent past. The core period of the evaluation is from 1980 to 1999 but long-term trends are compared for an extended period . Comparisons of polar high-latitude temperatures show that most CCMs have only small biases in the Northern Hemisphere in winter and spring, but still have cold biases in the Southern Hemisphere spring below 10 hPa. Most CCMs display the correct stratospheric response of polar temperatures to wave forcing in the Northern, but not in the Southern Hemisphere. Global long-term stratospheric temperature trends are in reasonable agreement with satellite and radiosonde observations. Comparisons of simulations of methane, mean age of air, and propagation of the annual cycle in water vapor show a wide spread in the results, indicating differences in transport. However, for around half the models there is reasonable agreement with observations. In these models the mean age of air and the water vapor tape recorder signal are generally better than reported in previous model intercomparisons. Comparisons of the water vapor and inorganic chlorine (Cl y ) fields also show a large intermodel spread. Differences in tropical water vapor mixing ratios in the lower stratosphere are primarily related to biases in the simulated tropical tropopause temperatures and not transport. The spread in Cl y , which is largest in the polar lower stratosphere, appears to be primarily related to transport differences. In general the amplitude and phase of the annual cycle in total ozone is well simulated apart from the southern high latitudes. Most CCMs show reasonable agreement with observed total D223081 of 29 ozone trends and variability on a global scale, but a greater spread in the ozone trends in polar regions in spring, especially in the Arctic. In conclusion, despite the wide range of skills in representing different processes assessed here, there is sufficient agreement between the majority of the CCMs and the observations that some confidence can be placed in their predictions. Citation: Eyring, V., et al. (2006), Assessment of temperature, trace species, and ozone in chemistry-climate model simulations of the recent past,

Simulations from eleven coupled chemistry‐climate models (CCMs) employing nearly identical forcings have been used to project the evolution of stratospheric ozone throughout the 21st century. The model‐to‐model agreement in projected temperature trends is good, and all CCMs predict continued, global mean cooling of the stratosphere over the next 5 decades, increasing from around 0.25 K/decade at 50 hPa to around 1 K/decade at 1 hPa under the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emissions Scenarios (SRES) A1B scenario. In general, the simulated ozone evolution is mainly determined by decreases in halogen concentrations and continued cooling of the global stratosphere due to increases in greenhouse gases (GHGs). Column ozone is projected to increase as stratospheric halogen concentrations return to 1980s levels. Because of ozone increases in the middle and upper stratosphere due to GHG‐induced cooling, total ozone averaged over midlatitudes, outside the polar regions, and globally, is projected to increase to 1980 values between 2035 and 2050 and before lower‐stratospheric halogen amounts decrease to 1980 values. In the polar regions the CCMs simulate small temperature trends in the first and second half of the 21st century in midwinter. Differences in stratospheric inorganic chlorine (Cly) among the CCMs are key to diagnosing the intermodel differences in simulated ozone recovery, in particular in the Antarctic. It is found that there are substantial quantitative differences in the simulated Cly, with the October mean Antarctic Cly peak value varying from less than 2 ppb to over 3.5 ppb in the CCMs, and the date at which the Cly returns to 1980 values varying from before 2030 to after 2050. There is a similar variation in the timing of recovery of Antarctic springtime column ozone back to 1980 values. As most models underestimate peak Cly near 2000, ozone recovery in the Antarctic could occur even later, between 2060 and 2070. In the Arctic the column ozone increase in spring does not follow halogen decreases as closely as in the Antarctic, reaching 1980 values before Arctic halogen amounts decrease to 1980 values and before the Antarctic. None of the CCMs predict future large decreases in the Arctic column ozone. By 2100, total column ozone is projected to be substantially above 1980 values in all regions except in the tropics.

Abstract. Gravity waves in the lower polar stratosphere are examined using operational radiosonde observations gathered from 33 stations over a period of 10 years. Both the potential and kinetic energies of the gravity waves vary annually and reach maxima in winter in the Arctic and in spring in the Antarctic. In the Antarctic spring a region of large gravity wave energy propagates downward following the movement of a zone of high static stability associated with Southern Hemispheric warming. Moreover, the enhanced energy region and the high stability zone coincide in the horizontal plane and move gradually from 135øE, 50øS to 45øW, 70øS over the South Pole. The vertical and horizontal directions of wave propagation are examined using hodograph analysis in the vertical. Most gravity waves transfer energy upward in the Arctic, while the percentage of downward energy propagation is relatively high in winter and spring in the Antarctic. Horizontally, gravity waves propagate westward relative to the mean wind in the Arctic, while in the Antarctic the dominant direction varies from station to station. The correlation between gravity wave energy in the lower stratosphere and the mean wind is also examined. In the Arctic, gravity wave energy is highly correlated with the surface wind, though in the Antarctic it correlates with the stratospheric wind. These results suggest that gravity waves observed in the Arctic are forced by topography, whereas in Antarctica some sources may exist in the stratosphere. One such source candidate is likely to be the polar night jet.

Intensive radiosonde observations were performed at Syowa Station (69.0°S, 39.6°E) over about 10 days in each of March, June, October, and December 2002 to examine inertia-gravity wave characteristics in the Antarctic lower stratosphere. Based on the 3-hourly observation data, two-dimensional (i.e., vertical wavenumber versus frequency) spectra of wind fluctuations were examined, utilizing a double Fourier transform method. Clear signals of gravity waves whose phases propagate upward, suggesting downward energy propagation, are detected in June and October when the polar night jet (PNJ) was present. On the other hand, downward phase propagation (i.e., upward energy propagation) components are dominant in all months. There is a spectral peak around the inertial frequency in a wide range of vertical wavenumbers in December when the background wind was weak, whereas large spectral densities are distributed over lower-frequency regions in June and October. These spectral characteristics are consistent with the results obtained using a gravity wave-resolving global circulation model (GCM) by Sato et al. Dynamical characteristics are examined separately for upward-and downward-propagating gravity waves in June, using a hodograph analysis method. As a result, it is found that upward-and downward-propagating wave packets observed simultaneously in the same height regions have similar horizontal wavelengths and phase velocities. This fact suggests that these gravity waves are generated from the same source with a similar mechanism. When the wave packets were observed, both the local Rossby number and the residual in the nonlinear balance equation estimated using NCEP-NCAR reanalysis data are large around the PNJ situated slightly to the lower latitudes of Syowa Station. Therefore, it is likely that the observed inertia-gravity waves are generated by a spontaneous adjustment around the geostrophically unbalanced PNJ and propagate toward Syowa Station. The possibility of spontaneous gravity wave generation around the PNJ is confirmed by comparison with the GCM simulation by Sato et al.

[1] Gravity waves in the Antarctic lower stratosphere are examined using original operational radiosonde data obtained at Syowa Station (69.0°S, 39.6°E) with fine vertical resolution. In the lower stratosphere the temporal variation in gravity wave energy depends on height. In the height region of 13-15 km, just above the tropopause, the seasonal variation in gravity wave energy is not evident. The wave energy is rather enhanced when the absolute value of potential vorticity in the upper troposphere becomes small over Syowa Station. This fact implies that tropospheric disturbances affect the dynamical processes of gravity waves there. However, the gravity wave energy in the height region of 15-25 km shows clear seasonal variation having a maximum in spring. The time variation in gravity wave energy is examined in detail in terms of the polar vortex by using the equivalent latitude coordinate. Energy enhancements occur when the edge of the polar vortex approaches Syowa Station, and the enhancements are especially large when the polar vortex breaks down in spring. These results suggest that height variation in the background atmosphere leads to the difference of wave characteristics between the two height regions. The enhancements of wave energy are partly explained as modification of the wave structure by the background wind speed and the static stability, but it is also likely that enhancements of wave activity contribute to the energy enhancement at the edge of the polar vortex in spring.

. The CCM calculations are performed with the two ensemble members for REF1 scenario of the chemistry climate model validation (CCMVal) and the one ensemble member for the REF2 scenario. CCM simulates the development of the ozone hole from 1982 to 2000, as observed with a total ozone mapping spectrometer (TOMS), although the year-to-year variation is different from the observation owing to the internal variability of CCM and the ozone decreasing trends of CCM ozone in the two ensemble members of REF1 are underestimated. The trends in temperature and zonal mean zonal wind are analyzed and compared with the observations. There is consistency among the trends in zonal mean temperature, zonal mean zonal wind, and total ozone, but they differ among the ensemble members and observations. The diabatic heating rates and Eliassen-Palm flux fields are investigated in order to explain the differences. A delay trend in the breakup time of the Antarctic polar vortex is obtained for the period of 1980-1999 in the NCEP/ NCAR and ERA40 data. A similar trend is also obtained from the CCM simulations, with statistical significance in one ensemble member of REF1 and REF2. Because the trends of the observations in the EP flux from the troposphere and its deposition in the lower stratosphere are consistent with an advanced breakup date of the polar vortex and because the trends of the CCM simulations are very small, it is likely that the Antarctic ozone depletion had some effect on the delay during the period 1980 . From 2000, the NCEP/NCAR data show a large variation in breakup time, which makes the delay trend much less important. It is likely that the large variation in wave flux masked the effects of the ozone loss during that period. The two ensemble members of the REF1 simulation do not show such a dramatic change in the trend for the period 2000-2004, whereas REF2 shows a change in the trend for that period.

[1] We examine the effect of polar vortex processing on ozone concentrations outside the 1997 Arctic polar vortex. The Arctic vortex in this year was well isolated, cold, and circumpolar, and it broke up unusually late. However, time threshold diagnostics (TTD) analysis using a middle vortex boundary defined by the first derivative of the equivalent latitude gradient of potential vorticity and calculations using the nudging chemical transport model (CTM) of the Center for Climate System Research/National Institute for Environmental Studies (CCSR/NIES) show that there were intermittently several relatively large transport events from the vortex to the outside region in the lower stratosphere, with timescales and spatial scales that can be resolved at T42 CTM horizontal resolution (2.8°by 2.8°grid). These intermittent outflow events of polar air are also identified in TTD analysis using an outer vortex boundary defined by the second derivative of potential vorticity and a boundary defined by the N 2 O concentration. These intermittent events had a significant effect on the ozone concentration outside the vortex near the boundary in this year. A CTM calculation with a polar chemical ozone tracer shows that the effect on the ozone concentration outside the polar vortex near the vortex boundary in the equivalent latitude band of 55°-65°N and 450 K is 0.3 ppmv (15-20% of the ozone concentration at this height) and that on the total ozone is 12-15 Dobson units (1 DU = 0.001 atm cm) (3-4% of the total ozone) by the end of April just before the final vortex breakup. The effect in the equivalent latitude band of 30°-60°N is much smaller, with a reduction of 2 DU at the end of March and 4 DU by the end of April (less than 1% of the total ozone). The effect is about the half if we use the inner boundary or a boundary of 73°N equivalent latitude for the polar tracer calculations. The CTM calculations also show that these polar vortex processing effects might be masked at midlatitudes by the local gas phase chemical ozone production/loss reactions after mid-April at 450 K and earlier than those at 500 K.

An intensive radiosonde observation with time intervals of 3 h was performed in June 2002 at Syowa Station (39.6 E, 69 S) in the Antarctic. A wavelike disturbance with a wave period of 12-15 h, having a nearly barotropic structure was observed above a height of 22 km in the time period of 27-28 June 2002. A result of the hodograph analysis suggests that the short-period disturbance is not due to an inertiagravity wave. A similar short-period disturbance is observed in the European Centre for Medium-Range Weather Forecasts (ECMWF) operational analysis data. Results of detailed analysis using the ECMWF data show that the short-period disturbance has a horizontal wavelength of about 2000 km, and propagates along a potential vorticity minimum region with a horizontal phase velocity of about 40 m s À1 . This phase velocity is equal to the background horizontal wind velocity at the potential vorticity minimum. A necessary condition for the barotropic instability is locally satisfied at the potential vorticity minimum. However, it is rather appropriate that the short-period disturbance is interpreted as a neutral wave than as an unstable wave in the barotropically unstable background flow. This result implies any unknown mechanism of the suppression of barotropic instability in the locally unstable background flow associated with a disturbed polar vortex.