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Department of Meteorology, University of Reading, Reading, UK
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- PublicationRestrictedAspects of stratospheric long-term changes induced by ozone depletion(2006)
; ; ; ;Cagnazzo, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Claud, C.; Laboratoire de Me´ te´ orologie Dynamique du CNRS, Institut Pierre et Simon Laplace (IPSL), Ecole Polytechnique ;Hare, S.; Department of Meteorology, University of Reading, Earley Gate; ; The effect of the stratospheric ozone depletion on the thermal and dynamical structure of the middle atmosphere is assessed using two 5-member ensembles of transient GCM simulations; one including linear trends in ozone, the other not, for the 1980–1999 period. Simulated temperatures and observations are in good agreement in terms of mean values, autocorrelations and cross correlations. Annual-mean and seasonal temperature trends have been calculated using the same statistical analysis. Simulations show that ozone trends are responsible for reduced wave activity in the Arctic lower stratosphere in February and March, confirming both the role of dynamics in controlling March temperatures and a recently proposed mechanism whereby Arctic ozone depletion causes the reduction in wave activity entering the lower stratosphere. Changes in wave activity are consistent with an intensification of the polar vortex at the time of ozone depletion and with a weakened Brewer–Dobson circulation: A decrease of the dynamical warming/cooling associated with the descending/ascending branch of the wintertime mean residual circulation at high/low latitudes has been obtained through the analysis of temperature observations (1980–1999). Ozone is responsible of about one third of the decrease of this dynamical cooling at high latitudes. An increase in the residual mean circulation is seen in the observations for the 1965–1980 period.120 24 - PublicationRestrictedSimulations of anthropogenic change in the strength of the Brewer–Dobson circulation(2006)
; ; ; ; ; ; ; ; ; ; ; ; ;Butchart, N.; Met Office, FitzRoy Road, ;Scaife, A. A.; Hadley Centre, Met Office, ;Bourqui, M.; Department of Meteorology, University of Reading, Reading, UK ;de Grandpre, J.; McGill University, Montreal, Canada ;Hare, S. H. E.; Department of Meteorology, University of Reading, Reading, UK ;Kettleborough, J.; Rutherford Laboratory, British Atmospheric Data Centre, ;Langematz, U.; Freie Universita¨ t of Berlin, Berlin, Germany ;Manzini, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Sassi, F.; National Center for Atmospheric Research,Boulder, CO, USA ;Shibata, K.; Meteorological Research Institute, Tsukuba, Japan ;Shindell, D.; NASA-Goddard Institute for Space Studies, New York, USA ;Sigmond, M.; University of Toronto, Toronto, Canada; ; ; ; ; ; ; ; ; ; ; The effect of climate change on the Brewer– Dobson circulation and, in particular, the large-scale seasonal-mean transport between the troposphere and stratosphere is compared in a number of middle atmosphere general circulation models. All the models reproduce the observed upwelling across the tropical tropopause balanced by downwelling in the extra tropics, though the seasonal cycle in upwelling in some models is more semi-annual than annual. All the models also consistently predict an increase in the mass exchange rate in response to growing greenhouse gas concentrations, irrespective of whether or not the model includes interactive ozone chemistry. The mean trend is 11 kt s–1 year–1 or about 2% per decade but varies considerably between models. In all but one of the models the increase in mass exchange occurs throughout the year though, generally, the trend is larger during the boreal winter. On average, more than 60% of the mean mass fluxes can be explained by the EP-flux divergence using the downward control principle. Trends in the annual mean mass fluxes derived from the EP-flux divergence also explain about 60% of the trend in the troposphere-to-stratosphere mass exchange rate when averaged over all the models. Apart from two models the interannual variability in the downward control derived and actual mass fluxes were generally well correlated, for the annual mean.171 26