ALBERT

Description: We present the first complete budget of the interannual variability in Arctic springtime ozone taking into account anthropogenic chemical and natural dynamical processes. For the winters 1991/1992 to 2003/2004 the Arctic chemical ozone loss is available from observations. This work investigates the dynamical supply of ozone to the Arctic polar vortex due to mean transport processes for the same winters. The ozone supply is quantified in a vortex-averaged framework using estimates of diabatic descent over winter. We find that the interannual variability of both dynamical ozone supply and chemical ozone loss contribute, in equal shares, to the variability of the total ozone change. Moreover, together they explain nearly all of the interannual variability of Arctic springtime column ozone. Variability in planetary wave activity, characterized by the Eliassen-Palm flux at 100 hPa, contributes significantly to the variability of ozone supply, chemical ozone loss and total springtime ozone.

Description: Interest in stratospheric aerosol and its role in climate have increased over the last decade due to the observed increase in stratospheric aerosol since 2000 and the potential for changes in the sulfur cycle induced by climate change. This review provides an overview about the advances in stratospheric aerosol research since the last comprehensive assessment of stratospheric aerosol was published in 2006. A crucial development since 2006 is the substantial improvement in the agreement between in situ and space-based inferences of stratospheric aerosol properties during volcanically quiescent periods. Furthermore, new measurement systems and techniques, both in situ and space based, have been developed for measuring physical aerosol properties with greater accuracy and for characterizing aerosol composition. However, these changes induce challenges to constructing a long-term stratospheric aerosol climatology. Currently, changes in stratospheric aerosol levels less than 20% cannot be confidently quantified. The volcanic signals tend to mask any nonvolcanically driven change, making them difficult to understand. While the role of carbonyl sulfide as a substantial and relatively constant source of stratospheric sulfur has been confirmed by new observations and model simulations, large uncertainties remain with respect to the contribution from anthropogenic sulfur dioxide emissions. New evidence has been provided that stratospheric aerosol can also contain small amounts of nonsulfate matter such as black carbon and organics. Chemistry-climate models have substantially increased in quantity and sophistication. In many models the implementation of stratospheric aerosol processes is coupled to radiation and/or stratospheric chemistry modules to account for relevant feedback processes

Description: A multiyear time series of the vortex-averaged diabatic descent for 47 Arctic winters from 1957/1958 until 2003/2004 is presented. The climatology of diabatic descent is based on trajectory calculations coupled with diabatic heating rate calculations carried out in the polar lower stratosphere of the Northern Hemisphere winters. We demonstrate the improved performance of the approach based on diabatic heating rates compared to the approach based on vertical winds from meteorological analysis. The time series of the vortex-averaged diabatic descent gives a detailed picture of intensity and altitude dependence of the stratospheric vertical transport processes during the Arctic winter. In addition to the overall vortex-averaged diabatic descent, the spatial structure of the descent is analyzed for two different Arctic winters. We demonstrate for this case study that not only the intensity but also the zonal structure of the diabatic descent depends on the meteorological conditions in the polar vortex. The climatology is characterized by very pronounced interannual variability which is linked to the variability of temperature anomalies and to the variability of Eliassen-Palm (EP)-flux anomalies, wherein strong planetary wave activity leads to strong diabatic descent and vice versa. The correlation between EP-flux and descent shows that tropospheric dynamics have a strong influence on the strength of the polar branch of the residual circulation by means of the atmospheric wave activity.