Stratospheric age of air computed with trajectories based on various 3D-Var and 4D-Var data sets

• DOI: 10.5194/acp-5-1-2005
• Publication Date: 2010-04-29T13:42:37Z
• Authors: M. P. Scheele; P. C. Siegmund; P. F. J. Velthoven
• Keywords: Tropopause; Vector autoregression

Abstract. The age of stratospheric air is computed with a trajectory model, using ECMWF ERA-40 3D-Var and operational 4D-Var winds. Analysis as well forecast data are used. In the latter case successive segments put together to get time series wind fields. This done for different segment lengths. sensitivity length assimilation method studied, results compared observations from chemistry transport model that uses same sets. A large number backward trajectories started in stratosphere, fraction these has passed tropopause computed. First, ten sets 50-day starting tropical lower stratosphere show this region cross-tropopause decreases increasing length. Next, three selected (3D-Var 24-h 72-h segments, analyses) 5-year start all over globe at an altitude 20km. For ages extratropics smaller than observation-based age. they closest values, but still 0.5-1.5 year too small. Compared difference between sets,