Trends in stratospheric transport pathways and impacts on (surface) climate (TRIP)

Felix Ploeger, Charlotte Hoppe, und Rolf Müller
Research Center Juelich, Institute for Energy- and Climate Research, Stratosphere (IEK-7)

Variability and trends of transport pathways affect the trace gas composition of the stratosphere which, in turn, crucially impacts radiative forcing and climate change.  This proposal aims at developing novel diagnostic tools for improving our understanding of transport pathways in the stratosphere in a changing climate, particularly their trends on seasonal to decadal time scales and the impact of these trends on trace gas composition and on surface temperatures. Based on the Lagrangian chemistry transport model CLaMS, integrated into the comprehensive Earth system model EMAC, a new method for calculating the age spectrum of stratospheric air for non-stationary (time dependent) atmospheric flow will be developed. Considering the time dependent age spectrum, the probability distribution of transit times of air from the tropical tropopause, goes far beyond current research where mainly the mean age is considered. The method will be validated against age spectra from pulse experiments and against mean age estimates from observations. In particular, model based age of air calculations will be compared to observations, in close collaboration with the ROMIC-project BDCHANGE (GU Frankfurt, KIT Karlsruhe). The combination of age spectra, trace gas simulations and observations will gain unprecedented insights into the relative strengths of different transport pathways between the tropical and the extratropical stratosphere and into long-term circulation trends. Furthermore, effects on the temperature structure and feedbacks on the circulation via changes in transport will be studied within the CLaMS-EMAC model. The proposed age spectrum diagnostic will be of outstanding relevance also for climate model transport evaluation as it enables to detect deficiencies in model transport which are