QUANTifying stratospheric circulation Impacts on Tropospheric Emission Estimates (QUANTITEE)

• Applicant: Professor Dr. Felix Plöger
• Subject Area: Atmospheric Science
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 462476233

Recent studies have provided evidence that emissions of one of the most important chlorofluorocarbons (CFCs), i.e., CFC-11, have started to increase again since around 2012, implying a potentially severe threat to the stratospheric ozone layer. However, estimates of CFC emissions are prone to large uncertainty caused by changes in the stratospheric circulation which, in turn, are insufficiently constrained in current atmospheric models and reanalyses. Moreover, the methodologies to constrain the representation of stratospheric circulation patterns and variations in stratospheric models with observations are limited.The goal of this project is to enhance the understanding of the impacts of inter-annual to decadal variability in stratospheric transport on tropospheric variations of long-lived trace gases, with focus on CFCs. For this reason, we will evaluate and further improve novel methods for deducing stratospheric age of air spectra, the transit time distribution through the stratosphere which is an advantageous diagnostic for stratospheric transport. In a first step, the method evaluation will be carried out in a model environment. Three different methods for calculating age spectra from mixing ratios of chemical species will be compared, based on (i) an inverse Gaussian parameterization of the spectrum, (ii) an improved parameterization, and (iii) a direct inversion approach. A careful “proof of concept” will be carried out for all three methods by comparison to model age spectra calculated with the (exact) pulse method in the Chemical Lagrangian Model of the Stratosphere (CLaMS). In a second step, the methods will be applied to high-resolution in-situ trace gas measurements on air samples collected in the stratosphere, both with the more conventional aircraft samplers and a new technique based on AirCores. Hence, age spectra will be calculated from a combination of new age spectra simulation techniques and novel observations, providing unprecedented constraints on variations of stratospheric transport. A comparison to model age spectra from simulations driven by different meteorological reanalyses, including newest (ERA5) and older products (ERA-Interim, MERRA-2, JRA-55), will allow assessing the reliability of the representation of stratospheric transport variations. Finally, transport variability (e.g., related to the QBO) will be analyzed and the effects on trace gas composition in the lower stratosphere and on tropospheric trends will be quantified. The improved methods to infer tropospheric budgets will be a legacy tool for the scientific community to better constrain future emissions of many long-lived ozone-depleting substances and greenhouse gases.

• DFG Programme: Research Grants
• International Connection: France
• Co-Investigator: Dr. Johannes C. Laube
• Cooperation Partner: Dr. Aurelien Podglajen