This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).
The project will quantify stratosphere-troposphere exchange (STE) using novel transport diagnostics: one-way cross-tropopause flux distributions and path densities with their associated transport rates. This new approach will extend the current knowledge of STE by revealing, with unprecedented detail and precision, a comprehensive picture of transport across the tropopause and through the troposphere and stratosphere. The flux distributions computed with MATCH (Model of Atmospheric Transport and Chemistry), driven by reanalyzed winds, will allow extant disparate estimates of STE fluxes to be validated and reconciled as differently conditioned integrals of the underlying fundamental flux distributions. The path-density diagnostic will quantify the advective-diffusive "conveyor" circulation in the atmosphere, partitioned according to the origins and destination regions of different paths and the origin-to-destination transit time.
This research will make the first substantial use of idealized general circulation models to analyze atmospheric tracers and transport. Analysis of idealized model experiments will determine how different meteorological processes and flow regimes control STE. The computational efficiency of these idealized models will allow the systematic determination of the sensitivities to model parameters so that the robustness of the results can be assessed.
The results of this project will be of value to the wider atmospheric-chemistry community, because the flux-distribution and path-density diagnostics isolate the role of transport in determining atmospheric composition. In particular, the rates and pathways with which different photochemical environments are accessed by both boundary-layer and stratospheric species will be quantified. This will have implications for air quality, by constraining the contribution of stratospheric ozone to boundary-layer air and by quantifying the rates and paths with which boundary-layer air and pollutants are removed to the stratosphere. A baseline climatology of detailed STE transport diagnostics will be provided, from which changes in transport and atmospheric composition caused by future green-house-gas warming can be asssessed. Results will be of value to the observational community, because the geographic distribution of cross-tropopause fluxes, the statistics of deep intrusions and their lifetimes, and the meteorological processes that are conducive to STE will be quantified. This will be useful for planning aircraft and other measurement campaigns.
The computed Green functions and the idealized model configurations will be made available to the community. These tools can be used for a wide variety of investigations on the STE of air and trace species. Research activities will be integrated into teaching and educational outreach. A team of a high-school student, a high-school teacher, and an undergraduate university student from the New-York-City area will participate in the project through the New York City Research Initiative during its annual six-week summer outreach program.
