Aerosols and greenhouse gases at the dynamical tropopause: Lagrangian transport and climatology

The upper troposphere and lower stratosphere (UTLS) serves as the transition region between the two atmospheric layers. Chemical constituents, aerosols, and water are transported in coherent airstreams or mixed from their tropospheric source regions into the UTLS. Therefore, the vertical and geographical distribution of all these constituents in the UTLS strongly depends on the transport or mixing pathways and on their (tropospheric) sources. Furthermore, during the transport constituent concentrations can be modified due to many microphysical and chemical processes. A detailed understanding about the constituent concentrations in the UTLS is needed because of their dynamic-radiative-chemical coupling, which affects atmospheric tracer distributions, the radiative budget and the dynamics of the tropopause.  

We present a 10-year climatology of selected aerosol (dust, sea salt, sulphate), tracer (CO) and greenhouse gas (CO2 and CH4) concentrations at the dynamical tropopause (2-pvu isosurface).  We make use of the Copernicus Atmosphere Monitoring Service reanalysis datasets CAMSRA and CAMS GHG and combine these Eulerian climatologies with a Lagrangian troposphere-to-stratosphere transport (TST) climatology to determine and characterize the pathways from the constituent sources to the UTLS. This way, we analyse anomalies of aerosols and greenhouse gases at the tropopause that arise from the TST, and we compare them to seasonal atmospheric composition climatology.

We show that the TST trajectories that originated from the boundary layer (deep TST) lead to stronger anomalies at the dynamical tropopause. The concentration patterns at the dynamical tropopause for different species depend on the emissions at the surface, the exact dynamical pathway from the surface to the UTLS, and the sinks and sources along the way. For example, we demonstrate that dust concentrations at the dynamical tropopause over Asia are mostly from local dust source regions but they can be enhanced with dust advection from other regions.