Atmospheric mixing in a lagrangian framework

Inaccurate representation of mixing in chemistry transport models strongly influence the time evolution of all relevant trace gases and, in particular, the qualitative determination of the stratosphere-troposphere exchange (STE). For this reason, a physics-based numerical representation of mixing is required but remains an uncertain piece for the atmospheric transport models. However, the Lagrangian view of transport offers an alternative to exploit the numerical diffusion for parametrization of the physical mixing rather than to find ways of avoiding this effect. Using the standard version of the Chemical Lagrangian Model of the Stratosphere (CLaMS) with mixing parametrization triggered by strong flow deformations, a remarkable Sudden StratosphericWarming (SSW) case is investigated to reexamine transport, especially mixing, through analyzing the variation of stratospheric composition and of the tracer-tracer correlations. The case study of SSW demonstrates the intensified sub-seasonal variability of polar descent and tropical upwelling, which further motivates the study of the long-term impact of SSWs on the variability of the water vapor in the tropical lower stratosphere based on a CLaMS 35-year run. A sub-seasonal SSW-associated dehydration effect in the tropical lower stratosphere modulated by the two quasi-biennial oscillation (QBO) phases is found. The cooling and drying at the tropical tropopause, as a result of enhanced breaking of planetary waves in the subtropics during SSWs, is more intensive in the easterly QBO phase than in the westerly QBO phase