A Lagrangian model diagnosis of stratospheric contributions to tropical midtropospheric air

Using the modeled stratospheric tracer and 3-D back trajectories, we identified that 60% of the observed HOLW air masses contain significant stratospheric influence. We have also examined possible contribution to the HOLW layer from ozone production related to biomass burning emissions. Clear chemical signature of this process is found in∼8% of the HOLW air masses, identified by positive correlations among O3, HCN, and CO.

This analysis provides the first quantitative diagnosis of the contribution from the stratosphere-to-troposphere transport, highlights the importance of mixing in chemical transport, and demonstrates the limitations of pure Lagrangian trajectory calculations in quantifying transport.