QBO-Modulated Mean Meridional Circulation: Insights from MIPAS Tracer-Derived Velocities

This study investigates the Quasi-Biennial Oscillation (QBO)-composite mean meridional circulation during the operational period of the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) from 2002 to 2012. This analysis uses ERA-Interim, JRA-55, and ERA5 reanalysis data alongside MIPAS tracer-derived velocities. Following the SPARC Reanalysis Intercomparison Project (S-RIP) methodology, QBO-W onsets at 20 hPa were deseasonalized and composited, enabling comparisons of zonal-mean vertical and meridional velocities derived from MIPAS tracers with reanalysis data.
Effective transport velocities of the 2-D atmosphere were derived using a direct inversion technique based on MIPAS tracer measurements. This method, detailed in Clarmann and Grabowski (2016), integrates the continuity equation over time to determine mean velocities that replicate observed trace gas distributions. This approach provides observation-based insights into the mean meridional circulation independent of dynamic models. The tracers analyzed include CH4, CO, H2O, and N2O across various atmospheric layers, supplemented by SF6 and CCl4 to reduce uncertainties.
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Distinct QBO patterns were identified in tracer-retrieved velocities, showing favorable agreement with ERA5, ERA-Interim, and JRA-55 reanalysis results. Quantitative comparisons reveal differences, potentially highlighting processes underrepresented in current models or limitations in tracer-based continuity equation inversions.
These findings underscore the value of MIPAS tracer measurements for advancing our understanding and modeling of mean meridional circulation in Earth's atmosphere.

von Clarmann, T. and Grabowski, U.: Direct inversion of circulation and mixing from tracer measurements – Part 1: Method, Atmos. Chem. Phys., 16, 14563–14584, https://doi.org/10.5194/acp-16-14563-2016, 2016.