Abstract. The equivalent length, a measure for mixing strength in the atmosphere, in meridional direction in the current application, is used here to investigate the causes of the atmospheric chemistry model (TM3, TM5-4DVAR and LMDz-PYVAR) biases in the stratosphere. Compared to measurements, we find that the modeled surf zone (a strongly stirred region caused by planetary wave breaking in mid-latitude stratosphere in the winter hemisphere), especially in the southern hemisphere, is not strong enough. We assume that this is due to an underestimation of the planetary wave breaking magnitude in the models. Consequently, the region with meridional uniform stratospheric CH4 concentrations has smaller latitudinal coverages in the models than the measurements, especially in the southern hemisphere between June and September. During the southern winter, a region with both vertically and horizontally well mixed CH4 concentrations occur between 450 and 850 K (~ 18 and 30 km) in surf zone latitudes. Such a region is absent in the models, and underestimations of CH4 concentrations within it are visible in comparisons with measured CH4 profiles. The modeled polar vortex breaks too fast and during the vortex period CH4 concentration differences across its barrier are underestimated compared to the measurements.
How to cite. Wang, Z., Warneke, T., Dils, B., Notholt, J., and Saunois, M.: Diagnosing CH4 models using the equivalent length in the
stratosphere, Atmos. Chem. Phys. Discuss. [preprint], https://doi.org/10.5194/acp-2017-435, 2017.
Received: 09 May 2017 – Discussion started: 22 May 2017
It is important to know to what extent the chemistry transport model represents tracer transport in the atmosphere correctly. In this study we evaluate performances of three models in the stratosphere in describing mixing processes there. The results reveal that deficiencies exist in representing mixing processes in mid-latitudes of southern stratosphere. Another related problem of the models is in representing tracer gradients across transport barrier.
It is important to know to what extent the chemistry transport model represents tracer transport...