Sensitivity of tracer transport to model resolution, forcing data and tracer lifetime in the general circulation model ECHAM5

By A. Aghedo, S. Rast, M. G. Schultz. 2008

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The transport of tracers in the general circulation model ECHAM5 is analysed using 9 independent idealized tracers with constant lifetimes released in di ff erent altitude regions of the atmosphere. The source regions were split into the tropics, Northern and Southern Hemisphere. The dependency of tracer transport on model resolution is 5 tested in the resolutions T21L19, T42L19, T42L31, T63L31 and T106L31, by employ-ing tracers with a globally uniform lifetime of 5 months. Each of the experiments uses prescribed sea surface temperatures and sea ice fields of the 1990s. The influence of meteorology and tracer lifetimes were tested by performing additional experiments in the T63L31 resolution, by nudging ECHAM5 towards the European Centre for Medium 10 Range Weather Forecast 40 years re-analysis data (ERA40), and by using tracer lifetimes of 0.5 and 50 months, respectively. The transport of tracers is faster in the finer resolution models and is mostly dependent on the number of vertical levels. We found a decrease in the inter-hemispheric transport of tracers with source region at the surface or the tropopause in the coarse resolution models due to increasing recirculation 15 within the source region and vertical mixing. However, a coarse model resolution leads to enhanced inter-hemispheric transport in the stratosphere. The use of ERA40 data only slightly a ff ects the inter-hemispheric transport of surface and tropopause tracers, whereas it increases the inter-hemispheric and vertical transport in the stratosphere by up to 100% and by a factor of 2.5, respectively. The inter-hemispheric transport time 20 was deduced from simulations with tracers of infinite lifetime and source regions at the surface in the Northern and Southern Hemisphere. Again, the transport was found to

Subfields: Atmospheric Science, Global and Planetary Change

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