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Optimizing transport properties in TM5 using SF6

Veen, Emma van der (2013) Optimizing transport properties in TM5 using SF6.

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Abstract:Increasingly, global chemistry transport models are used to estimate sources and sinks (fluxes) of CO2 with a data-assimilation (DA) approach. A recent transport model intercomparison study shows that vertical mixing, implemented differently in the various transport models, strongly influences the estimated carbon fluxes. Therefore, improving vertical (and horizontal) transport in such models is required. In this study, we focus on horizontal transport in the global chemistry Transport Model, version 5 (TM5) with simulations of the anthropogenic compound SF6. As many other transport models, TM5 simulates too slow interhemispheric mixing of trace gasses, and hence overestimates the observed concentration gradient between the Northern and Southern Hemispheres. To tackle the problem, we firstly examine the performance of a DA system, namely the Ensemble Kalman Filter, in estimating uxes and transport properties in a 1-D advection-diffusion model. Hereafter, we improve transport in TM5 by tuning horizontal difusivity of the numerical scheme. Lastly, we aim to capture an actual process that represents (extra) horizontal transport, and parameterize it as a diffuse process in strong convective areas. We demonstrate an optimal value for the transport parameter by optimization with the Carbon Tracker Data Assimilation System (CTDAS). Both the numerical adjustment and the parameterization improve interhemispheric mixing in TM5, as we also validate with independent aircraft data.
Item Type:Essay (Master)
Faculty:EEMCS: Electrical Engineering, Mathematics and Computer Science
Subject:31 mathematics
Programme:Applied Mathematics MSc (60348)
Link to this item:http://purl.utwente.nl/essays/65459
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