Publications (4)0 Total impact
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Article: Trace gas transport in the 1999/2000 Arctic winter: comparison of nudged GCM runs with observations
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ABSTRACT: We have compared satellite and balloon observations of methane (CH<sub>4</sub>) and hydrogen fluoride (HF) during the Arctic winter 1999/2000 with results from the MA-ECHAM4 middle atmospheric general circulation model (GCM). For this purpose, the meteorology in the model was nudged towards ECMWF analyses. This nudging technique is shown to work well for this middle atmospheric model, and offers good opportunities for the simulation of chemistry and transport processes. However, caution must be used inside the polar vortex, particularly late in the winter. The current study focuses on transport of HF and CH<sub>4</sub>, initialized with satellite measurements from the HALOE instrument aboard the UARS satellite. We have compared the model results with HALOE data and balloon measurements throughout the winter, and analyzed the uncertainties associated with tracer initialization, boundary conditions and the passive tracer assumption. This comparison shows that the model represents some aspects of the Arctic vortex well, including relatively small-scale features. However, while profiles outside the vortex match observations well, the model underestimates HF and overestimates CH<sub>4</sub> concentrations inside the vortex, particularly in the middle stratosphere. This problem is also evident in a comparison of vortex descent rates based upon vortex average tracer profiles from MA-ECHAM4, and various observations. This could be due to an underestimate of diabatic subsidence in the model, or due to too much mixing between vortex and non-vortex air.Atmospheric Chemistry and Physics. 01/2004; -
Article: The impact of model grid zooming on tracer transport in the 1999/2000 Arctic polar vortex
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ABSTRACT: We have used a 3D chemistry transport model to evaluate the transport of HF and CH<sub>4</sub> in the stratosphere during the Arctic winter of 1999/2000. Several model experiments were carried out with the use of a zoom algorithm to investigate the effect of different horizontal resolutions. Balloon-borne and satellite-borne observations of HF and CH<sub>4</sub> were used to test the model. In addition, air mass descent rates within the polar vortex were calculated and compared to observations. Outside the vortex the model results agree well with the observations, but inside the vortex the model underestimates the observed vertical gradient in HF and CH<sub>4</sub>, even when the highest available resolution (1º x 1º) is applied. The calculated diabatic descent rates agree with observations above potential temperature levels of 450 K. These model results suggest that too strong mixing through the vortex edge could be a plausible cause for the model discrepancies, associated with the calculated mass fluxes, although other reasons are also discussed. Based on our model experiments we conclude that a global 6º x 9º resolution is too coarse to represent the polar vortex, whereas the higher resolutions, 3º x 2º and 1º x 1º, yield similar results, even with a 6º x 9º resolution in the tropical region.Atmospheric Chemistry and Physics. 01/2003; -
Article: Trace gas transport in the 1999/2000 Arctic winter: comparison of nudged GCM runs with observations
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Article: Trace gas transport in the 1999/2000 Arctic winter; comparison of nudged GCM runs with observations
