Trace gas transport in the 1999/2000 Arctic winter: comparison of nudged GCM runs with observations M. K. van Aalst1, M. M. P. van den Broek2, A. Bregman3, C. Brühl4, B. Steil4, G. C. Toon5, S. Garcelon6, G. M. Hansford6, R. L. Jones6, T. D. Gardiner7, G. J. Roelofs1, J. Lelieveld4, and P.J. Crutzen4 1Institute for Marine and Atmospheric Research (IMAU), Utrecht, The Netherlands 2Space Research Organisation of the Netherlands (SRON), Utrecht, The Netherlands 3Royal Netherlands Meteorological Institute (KNMI), De Bilt, The Netherlands 4Max Planck Institut für Chemie (MPI), Mainz, Germany 5Jet Propulsion Laboratory (JPL), Pasadena, CA, USA 6Cambridge University, Cambridge, UK 7National Physical Laboratory (NPL), Teddington, UK
Abstract. We have compared satellite and balloon observations of methane
(CH4) 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
CH4, 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 CH4 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.
Citation: van Aalst, M. K., van den Broek, M. M. P., Bregman, A., Brühl, C., Steil, B., Toon, G. C., Garcelon, S., Hansford, G. M., Jones, R. L., Gardiner, T. D., Roelofs, G. J., Lelieveld, J., and Crutzen, P.J.: Trace gas transport in the 1999/2000 Arctic winter: comparison of nudged GCM runs with observations, Atmos. Chem. Phys., 4, 81-93, doi:10.5194/acp-4-81-2004, 2004.