ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-10-2737-2010 Effects of resolution on the relative importance of numerical and physical horizontal diffusion in atmospheric composition modelling D'Isidoro M. 1 Maurizi A. 1 Tampieri F. 1 CNR-ISAC, via Gobetti 101, 40129 Bologna, Italy 24 03 2010 10 6 2737 2743 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/10/2737/2010/acp-10-2737-2010.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/10/2737/2010/acp-10-2737-2010.pdf

Numerical diffusion induced by advection has a large influence on concentration of substances in atmospheric composition models. At coarse resolution numerical effects dominate, whereas at increasing model resolution a description of physical diffusion is needed. A method to investigate the effects of changing resolution and Courant number is defined here and is applied to the WAF advection scheme (used in BOLCHEM), evidencing a sub-diffusive process. The spread rate from an instantaneous source caused by numerical diffusion is compared to that produced by the physical diffusion necessary to simulate unresolved turbulent motions. The time at which the physical diffusion process overpowers the numerical spread is estimated, and it is shown to reduce as the resolution increases, and to increase with wind velocity.

 References Albertson, J D., Parlange, M B., Kiely, G., and Eichinger, W E.: The average dissipation rate of turbulent kinetic energy in the neutral and unstable atmospheric surface layer, J. Geophys. Res., 102, 13423–13432, 1997. Billet, S J. and Toro, E F.: On WAF-Type Schemes for Multidimensional Hyperbolic Conservation Laws, J. Comput. Phys., 130, 1–24, 1997. Binkowski, F S. and Roselle, S J.: Models-3 Community Multiscale Air Quality (CMAQ) model aerosol component 1. Model description, J. Geophys. Res., 108(D6), 4183, doi:10.1029/2001JD001409, 2003. Bryan, G H., Wyngaard, J C., and Fritsch, J M.: Resolution Requirements for the Simulation of Deep Moist Convection, Mon. Weather Rev., 131, 2394–2416, 2003. Buzzi, A., D'Isidoro, M., and Davolio, S.: A case-study of an orographic cyclone south of the Alps during the MAP SOP, Q. J. Roy. Meteorol. Soc., 129, 1795–1818, 2003. Buzzi, A., Davolio, S., D'Isidoro, M., and Malguzzi, P.: The impact of resolution and of 4-D VAR reanalysis on the simulations of heavy precipitation in MAP cases, Meteorol. Z., 13, 91–97, 2004. Carter, W. P L.: A detailed mechanism for the gas-Phase atmospheric reactions of organic compounds, Atmos. Environ., 27A, 481–518, 1990. Gonçalves, M., Jiménez-Guerrero, P., and Baldasano, J. M.: Contribution of atmospheric processes affecting the dynamics of air pollution in South-Western Europe during a typical summertime photochemical episode, Atmos. Chem. Phys., 9, 849–864, 2009. Hubbard, M E. and Nikiforakis, N.: A Three-Dimensional, Adaptive, Godunov-Type Model for Global Atmospheric Flows, Mon. Weather Rev., 131, 1848–1864, 2003. Huijnen, V., Eskes, H. J., Amstrup, B., Bergstrom, R., Boersma, K. F., Elbern, H., Flemming, J., Foret, G., Friese, E., Gross, A., D'Isidoro, M., Kioutsioukis, I., Maurizi, A., Melas, D., Peuch, V.-H., Poupkou, A., Robertson, L., Sofiev, M., Stein, O., Strunk, A., Valdebenito, A., Zerefos, C., and Zyryanov, D.: Comparison of OMI NO<sub>2</sub> tropospheric columns with an ensemble of global and European regional air quality models, Atmos. Chem. Phys. Discuss., 9, 22271–22330, 2009. Isichenko, M B.: Percolation, statistical topography, and transport in random media, Rev. Mod. Phys., 64, 961–1043, 1992. Jimenez-Guerrero, P., Jorba, O., Baldasano, J M., and Gasso, S.: The use of a modelling system as a tool for air quality management: Annual high-resolution simulations and evaluation, Sci. Total Environ., 390, 323–340, 2008. Kolmogorov, A N.: The local structure of turbulence in incompressible viscous fluid for very large Reynolds numbers, Dokl. Akad. Nauk SSSR, 30, 301, 1941. Mircea, M., D'Isidoro, M., Maurizi, A., Vitali, L., Monforti, F., Zanini, G., and Tampieri, F.: A comprehensive performance evaluation of the air quality model BOLCHEM to reproduce the ozone concentrations over Italy, Atmos. Environ., 42, 1169–1185, 2008. Odman, M T.: A Quantitative Analysis Of Numerical Diffusion Introduced By Advection Algorithms In Air Quality Models, Atmos. Environ., 31, 1933–1940, 1997. Pahlow, M., Parlange, M B., and Porte-Agel, F.: On Monin-Obukhov similarity in the stable atmospheric boundary layer, Bound-Lay. Meteorol., 99, 225–248, 2001. Rood, R R.: Numerical Advection Algorithms and Their Role in Atmospheric Transport and Chemistry Models, Rev. Geophys., 25, 71–100, 1987. Smagorinsky, J.: General circulation experiments with the primitive equations: I. The basic experiment, Mon. Weather Rev., 91, 99–164, 1963. Smolarkiewicz, P K.: A Fully Multidimensional Positive Definite Advection Transport Algorithm with Small Implicit Diffusion, J. Comp. Phys., 54, 325–362, 1984. Tampieri, F. and Maurizi, A.: Evaluation of the dispersion coefficient for numerical simulations of tropospheric transport, Nuovo Cimento C, 30, 395–406, 2007. Wyngaard, J C.: Toward numerical modelling in the "terra incognita", J. Atmos. Sci., 61, 1816–1826, 2004.