Atmos. Chem. Phys. Discuss., 11, 9607-9633, 2011
© Author(s) 2011. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Cloud-base vertical velocity statistics: a comparison between an atmospheric mesoscale model and remote sensing observations
J. Tonttila1,3, E. J. O'Connor1,2, S. Niemelä1, P. Räisänen1, and H. Järvinen1
1Finnish Meteorological Institute, P.O. Box 503, 00101 Helsinki, Finland
2Meteorology Department, University of Reading, Reading, UK
3Division of Atmospheric Sciences, Department of Physics, University of Helsinki, Helsinki, Finland

Abstract. The statistics of cloud-base vertical velocity simulated by the non-hydrostatic mesoscale model AROME are compared with Cloudnet remote sensing observations at two locations: the ARM SGP site in Central Oklahoma, and the DWD observatory at Lindenberg, Germany. The results show that, as expected, AROME significantly underestimates the variability of vertical velocity at cloud-base compared to observations at their nominal resolution; the standard deviation of vertical velocity in the model is typically 4–6 times smaller than observed, and even more during the winter at Lindenberg. Averaging the observations to the horizontal scale corresponding to the physical grid spacing of AROME (2.5 km) explains 70–80% of the underestimation by the model. Further averaging of the observations in the horizontal is required to match the model values for the standard deviation in vertical velocity. This indicates an effective horizontal resolution for the AROME model of at least 4 times the physically-defined grid spacing. The results illustrate the need for special treatment of sub-grid scale variability of vertical velocities in kilometer-scale atmospheric models, if processes such as aerosol-cloud interactions are to be included in the future.

Citation: Tonttila, J., O'Connor, E. J., Niemelä, S., Räisänen, P., and Järvinen, H.: Cloud-base vertical velocity statistics: a comparison between an atmospheric mesoscale model and remote sensing observations, Atmos. Chem. Phys. Discuss., 11, 9607-9633, doi:10.5194/acpd-11-9607-2011, 2011.
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