Atmos. Chem. Phys. Discuss., 10, 23497-23537, 2010
© Author(s) 2010. This work is distributed
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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.
Evaluating the effects of microphysical complexity in idealised simulations of trade wind cumulus using the Factorial Method
C. Dearden1, P. J. Connolly1, T. W. Choularton1, and P. R. Field2
1University of Manchester, School of Earth, Atmospheric and Environmental Sciences, UK
2Met Office, Atmospheric Processes and Parametrization, Exeter, UK

Abstract. The effect of microphysical and environmental factors on the development of precipitation in warm idealised clouds are explored using an idealised process modelling framework. A simple one-dimensional column model is used to drive a suite of microphysics schemes including a flexible multi-moment bulk scheme (including both single and dual moment liquid water) and a state-of-the-art bin-resolved scheme with explicit treatments of liquid and aerosol. The Factorial Method is employed to quantify and compare the sensitivities of each scheme under a set of controlled conditions, in order to isolate the effect of additional microphysical complexity in terms of the impact on surface precipitation. For the schemes considered, and in the absence of entrainment, surface precipitation totals were found to depend increasingly on the meteorological conditions as the level of microphysical complexity is increased. The dual-moment liquid bulk scheme was shown to provide the best agreement with the bin scheme when the cloud base updraught speeds are relatively weak. At higher updraughts, all schemes show that the sensitivity to the magnitude of vertical velocity reduces dramatically, and any subsequent change in precipitation is governed almost entirely by the change in aerosol concentration. However the effect of changes in temperature were found to be underestimated in the bulk schemes compared to the bin scheme; this can be accounted for through differences in the depletion of rain below cloud base by evaporation. Collectively, these results demonstrate the usefulness of the Factorial Method as a model development tool for quantitatively comparing and contrasting the behaviour of microphysics schemes of differing levels of complexity within a specified parameter space.

Citation: Dearden, C., Connolly, P. J., Choularton, T. W., and Field, P. R.: Evaluating the effects of microphysical complexity in idealised simulations of trade wind cumulus using the Factorial Method, Atmos. Chem. Phys. Discuss., 10, 23497-23537, doi:10.5194/acpd-10-23497-2010, 2010.
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