Evaluating the effects of microphysical complexity in idealised simulations of trade wind cumulus using the Factorial Method 1University of Manchester, School of Earth, Atmospheric and Environmental Sciences, UK
23 Mar 2011
2Met Office, Atmospheric Processes and Parametrization, Exeter, UK
Received: 28 Sep 2010 – Published in Atmos. Chem. Phys. Discuss.: 11 Oct 2010 Abstract. The effect of microphysical and environmental factors on the development of
precipitation in warm idealised cloud is explored using a kinematic 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 cloud 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. At relatively low updraught speeds, the sensitivity of the
bulk schemes was found to depend on the assumptions made
with regards the treatment of droplet activation. It was possible to achieve a much closer agreement between
the single and dual moment bulk schemes by tuning the specified droplet number concentration
in the single moment scheme, suggesting that a diagnostic representation of droplet number may be an
acceptable alternative to the more expensive prognostic option.
However the effect of changes in CCN concentration were found to
produce a relatively stronger effect on precipitation in the bulk schemes compared to the bin scheme;
this is believed to be a consequence of differences in the treatment of drop growth
by collision and coalescence. 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.
Revised: 16 Mar 2011 – Accepted: 17 Mar 2011 – Published: 23 Mar 2011
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., 11, 2729-2746, doi:10.5194/acp-11-2729-2011, 2011.