ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-12-525-2012 Microphysical controls on the stratocumulus topped boundary-layer structure during VOCALS-REx Boutle I. A. 1 Abel S. J. 1 Met Office, Exeter, UK 06 01 2012 12 1 525 557 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-discuss.net/12/525/2012/acpd-12-525-2012.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/12/525/2012/acpd-12-525-2012.pdf

Simulations at a range of resolutions are compared to observations from the South-East Pacific taken during VOCALS-REx. It is found that horizontal resolution makes little difference to the bulk properties of the simulated cloud and drizzle, but the highest resolution simulation is able to realistically represent mesoscale features in the cloud field. We focus on the highest resolution simulation and demonstrate that a poor representation of the cloud microphysics results in excessive drizzle production. This promotes persistent drizzle induced decoupling of the boundary layer, giving a poor representation of the observed diurnal cycle of stratocumulus. Two simple changes to the microphysics scheme are implemented, resulting in a more realistic simulation of boundary-layer diurnal decoupling, and improvements to the cloud liquid water path and surface drizzle rate.

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