Articles | Volume 18, issue 19
Atmos. Chem. Phys., 18, 14253–14269, 2018
https://doi.org/10.5194/acp-18-14253-2018

Special issue: Results of the project "Dynamics–aerosol–chemistry–cloud...

Atmos. Chem. Phys., 18, 14253–14269, 2018
https://doi.org/10.5194/acp-18-14253-2018

Research article 09 Oct 2018

Research article | 09 Oct 2018

The role of droplet sedimentation in the evolution of low-level clouds over southern West Africa

Christopher Dearden1,a, Adrian Hill2, Hugh Coe1, and Tom Choularton1 Christopher Dearden et al.
  • 1Centre for Atmospheric Science, School of Earth and Environmental Science, University of Manchester, Manchester, UK
  • 2Met Office, Exeter, UK
  • anow at: Centre of Excellence for Modelling the Atmosphere and Climate, School of Earth and Environment, University of Leeds, Leeds, UK

Abstract. Large-eddy simulations are performed to investigate the influence of cloud microphysics on the evolution of low-level clouds that form over southern West Africa during the monsoon season. We find that, even in clouds that are not precipitating, the size of cloud droplets has a non-negligible effect on liquid water path. This is explained through the effects of droplet sedimentation, which acts to remove liquid water from the entrainment zone close to cloud top, increasing the liquid water path. Sedimentation also produces a more heterogeneous cloud structure and lowers cloud base height. Our results imply that an appropriate parameterization of the effects of sedimentation is required to improve the representation of the diurnal cycle of the atmospheric boundary layer over southern West Africa in large-scale models.

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Short summary
We perform computer simulations of the life cycle of low-lying clouds over southern West Africa during the monsoon season. Such clouds tend not to produce much precipitation, but they do affect the regional climate by modifying the amount of sunlight reaching the surface. The aim of this work is to understand the factors that influence the growth and break-up of these clouds. We show that the number of water droplets contained within the clouds affects how quickly they dissipate.
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