Influence of entrainment of CCN on microphysical properties of warm cumulus Institute for Marine and Atmospheric Research Utrecht (IMAU), Utrecht University, Utrecht, The Netherlands
Received: 03 February 2009 – Published in Atmos. Chem. Phys. Discuss.: 02 April 2009 Abstract. We use a 1-D cloud model with explicit microphysics and a binned
representation of the aerosol size distribution to investigate the influence
of entrainment of cloud condensation nuclei (CCN) on the microphysical
development of warm cumulus clouds. For a more realistic representation of
cloud drop spectral width, the model separates droplets that grow on aerosol
that is initially present in the cloud from droplets growing on entrained
aerosol. Model results are compared with observations of trade wind cumulus
microphysics from the Rain in Cumulus over the Ocean experiment (RICO,
2004–2005). The results indicate that CCN are entrained throughout the
entire cloud depth, and inside the cloud part of these may be activated.
Compared to a simulation where entrainment of ambient CCN is neglected this
leads to higher cloud droplet number concentrations (CDNC) and a continuous
presence of droplets in the range smaller than ~5 μm that is
consistent with the observations. Cloud dynamics are sensitive to the
entrainment parameter as well as to the applied initial vertical velocity, as
expressed by the liquid water content and cloud top height. However,
simulated cloud drop spectra remain relatively unaffected for the specific
conditions during RICO.
Revised: 09 July 2009 – Accepted: 14 July 2009 – Published: 20 August 2009
Citation: Derksen, J. W. B., Roelofs, G.-J. H., and Röckmann, T.: Influence of entrainment of CCN on microphysical properties of warm cumulus, Atmos. Chem. Phys., 9, 6005-6015, doi:10.5194/acp-9-6005-2009, 2009.