Commentary on cloud modelling and the mass accommodation coefficient of water A. Laaksonen1, T. Vesala2, M. Kulmala2, P. M. Winkler3, and P. E. Wagner3 1Department of Applied Physics, University of Kuopio, P.O. Box 1627, FIN-70211 Kuopio, Finland 2Department of Physical Sciences, University of Helsinki, P.O. Box 64, FIN-00014 Helsinki, Finland 3Institut für Experimentalphysik, Universität Wien, Boltzmanngasse 5, A-1090 Wien, Austria
Abstract. The mass accommodation coefficient of water is a quantity for
which different experimental techniques have yielded conflicting values
in the range 0.04-1. From the viewpoint of cloud modelling, this is an unfortunate
situation, since the value of the mass accommodation coefficient
affects the model results, e.g. the number concentration of activated
cloud droplets. In this commentary we note that in cloud modelling, the primary quantity
of interest is the droplet growth rate rather than the mass accommodation coefficient, and
that experimental investigations of droplet growth rates provide more direct verification
of cloud models than do measurements of the mass
Furthermore, we argue that the droplet growth rates calculated in cloud model studies are
consistent with experimental results obtained so far only if a mass accommodation
coefficient of unity is applied.
Citation: Laaksonen, A., Vesala, T., Kulmala, M., Winkler, P. M., and Wagner, P. E.: Commentary on cloud modelling and the mass accommodation coefficient of water, Atmos. Chem. Phys., 5, 461-464, doi:10.5194/acp-5-461-2005, 2005.