| It is still a moot issue about whether, for glaciated cloud-types generally, observed ice
number concentrations can be correctly predicted by a model when its inputs of
aerosol conditions of chemistry and loading are accurately constrained. Partly, the
problem has been a lack of comprehensively observed cases of clouds, in which the
thermodynamics of the atmosphere and cloud properties and some of the aerosol
conditions are observed simultaneously. Equally, ice nucleus species of aerosols are
still incompletely characterised in laboratory studies. In recent years, there was a
new field campaign dedicated to study of ice initiation, namely the "Ice in Clouds
Experiment - Layer-clouds" (ICE-L; Wyoming/Colorado, 2007). The ICE-L campaign
involved observations of aerosol size distributions and aerosol composition with
probes flown on an aircraft, which sampled the coincident properties of mixed-phase
wave-clouds.
In this presentation, a newly improved empirical scheme of heterogeneous ice nucleation,
with dependencies on loadings of black carbon, organics and dust is described. It is shown to
agree with aircraft observations from this ICE-L case of shallow mixed-phase wave-clouds.
Additionally, an aerosol-cloud model using our newly developed scheme of 2-moment bulk
microphysics is described. It includes the empirical scheme and a new treatment of
homogeneous freezing of cloud-liquid, and prognostic treatment of six aerosol species. This
aerosol-cloud model is compared against observations of ice and droplet concentrations for
cases with coincident observations of aerosol and thermodynamic conditions as its
input.
Finally, there may exist some types of clouds where empirical knowledge of ice initiation
is still inadequate (e.g. for overlooked pathways of ice multiplication) for modeling their
glaciation. Such problems are discussed. |