Sonia Kreidenweis (PI)
Colorado State University
sonia@chem.atmos.colostate.edu
Modeling Studies of Aerosol-Cold Cloud Interactions
It is proposed to develop two variations of a parcel-type model of aerosol-cloud
interactions to be used to study drop formation at cold temperatures,
homogeneous freezing, heterogeneous freezing, and the competition for
water vapor between condensation, freezing, and crystal growth. Building
on our prior modeling work for aerosol-warm cloud interactions, the ambient
environment can be represented either as an adiabatic parcel or the ambient
conditions can be specified along a trajectory diagnosed from a dynamical
simulation. This permits application of the model to a variety of dynamical
regimes. The aerosol and its interaction with water vapor are modeled
in two ways. In the first, the particle size evolution is treated in
a Lagrangian framework, minimizing diffusional errors, easily accommodating
a variety of aerosol types and size distributions, and permitting variable
resolution in particle size-space. In the second, we employ a more conventional
bin-microphysical representation, which permits calculation of particle-particle
interactions such as collision-coalescence. There is a need in the community
for such models for several reasons. First, the limited numerical studies
appearing in the literature have usually assumed a simplified description
of the aerosol, such as a single composition or a lognormal size distribution.
A few interesting parametric studies have been presented, again using
conceptualized aerosol inputs which should be refined. We now have a
wealth of in situ aerosol data, due in large part to NASA-sponsored field
missions, that can be used to develop more realistic inputs and improved
representation of the ice initiation process, and new models are needed
to accommodate such data and more fully explore parameter space. Second,
only recently have in-situ, airborne measurements of homogeneous freezing
nucleation of liquid aerosols and ice formation by heterogeneous ice
nuclei been available. Our group has been in the forefront of producing
these data on ice nucleation and we are in a unique position to integrate
them into improved representations of the ice formation process and its
link to aerosol abundance and characteristics.
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