Abstract
We generated a large number (105’000) of aggregates composed of various
monomer types and sizes using an aggregation model. Combined with
hydrodynamic theory, we derived ice particle properties such as mass,
projected area, and terminal velocity as a function of monomer number
and size. This particle ensemble allows us to study the relation of
particle properties with a high level of detail which is often not
provided by in-situ measurements. The ice particle properties change
rather smoothly with monomer number. We find very little differences in
all particle properties between monomers and aggregates at sizes below 1
mm which is in contrast to many microphysics schemes. The impact of the
monomer type on the particle properties decreases with increasing
monomer number. Whether e.g., the terminal velocity of an aggregate is
larger or smaller than an equal-size monomer, depends mostly on the
monomer type. We fitted commonly used power laws as well as Atlas-type
relations, which represent the saturation of the terminal velocity at
larger sizes (terminal velocity asymptotically approaching a limiting
value), to the dataset and tested the impact of incorporating different
levels of complexity with idealized simulations using a 1D Lagrangian
super-particle model. These simulations indicate that it is sufficient
to represent the monomer number dependency of ice particle properties
with only two categories (monomers and aggregates). The incorporation of
the saturation velocity at larger sizes is found to be important to
avoid an overestimation of self-aggregation of larger snowflakes.