Chasing ice crystals: interlinking cloud microphysics and dynamics in
cloud seeding plumes with Lagrangian trajectories
Abstract
The ice phase is a major contributor to precipitation formation over
continents due to its efficiency in growing hydrometeors to large enough
sizes for sedimentation. One prominent growth mechanism is the vapor
deposition onto ice crystals. However, its actual growth rates remain
ambiguous. In the CLOUDLAB project, we conducted field experiments in
supercooled clouds with the goal to infer ice crystal growth rates
through local perturbations from cloud seeding. In this study, we
combine the high-resolution model setup of
65\,\unit{m} with Lagrangian trajectories
to achieve a more straightforward comparison to the observations. We
first show that the chosen field experiments can be reproduced in the
model in terms of ice crystal number concentration. Second, we perform a
series of sensitivity studies by perturbing two parameters in the vapor
depositional growth equation. The goal is to understand what change is
needed to achieve an agreement between simulated and observed ice
crystal growth rates since the default model configuration fails to do
so. Increasing the vapor deposition efficiency by a factor of up to 3
yields comparable growth rates to the observations. Last, we try to
quantify the different contributions to the vertical motions within the
seeding plume, such as the large-scale forcing, the underlying
topography, and latent heat release upon ice nucleation and growth. We
show the different factors are superposed with the large-scale forcing
being a dominant factor. The Lagrangian trajectories proved to be
crucial to bridge dynamics and cloud microphysical processes.