Dear Team,
On Friday, Sep 20 at 10 am, we will host Tim Lüttmer from
Johannes Gutenberg University of Mainz for our group's seminar.
Title: Ice Formation Pathways In Warm Conveyor Belts
Abstract below. Room 7, D-10.
Best,
Sylwester
Abstract:
Warm Conveyor Belts (WCB) lead to formation of horizontally wide spread
Cirrus clouds in the upper troposphere. However, the contribution of
different ice formation processes and the resulting micro- and
macrophysical properties of the Cirrus ,e.g., their radiative effects
are still poorly understood. We want to especially address the research
question of in-situ vs. liquid origin ice formation.
Common microphysics bulk schemes only consider a single ice class which
includes sources from multiple formation mechanisms. We developed and
implemented a two-moment microphysics scheme in the atmosphere model
ICON that distinguishes between different ice modes of origin including
homogeneous nucleation, deposition freezing, immersion freezing,
homogeneous freezing of water droplets and secondary ice production.
Each ice mode is described by its own size distribution, prognostic
moments and unique formation mechanism while still interacting with all
other ice modes and microphysical classes like cloud droplets, rain and
rimed cloud particles.
Using this microphysics scheme we can directly determine the
contribution of the various icef ormation mechanisms to the total ice
content. The distinction between ice modes also allows a novel
classification of cirrus origin based on their mircophysical composition
without needing to consider the history of the cloud. Using this
method we investigate the competition of in-situ and liquid origin
cirrus as well as homogeneous and heterogeneous ice nucleation with
regards to environmental conditions and choice of parametrizations.
We performed sensitivity simulations for choice of various heterogeneous
nucleation parametrizations and for an ensemble of perturbations in
the number concentrations of ice nucleating particles. Additionally we
simulated 10 WCB cases to investigate the impact of different
environmental conditions on the ice formation pathways. Key findings are
(1) Sedimentation significantly affects the in-situ vs liquid origin
classification,
(2) Characteristic properties of in-situ and liquid origin cirrus are
sensitive to WCB ascent times,
(3) Choice of parametrization strongly affects the competition between
homogeneous and heterogeneous nucleation, but not between in-situ and
liquid ice formation pathways.
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Environmental Physics Group, AGH University of Kraków, Poland
sylwester.arabas(a)agh.edu.pl | +48502254779 | https://slayoo.github.io/
