Fingerprints of Arctic aerosol-cloud-turbulence interactions in
conserved variable space
Abstract
Late springtime Arctic mixed-phase convective clouds over open water in
the Fram Strait as observed during the recent ACLOUD field campaign are
simulated at turbulence-resolving resolutions. The main research
objective is to gain more insight into the coupling of these cloud
layers to the surface, and into the role played by interactions between
aerosol, hydrometeors and turbulence in this process. A composite case
is constructed based on data collected by two research aircraft on 18
June 2017. The boundary conditions and large-scale forcings are based on
analysis data, while the case is designed to freely equilibrate towards
the observed thermodynamic state. The results are evaluated against a
variety of independent aircraft measurements. The observed cloud macro-
and microphysical structure is well reproduced, consisting of a
stratiform cloud layer in mixed-phase fed by surface-driven convective
transport in predominantly liquid phase. A 3D volume rendering of the
simulated liquid clouds is shown in the Figure. Comparison to noseboom
turbulence measurements suggests that the simulated cloud-surface
coupling is realistic. A joint-pdf analysis of relevant conserved state
variables is then conducted, suggesting that locations where the
mixed-phase cloud layer is strongly coupled to the surface by convective
updrafts act as “hot-spots” for invigorated turbulence, cloud and
aerosol interactions. A mixing-line analysis reveals that the turbulent
mixing is similar to warm convective cloud regimes, but is accompanied
by hydrometeor transitions that are unique for mixed-phase cloud
systems. Distinct fingerprints in the joint-pdf diagrams also explain i)
the typical ring-like shape of ice mass in the outflow cloud deck, ii)
its slightly elevated buoyancy, and iii) an associated local minimum in
CCN. The obtained modeling results advocate the application of this
analysis method also to observational datasets.