Publication Date:
2023-06-21
Description:
Springtime Arctic mixed-phase convection over open water in the Fram Strait as observed during the
recent ACLOUD (Arctic CLoud Observations Using airborne measurements during polar Day) field campaign
is simulated at turbulence-resolving resolutions. The first objective is to assess the skill of large-eddy simulation
(LES) in reproducing the observed mixed-phase convection. The second goal is to then use the model to investigate
how aerosol modulates the way in which turbulent mixing and clouds transform the low-level air mass. The
focus lies on the low-level thermal structure and lapse rate, the heating efficiency of turbulent entrainment, and
the low-level energy budget. A composite case is constructed based on data collected by two research aircraft
on 18 June 2017. Simulations are evaluated against independent datasets, showing that the observed thermodynamic,
cloudy, and turbulent states are well reproduced. Sensitivity tests on cloud condensation nuclei (CCN)
concentration are then performed, covering a broad range between pristine polar and polluted continental values.
We find a significant response in the resolved mixed-phase convection, which is in line with previous LES
studies. An increased CCN substantially enhances the depth of convection and liquid cloud amount, accompanied
by reduced surface precipitation. Initializing with the in situ CCN data yields the best agreement with the
cloud and turbulence observations, a result that prioritizes its measurement during field campaigns for supporting
high-resolution modeling efforts. A deeper analysis reveals that CCN significantly increases the efficiency
of radiatively driven entrainment in warming the boundary layer. The marked strengthening of the thermal inversion
plays a key role in this effect. The low-level heat budget shifts from surface driven to radiatively driven.
This response is accompanied by a substantial reduction in the surface energy budget, featuring a weakened
flow of solar radiation into the ocean. Results are interpreted in the context of air–sea interactions, air mass
transformations, and climate feedbacks at high latitudes.
Repository Name:
EPIC Alfred Wegener Institut
Type:
Article
,
isiRev
Format:
application/pdf