Modeling microphysical effects of entrainment in clouds observed during EUCAARI-IMPACT field campaign 1Institute of Geophysics, Faculty of Physics, University of Warsaw, Warsaw, Poland
27 Aug 2013
2National Center for Atmospheric Research, Boulder, Colorado, USA
Received: 13 December 2012 – Published in Atmos. Chem. Phys. Discuss.: 15 January 2013 Abstract. This paper discusses aircraft observations and large-eddy simulation
(LES) modeling of 15 May 2008, North Sea boundary-layer clouds
from the EUCAARI-IMPACT field campaign. These clouds are advected
from the northeast by the prevailing lower-tropospheric winds and
featured stratocumulus-over-cumulus cloud formations. An almost-solid
stratocumulus deck in the upper part of the relatively deep, weakly
decoupled marine boundary layer overlays a field of small cumuli.
The two cloud formations have distinct microphysical characteristics
that are in general agreement with numerous past observations of
strongly diluted shallow cumuli on one hand and solid marine
stratocumulus on the other.
Revised: 15 July 2013 – Accepted: 19 July 2013 – Published: 27 August 2013
Based on the available observations, a LES model setup is developed
and applied in simulations using a novel LES model. The model
features a double-moment warm-rain bulk microphysics scheme combined
with a sophisticated subgrid-scale scheme allowing local prediction
of the homogeneity of the subgrid-scale turbulent mixing. The
homogeneity depends on the characteristic time scales for the droplet
evaporation and for the turbulent homogenization. In the model,
these scales are derived locally based on the subgrid-scale turbulent
kinetic energy, spatial scale of cloudy filaments, mean cloud droplet
radius, and humidity of the cloud-free air entrained into a cloud,
all predicted by the LES model. The model reproduces contrasting
macrophysical and microphysical characteristics of the cumulus and
stratocumulus cloud layers. Simulated subgrid-scale turbulent
mixing within the cumulus layer and near the stratocumulus top is
on average quite inhomogeneous, but varies significantly depending
on the local conditions.
Citation: Jarecka, D., Pawlowska, H., Grabowski, W. W., and Wyszogrodzki, A. A.: Modeling microphysical effects of entrainment in clouds observed during EUCAARI-IMPACT field campaign, Atmos. Chem. Phys., 13, 8489-8503, doi:10.5194/acp-13-8489-2013, 2013.