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Life Cycle of Numerically Simulated Shallow Cumulus Clouds. Part I: Transport
M. Zhao and P. H. Austin
Journal of the Atmospheric Sciences , 2005, 62, 1269-1290.
Abstract
This paper is the first in a two-part series in which the life cycles
of numerically simulated shallow cumulus clouds are systematically
examined. The life cycle data for six clouds with a range of
cloud-top heights are isolated from an equilibrium trade cumulus field
generated by a large eddy simulation (LES) with a uniform resolution of
25 m. A passive subcloud tracer is used to partition the cloud
life-cycle transport into saturated and unsaturated components; the
tracer shows that on average cloud convection occurs in a region with
time-integrated volume roughly 2-3 times that of the liquid
water-containing volume. All six clouds exhibit qualitatively similar
vertical mass flux profiles, with net downward mass transport at upper
levels and net upward mass flux at lower levels. This downward mass
flux comes primarily from the unsaturated
cloud-mixed convective region during the dissipation stage, and is
evaporatively driven. Unsaturated negatively buoyant cloud
mixtures dominate the buoyancy and mass fluxes in the upper portion of
all clouds while saturated positively buoyant cloud mixtures dominate
the fluxes at lower levels. Small and large clouds have distinct
vertical profiles of heating/cooling and drying/moistening, with small
clouds cooling and moistening throughout their depth, while larger
clouds cool and moisten at upper levels and heat and dry at lower
levels. The simulation results are compared to the predictions
of conceptual models commonly used in shallow cumulus parameterizations.
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reprint of the paper.
Here are some animations of the LES run used
in the analysis.
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