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Life Cycle of Numerically Simulated Shallow Cumulus Clouds. Part I: Transport MING ZHAO* AND PHILIP H. AUSTIN
 

Summary: Life Cycle of Numerically Simulated Shallow Cumulus Clouds. Part I: Transport
MING ZHAO* AND PHILIP H. AUSTIN
Atmospheric Science Programme, Department of Earth and Ocean Sciences, University of British Columbia, Vancouver,
British Columbia, Canada
(Manuscript received 2 June 2003, in final form 1 September 2004)
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 cumulus convection occurs in a region with
time-integrated volume roughly 2 to 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 nega-
tively 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

  

Source: Austin, Philip H. - Department of Earth and Ocean Sciences, University of British Columbia

 

Collections: Geosciences