Statistical analysis of an LES shallow cumulus cloud ensemble using a cloud tracking algorithm
Dawe, J. T.
Austin, P. H.
arxiv: Astrophysics::Galaxy Astrophysics
A technique for the tracking of individual clouds in a Large Eddy Simulation
(LES) is presented. We use this technique on an LES of a shallow cumulus cloud
field based upon the Barbados Oceanographic and Meteorological Experiment
(BOMEX) to calculate statistics of cloud height, lifetime, and other physical
properties for individual clouds in the model. We also examine the question of
nature versus nurture in shallow cumulus clouds: do properties at cloud base
determine the upper-level properties of the clouds (nature), or are cloud
properties determined by the environmental conditions they encounter (nurture).
We find that clouds which ascend through an environment that has been
pre-moistened by previous cloud activity are no more likely to reach the
inversion than clouds that ascend through a drier environment. Cloud base
thermodynamic properties are uncorrelated with upper-level cloud properties,
while mean fractional entrainment and detrainment rates display moderate
correlations with cloud properties up to the inversion. Conversely, cloud base
area correlates well with upper-level cloud area and maximum cloud height. We
conclude that cloud thermodynamic properties are primarily influenced by
entrainment and detrainment processes, cloud area and height are primarily
influenced by cloud base area, and thus nature and nurture both play roles in
the dynamics of BOMEX shallow cumulus clouds.