MMM SEMINAR NCAR
The Formation of Mesoscale
Fluctuations
by Boundary Layer Convection
By means of large eddy simulations of clear and cloudy boundary layers, devoid of
explicit mesoscale forcings,
we show that buoyancy driven convection autonomously creates spatial
fluctuations with a lateral size far exceeding the boundary layer depth. If the
lateral domain is wide enough and if one waits long enough, these fluctuations
will eventually dominate the variance of nearly all (thermo) dynamic variables.
In search for the cause of this phenomenon, we determine in the simulations the
spectral decomposition of all terms contributing to the budgets of turbulence
kinetic energy and variances of the involved (thermo) dynamical variables.
These terms include the spectral transfer (cascade) and spectrally decomposed
production/dissipation and pressure-correlation terms, etc. This analysis
yields a direct insight into those processes that favor and those processes
that inhibit the formation of large scale fluctuations. We conduct the analysis
on a dry convective boundary layer and on a cloud topped boundary layer
(Sc),
and discuss the generic underlying mechanism.
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NCAR-Foothills Laboratory
Bldg 2, Rm. 1001