[GTP] Joint GTP MMM CGD seminar at NCAR, May 10

[Silvia Gentile]

Subgrid Modelling for Geophysical Flows
Jorgen Frederiksen
CSIRO Marine and Atmospheric Research   
 


Subgrid-scale parameterisations with self similar scaling laws are 
developed for large eddy simulations (LESs) of atmospheric flows. Both 
stochastic and a deterministic representations of the effects of 
subgrid-scale eddies on the retained scales are considered. The 
stochastic subgrid model consists of a stochastic backscatter noise term 
and a drain eddy viscosity while in the deterministic subgrid model the 
net effect of these two terms is represented by a net eddy viscosity.
In both cases the subgrid transfers are calculated self consistently 
from the statistics of higher resolution reference direct numerical 
simulations (DNSs). The dependence of the subgrid parameterisations on 
the resolution of the DNSs is determined for DNSs having resolutions up 
to triangular 504 wavenumber truncations. The subgrid parameterisations 
are developed for typical large-scale atmospheric flows and for 
different strengths and spectra of kinetic energy within a 
quasi-geostrophic spectral model. LESs using the stochastic and 
deterministic subgrid parameterisations are shown to replicate the 
kinetic energy spectra of the reference DNS at the scales of the DNSs. 
It is found that the maximum strengths of the drain, net and backscatter 
viscosities satisfy scaling laws dependent on the LES truncation 
wavenumber and that the dependence of these eddy viscosities on total 
wavenumber can also be written as essentially universal functions that 
depend on flow strength and resolution. The universal scaling laws make 
the subgrid-scale parameterisations more generally applicable in LESs 
and remove the need to generate them from reference DNSs. The 
applicability of the methodology for determining subgrid-scale vertical 
velocity variations needed in cloud models is posed.



Tuesday May 10, 2011
NCAR Foothills Laboratory 3
3450 Mitchell Lane
Room 2072 MMM Conference Room
Lecture 11:30am
Refreshments 11:15 am

-- 
Silvia Gentile
NCAR IMAGe
1850 Table Mesa Drive
Boulder, CO 803035
www2.image.ucar.edu/IMAGe