LANSalpha Turbulence Parameterization
The Lagrangianaveraged NavierStokesalpha (LANSalpha) model is a
turbulence parameterization that increases eddy activity near the gridscale.
As a postdoctoral researcher at LANL, I implemented LANSalpha in the POP
ocean model. Simulations with LANSalpha in an idealized channel model
domain produce turbulence statistics like a doubling of resolution, including
kinetic energy, eddy kinetic energy, and temperature proles. The cost of
adding LANSalpha is only 30%, versus a factor of ten for doubling the
horizontal resolution.
LANSalpha, which is derived using Hamilton's principle, models the
momentum equation with an extra nonlinear term and a smoothed advecting
velocity. The alpha parameter controls the strength of smoothing in a
Helmholtz inversion operator, and thus the strength of the turbulence model.
We show that ecient lters can replace the Helmholtz inversion, with similar
results.
A linear dispersion analysis of LANSalpha shows that it increases the
eective Rossby Radius, thus allowing more eddy activity near the gridscale
in low resolution ocean simulations. Preliminary simulations in a North Atlantic domain produce deeper and more realistic penetration of eddy kinetic
energy in the North Atlantic Current.
Summary of LANSalpha results
Our LANSalpha work is described in detail in the following papers:
Hecht, M.W., D.D. Holm, M.R. Petersen*, B.A. Wingate:
2008,
Implementation of the LANSalpha turbulence model in a primitive equation ocean model,
J. Comp. Physics, 227 5691
Petersen, M.R., M.W. Hecht, B.A. Wingate:
2008,
Efficient form of the LANSalpha turbulence model in a primitiveequation ocean model,
J. Comp. Physics, 227, 5717
Hecht, M.W., D.D. Holm, M.R. Petersen*, B.A. Wingate:
2008,
The LANSalpha and Leray turbulence parameterizations in primitive equation ocean modeling
J. Physics A, 41 344009

