LANS-alpha Turbulence Parameterization
The Lagrangian-averaged Navier-Stokes-alpha (LANS-alpha) model is a
turbulence parameterization that increases eddy activity near the grid-scale.
As a post-doctoral researcher at LANL, I implemented LANS-alpha in the POP
ocean model. Simulations with LANS-alpha 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 LANS-alpha is only 30%, versus a factor of ten for doubling the
horizontal resolution.
LANS-alpha, 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 LANS-alpha shows that it increases the
eective Rossby Radius, thus allowing more eddy activity near the grid-scale
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 LANS-alpha results
Our LANS-alpha 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 LANS-alpha 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 LANS-alpha turbulence model in a primitive-equation ocean model,
J. Comp. Physics, 227, 5717
Hecht, M.W., D.D. Holm, M.R. Petersen*, B.A. Wingate:
2008,
The LANS-alpha and Leray turbulence parameterizations in primitive equation ocean modeling
J. Physics A, 41 344009
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