The Euler-Poincaré Equations in Geophysical Fluid Dynamics.
Holm, D. D., J. E. Marsden and T. S. Ratiu
Large-Scale Atmosphere-Ocean Dynamics II: Geometric Methods and Models,
251-300.
J. Norbury and I. Roulstone, eds., Cambridge Univ. Press, 2002.
Abstract:
Recent theoretical work has developed the Hamilton's-principle analog
of Lie-Poisson Hamiltonian systems defined on semidirect products.
The main theoretical results are twofold:
- Euler-Poincaré equations (the Lagrangian analog of
Lie-Poisson Hamiltonian equations) are derived for a parameter
dependent Lagrangian from a general variational principle of Lagrange
d'Alembert type in which variations are constrained;
- an abstract Kelvin-Noether theorem is derived for such systems.
By imposing suitable constraints on the variations and by
using invariance properties of the Lagrangian, as one does for the
Euler equations for the rigid body and ideal fluids, we cast several
standard Eulerian models of geophysical fluid dynamics (GFD) at
various levels of approximation into Euler-Poincaré form and
discuss their corresponding Kelvin-Noether theorems and potential
vorticity conservation laws. The various levels of GFD approximation
are related by substituting a sequence of velocity decompositions and
asymptotic expansions into Hamilton's principle for the Euler
equations of a rotating stratified ideal incompressible fluid. We
emphasize that the shared properties of this sequence of approximate
ideal GFD models follow directly from their Euler-Poincaré
formulations. New modifications of the Euler-Boussinesq equations
and primitive equations are also proposed in which nonlinear
dispersion adaptively filters high wavenumbers and thereby enhances
stability and regularity without compromising either low wavenumber
behavior or geophysical balances.