Bulletin of the American Physical Society
2005 58th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 20–22, 2005; Chicago, IL
Session GN: Geophysical Flows I |
Hide Abstracts |
Chair: James Riley, University of Washington Room: Hilton Chicago PDR 2 |
Monday, November 21, 2005 10:34AM - 10:47AM |
GN.00001: The $k_h^{-5/3}$ energy spectrum in the open ocean: a new interpretation James Riley, Erik Lindborg \raggedright Previously, the kinetic and potential energy spectra in the open ocean on horizontal scales of roughly 100m to 10's of km's have usually been interpreted in terms of inertial internal gravity waves following Garrett-Munk scaling. In particular, many spectra display an approximately $k_h^{-5/3}$ dependence on the horizontal wave number $k_h$. Based upon theoretical arguments$^{1,2}$ and numerical simulations$^{1,3}$, we present an alternative interpretation. It is postulated that, under the low Froude number, high Rossby number conditions generally holding at these scales, there is a forward cascasde of energy to smaller scales, leading to local turbulent patches at scales where the local Froude number is order 1. Using Kolmogorov-like arguments, this leads to horizontal kinetic and potential energy spectra, analogous to the KOC spectra, $$ E_k(h_k) = C_1 \epsilon_k^{2/3} k_h^{-5/3} \, , \quad E_p(k_h) = C_2 \epsilon_p \epsilon_k^{-1/3} k_h^{-5/3} \, , $$ where $\epsilon_k$ and $\epsilon_p$ are the corresponding dissipation rates. Field data and theoretical arguments will be presented to support this hypothesis.\break $^1$E.Lindborg,2005,{\it Geophys.Res.Ltrs.},{\bf 32},L01809.\break $^2$E.Lindborg,2005,submitted to {\it J.Fluid Mech.}\break $^3$J.J.Riley,S.M.deBruynKops,2003,{\it Phys.Fluids},{\bf 15},2047. [Preview Abstract] |
Monday, November 21, 2005 10:47AM - 11:00AM |
GN.00002: Hamiltonian Galerkin approximations for equations of geophysical fluid dynamics Alexander Gluhovsky Arbitrary truncations in the Galerkin method commonly used to derive finite-dimensional approximations to PDEs in geophysical fluid dynamics (GFD), called the low-order models (LOMs), often result in LOMs exhibiting unphysical behavior. This can be avoided by retaining in LOMs the fundamental conservation properties of the original system through maintaining the Hamiltonian structure. Earlier, based on certain analogies between fluid dynamics and rigid body mechanics, energy-conserving LOMs in the form of coupled Volterra gyrostats were constructed for various problems in GFD (Gluhovsky and Tong, \textit{Phys. Fluids}, 1999; Tong and Gluhovsky, \textit{Phys. Rev. E}, 2002). In the talk, the development of Hamiltonian LOMs in the form of coupled gyrostats will be discussed. As examples, Hamiltonian LOMs describing 2-D and 3-D Rayleigh-B\'{e}nard convection will be considered (including the celebrated Lorenz model and its 3-D analog). The research was supported by NSF grant ATM-0413382. [Preview Abstract] |
Monday, November 21, 2005 11:00AM - 11:13AM |
GN.00003: The extra invariant for Rossby waves Alexander Balk In 1991, it was discovered that a system of Rossby waves has an extra invariant. Later, it was proved that this invariant is unique. Recently, it was found that the extra invariant implies the organization of the Rossby wave energy into zonal jets. In this talk I will show that this invariant is adiabatic. [Preview Abstract] |
Monday, November 21, 2005 11:13AM - 11:26AM |
GN.00004: Instabilities inside a precessing cylinder Patrice Meunier, Christophe Eloy The flow inside a precessing cylinder is primarily interesting because it is found inside the liquid core of the earth, where it may be responsible for the geodynamo, but also because it is found in the reservoir of rotating spacecrafts. Here, we report results of an experiment in which a cylinder rotating around its axis is mounted on a rotating turntable, with a small angle between the two axis. The flow is analyzed through sideview visualizations and PIV measurements. At low angles of precession, the flow is stable and composed of several Kelvin modes, stationnary in the frame of reference of the rotating platform. Their amplitude, accurately predicted by the linear theory, depends on the aspect ratio of the cylinder, and diverges when the height of the cylinder equals an odd number of half-wavelengths. At high angles of precession, the flow is found to destabilize, giving rise to a very turbulent motion, which can sometimes relaminarize, leading to intermittent breakdown of the flow. [Preview Abstract] |
Monday, November 21, 2005 11:26AM - 11:39AM |
GN.00005: Laboratory experiments on liquid metal spherical-Couette flows Santiago Andres Triana, Daniel Zimmerman, Doug Kelly, Daniel Lathrop We present experimental observations on liquid sodium flow in a spherical-Couette geometry. By applying an external magnetic field we are able to clearly identify at least two induced magnetic field modes with different poloidal patterns as well as different azimuthal wave numbers. The origin of many of these induced field oscillations appears to be related to inertial wave oscillations propagating in the spherical annulus. Possible implications for dynamo action and to the magneto-rotational instability will also be discussed. [Preview Abstract] |
Monday, November 21, 2005 11:39AM - 11:52AM |
GN.00006: Low magnetic Prandtl number dynamos David Montgomery, Pablo Mininni Dynamo amplification by velocity fields in conducting fluids can be highly varied. Here [1] we study dynamos numerically in one of the most efficient flows found for exciting dynamo fields at low magnetic Reynolds numbers: ``Roberts flow,'' in which the large scales are driven helically in 3D periodic boundary conditions. Three qualitatively distinct regimes are identified, depending upon mechanical Reynolds number: steady-state laminar flow, mildly unstable periodic hydrodynamic flow, and fully turbulent hydrodynamic flow. A critical magnetic Reynolds number for dynamo amplification can be identified in all three regimes, and it plateaus as the inverse magnetic Prandtl number increases (paralleling earlier results for the ``Taylor-Green vortex'' flow). It is over five times higher in the turbulent velocity field regime than it is for the time-averaged flow for that turbulent velocity field. Explorations are carried out both in the linear (``kinematic dynamo'') and nonlinear regimes of incompressible MHD. Periodic boundary conditions appear as an undesirable limitation and we are attempting to dispense with them by a spectral method in which the fields are expanded in Chandrasekhar-Kendall spherical eigenfunctions of the curl. [1] P.D. Mininni and D.C. Montgomery, ``Low magnetic Prandtl number dynamos with helical forcing,'' submitted to Phys. Rev. E (2005). Arxiv: physics/0505192. [Preview Abstract] |
Monday, November 21, 2005 11:52AM - 12:05PM |
GN.00007: Doppler Spreading of Internal Gravity Waves in the Ocean Julie Vanderhoff, James Rottman, Keiko Nomura The breaking of oceanic internal waves is an essential part of the deep-ocean mixing processes that contribute to the general circulation of the ocean, the exchange of heat and gases with the atmosphere, the distribution of nutrients and the dispersal of pollutants. The aim of this study is to improve our understanding of how these waves evolve toward dissipation and the resultant mixing of momentum, heat, and materials in a realistic ocean environment. Specifically ray and numerical simulations are used to examine the refraction of a short internal-wave packet by an inertia-wave packet to test the validity and explore the limitations of currently used models of short internal waves in the deep ocean. These so-called Doppler-spreading models for the high wavenumber end of oceanic internal wave spectra though successful are far from well understood and ignore a number of significant physical processes, especially time-dependent effects in their parameterization of dissipation. The results of our simulations are enough to show that these ignored physical effects and in particular the time dependence in the long-wave shear can make a significant difference to short-wave behavior and should be taken into account in the models. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700