Oceanic Vortices
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Abstract Turbulent Shear Flow in a Rapidly Rotating
ABSTRACT Title of dissertation: TURBULENT SHEAR FLOW IN A RAPIDLY ROTATING SPHERICAL ANNULUS Daniel S. Zimmerman, Doctor of Philosophy, 2010 Dissertation directed by: Professor Daniel P. Lathrop Department of Physics This dissertation presents experimental measurements of torque, wall shear stress, pressure, and velocity in the boundary-driven turbulent flow of water between concentric, independently rotating spheres, commonly known as spherical Couette flow. The spheres' radius ratio is 0.35, geometrically similar to that of Earth's core. The measurements are performed at unprecedented Reynolds number for this geometry, as high as fifty-six million. The role of rapid overall rotation on the turbulence is investigated. A number of different turbulent flow states are possible, selected by the Rossby number, a dimensionless measure of the differential rotation. In certain ranges of the Rossby number near state borders, bistable co-existence of states is possible. In these ranges the flow undergoes intermittent transitions between neighboring states. At fixed Rossby number, the flow properties vary with Reynolds number in a way similar to that of other turbulent flows. At most parameters investigated, the large scales of the turbulent flow are characterized by system-wide spatial and temporal correlations that co-exist with intense broadband velocity fluctuations. Some of these wave-like motions are iden- tifiable as inertial modes. All waves are consistent with slowly drifting large scale patterns of vorticity, which include Rossby waves and inertial modes as a subset. The observed waves are generally very energetic, and imply significant inhomogene- ity in the turbulent flow. Increasing rapidity of rotation as the Ekman number is lowered intensifies those waves identified as inertial modes with respect to other velocity fluctuations. -
A Laboratory Model of Exchange and Mixing Between Western Boundary Layers and Subbasin Recirculation Gyres*
1870 JOURNAL OF PHYSICAL OCEANOGRAPHY VOLUME 32 A Laboratory Model of Exchange and Mixing between Western Boundary Layers and Subbasin Recirculation Gyres* HEATHER E. DEESE,LARRY J. PRATT, AND KARL R. HELFRICH Woods Hole Oceanographic Institution, Woods Hole, Massachusetts (Manuscript received 25 January 2001, in ®nal form 8 November 2001) ABSTRACT Chaotic advection is suggested as a possible mechanism for ¯uid exchange and mixing among a western boundary current and subbasin recirculation gyres. Applications include the North Atlantic Deep Western Bound- ary Current and its adjacent mesoscale recirculation gyres. Visualization and quanti®cation of certain aspects of chaotic advection in a laboratory analog are described. Depending on the strength of the forcing, recirculating ¯uid offshore of the western boundary layer may be contained in a single gyre (not favorable for chaotic advection) or twin gyre with a ``®gure-eight'' geometry (favorable for chaotic advection). When time dependence is imposed on these steady ¯ows by varying the forcing periodically, the resulting ¯uid exchange, stirring, and mixing is most dramatic in the case of the twin gyre. A template for these processes can be formed by highlighting certain material contours (invariant manifolds) using dye and other techniques. These objects can be used to identify blobs of ¯uid (turnstile lobes) that are carried into and out of the gyres. The associated transports and ¯ushing times can be estimated. The preferential stirring and mixing in the twin-gyre case is quanti®ed by calculating the effective diffusivity of the ¯ow ®eld based on snapshots of the dye ®elds at longer times. The experiment suggests how tracers in a western boundary current might be transported into and out of neighboring recirculations and where regions of strong zonal or meridional transport might occur. -
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2250 JOURNAL OF PHYSICAL OCEANOGRAPHY VOLUME 35 Relationships between Tracer Ages and Potential Vorticity in Unsteady Wind-Driven Circulations HONG ZHANG,THOMAS W. N. HAINE, AND DARRYN W. WAUGH Department of Earth and Planetary Sciences, The Johns Hopkins University, Baltimore, Maryland (Manuscript received 4 June 2004, in final form 17 May 2005) ABSTRACT The relationships between different tracer ages and between tracer age and potential vorticity are ex- amined by simulating barotropic double-gyre circulations. The unsteady model flow crudely represents aspects of the midlatitude, middepth ocean circulation including inhomogeneous and anisotropic variability. Temporal variations range in scale from weeks to years, although the statistics are stationary. These variations have a large impact on the time-averaged tracer age fields. Transport properties of the tracer age fields that have been proved for steady flow are shown to also apply to unsteady flow and are illustrated in this circulation. Variability of tracer ages from ideal age tracer, linear, and exponential transient tracers is highly coordinated in phase and amplitude and is explained using simple theory. These relationships between different tracer ages are of practical benefit to the problem of interpreting tracer ages from the real ocean or from general circulation models. There is also a close link between temporal anomalies of tracer age and potential vorticity throughout a significant fraction of the domain. There are highly significant anticorrelations between ideal age and potential vorticity in the subtropical gyre and midbasin jet region, but correlation in the central subpolar gyre and eastern part of the domain is not significant. The existence of the relationship is insensitive to the character of the flow, the tracer sources, and the potential vorticity dynamics. -
A Steady-State Analysis of the Atlantic Ocean
REPORT UDC 551.464:551.465 CM-71 August 1987 ON INVERSE METHODS FOR COMBINING CHEMICAL AND PHYSICAL OCEANOGRAPHIC DATA: A STEADY-STATE ANALYSIS OF THE ATLANTIC OCEAN Bert Bolin, Anders Björkström, Kim Holmen and Berrien Moore Institute for the Study of Earth, Oceans and Space, University of New Hampshire, Durham, New Hampshire 03824 USA, and Laboratoire de Physique et Chimie Marines, Université Pierre et Marie Curie, Paris VI. DEPARTMENT OF METEOROLOGY <5 Ä'J> UNIVERSITY OF STOCKHOLM g ^f$f £ INTERNATIONAL METEOROLOGICAL -7, *f S> INSTITUTE IN STOCKHOLM ISSN 0280-445X DEPARTMENT OF METEOROLOGY REPORT CM-71 1 (220) UNIVERSITY OF STOCKHOLM (MISU) 1987-08-01 UDC 551.464:551.465 INTERNATIONAL METEOROLOGICAL INSTITUTE IN STOCKHOLM (IMI) Arrhenius Laboratory S-106 91 STOCKHOLM, Sweden Tel 08/16 2406 ON INVERSE METHODS FOR COMBINING CHEMICAL AND PHYSICAL OCEANOGRAPHIC DATA: A STEADY-STATE ANALYSIS OF THE ATLANTIC OCEAN by Bert Bolin, Anders Björksträn, Kim Holmen and Berrien Moore *) Abstract An attempt has been made to increase the spatial resolution in the vise of inverse methods to deduce rates of water circulation and detritus formation by the simultaneous use of tracer data and the condition of quasi-geostrophic flow. It is shown that an cverdetermined system of equations is desirable to permit analysis of the sensitivity of a solution to errors in the data fields. The method has been tested for the Atlantic Ocean, in which case we employ an 84-box model (eight layers in the vertical and 12 regions in the horizontal define the box configuration). As quasi-steady tracers we consider dissolved inorganic carbon (DIC), radiocarbon, alkalinity, phosphorus, oxygen, salinity and enthalpy.