scholarly journals Resonant Generation and Energetics of Wind-Forced Near-Inertial Motions in a Geostrophic Flow

2015 ◽  
Vol 45 (1) ◽  
pp. 181-208 ◽  
Author(s):  
Daniel B. Whitt ◽  
Leif N. Thomas
Keyword(s):  
Energy Exchange ◽  
Layer Model ◽  
Geostrophic Flow ◽  
Resonant Forcing ◽  
Isotropic Distribution ◽  
Velocity Response ◽  
Oscillatory Velocity ◽  
Resonant Generation ◽  
A Current ◽  
Shear Production

AbstractA slab mixed layer model and two-dimensional numerical simulations are used to study the generation and energetics of near-inertial oscillations in a unidirectional, laterally sheared geostrophic current forced by oscillatory winds. The vertical vorticity of the current ζg modifies the effective Coriolis frequency , which is equivalent to the local resonant forcing frequency. In addition, the resonant oscillatory velocity response is elliptical, not circular, because the oscillation periodically exchanges energy with the geostrophic flow via shear production. With damping, this energy exchange becomes permanent, but its magnitude and sign depend strongly on the angle of the oscillatory wind vector relative to the geostrophic flow. However, for a current forced by an isotropic distribution of wind directions, the response averaged over all wind angles results in a net extraction of energy from the geostrophic flow that scales as the wind work on the inertial motions times (ζg/f)2 for ζg ≪ f. For ζg ~ f, this sink of geostrophic kinetic energy preferentially damps flows with anticyclonic vorticity and thus could contribute toward shaping the positively skewed vorticity distribution observed in the upper ocean.

scholarly journals Energy Exchange between the Mesoscale Oceanic Eddies and Wind-Forced Near-Inertial Oscillations

2017 ◽  
Vol 47 (3) ◽  
pp. 721-733 ◽  
Author(s):  
Zhao Jing ◽  
Lixin Wu ◽  
Xiaohui Ma
Keyword(s):  
Energy Transfer ◽  
Energy Exchange ◽  
Kuroshio Extension ◽  
Mesoscale Eddies ◽  
Energy Transfer Efficiency ◽  
Layer Model ◽  
Strain Variance ◽  
Anticyclonic Eddies ◽  
The Kuroshio ◽  
Kuroshio Extension Region

AbstractIn this study, the energy exchange between mesoscale eddies and wind-forced near-inertial oscillations (NIOs) is theoretically analyzed using a slab mixed layer model modified by including the geostrophic flow. In the presence of strain, there is a permanent energy transfer from mesoscale eddies to NIOs forced by isotropic wind stress. The energy transfer efficiency, that is, the ratio of the energy transfer rate to the near-inertial wind work, is proportional to , where S2 is the total strain variance, is the effective Coriolis frequency, and ζ is the relative vorticity. The theories derived from the modified slab mixed layer model are verified by the realistic numerical simulation obtained from a coupled regional climate model (CRCM) configured over the North Pacific. Pronounced energy transfer from mesoscale eddies to wind-forced NIOs is localized in the Kuroshio Extension region associated with both strong near-inertial wind work and strain variance. The energy transfer efficiency in anticyclonic eddies is about twice the value in cyclonic eddies in the Kuroshio Extension region because of the influence of ζ on feff, which may contribute to shaping the dominance of cyclonic eddies than anticyclonic eddies in that region.

scholarly journals NEAR BOTTOM VELOCITIES IN WAVES WITH A CURRENT; ANALYTICAL AND NUMERICAL COMPUTATIONS

1984 ◽  
Vol 1 (19) ◽  
pp. 79 ◽  
Author(s):  
W.G.M. Van Kesteren ◽  
W.T. Bakker
Keyword(s):  
Boundary Layer ◽  
Three Dimensional ◽  
Bottom Friction ◽  
Bottom Boundary Layer ◽  
Two Dimensional ◽  
Layer Model ◽  
Bottom Boundary ◽  
Waves And Currents ◽  
A Current ◽  
Bottom Velocities

In this paper, starting from the Prandtl hypothesis a three-dimensional numerical bottom boundary layer model has been developed, which allows to calculate bottom friction by a combination of waves and currents. The model has been compared with two-dimensional analytical computations which gave similar results. The bottom friction values found are comparable to the ones, found by Lundgren (1972), however in the most relevant cases somewhat less. Furthermore in the two-dimensional case the model has been compared with measurements of Bakker and Van Doom (1978). With respect to the oscillatory motion, still some minor deviations occur between theory and measurements, due to deficiencies of the Prandtl theory.

Ocean currents measured concurrently on and off the Sydney area continental shelf

1974 ◽  
Vol 25 (3) ◽  
pp. 427 ◽  
Author(s):  
GR Cresswell
Keyword(s):  
Internal Waves ◽  
Current Speed ◽  
East Australian Current ◽  
Surface Currents ◽  
M Current ◽  
Variable Surface ◽  
Oscillatory Velocity ◽  
Counter Current ◽  
A Current ◽  
Experiment Duration

Recording current meters, a GEK, and XBT'S were used to study on and off-shelf currents for a 10 day period. Oscillatory currents with frequencies 3-8 cph were observed quite frequently at a mid-shelf mooring (depth 140 m). They were perhaps due to internal waves and were often associated with sudden increases or decreases in current speed. On two occasions the speed increases occurred when meteorological fronts passed over. The horizontal oscillatory velocity components of two of the best wave examples showed clear evidence for clockwise polarization. At the edge of the shelf (180 m), current meters 10 and 50 m above the bottom, while not showing internal waves, showed a current somewhat variable in speed (mean: 20 cm/sec; maximum 50 cm/sec), but reasonably constant in direction (northward) for the experiment duration. At this time the main southward flowing core of the East Australian Current was 120 km out from the edge of the shelf, while the region out to 50 km from the shelf contained variable surface currents. The current in the deeper water at the edge of the shelf was tentatively labelled a counter current.

Revisiting Near-Inertial Wind Work: Slab Models, Relative Stress, and Mixed Layer Deepening

2020 ◽  
Vol 50 (11) ◽  
pp. 3141-3156 ◽  
Author(s):  
Matthew H. Alford
Keyword(s):  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Wind Generation ◽  
Inertial Waves ◽  
Layer Model ◽  
Energy Increase ◽  
Layer Depth ◽  
Resonant Forcing ◽  
Relative Stress ◽  
Mixed Layers

AbstractThe wind generation of near-inertial waves is revisited through use of the Pollard–Rhines–Thompson theory, the Price–Weller–Pinkel (PWP) mixed layer model, and KPP simulations of resonant forcing by Crawford and Large. An Argo mixed layer climatology and 0.6° MERRA-2 reanalysis winds are used to compute global totals and explore hypotheses. First, slab models overestimate wind work by factors of 2–4 when the mixed layer is shallow relative to the scaling H* ≡ u*/(Nf)1/2, but are accurate for deeper mixed layers, giving overestimation of global totals by a factor of 1.23 ± 0.03 compared to PWP. Using wind stress relative to the ocean currents further reduces the wind work by an additional 13 ± 0.3%, for a global total wind work of 0.26 TW. Second, the potential energy increase ΔPE due to wind-driven mixed layer deepening is examined and compared to ΔPE computed from Argo and ERA-Interim heat flux climatology. Argo-derived ΔPE closely matches cooling, confirming that cooling sets the seasonal cycle of mixed layer depth and providing a new constraint on observational estimates of convective buoyancy flux at the mixed layer base. Locally and in fall, wind-driven deepening is comparable in importance to cooling. Globally, wind-driven ΔPE is about 11% of wind work, implying that >50% of wind work goes to turbulence and thus not into propagating inertial motions. The fraction into this “modified wind work” is imperfectly estimated in two ways, but we conclude that more research is needed into mixed layer and transition-layer physics. The power available for propagating near-inertial waves is therefore still uncertain, but appears lower than previously thought.

Resolving Crystallites in Zirconium Oxide Films

1969 ◽  
Vol 27 ◽  
pp. 140-141
Author(s):  
R.A. Ploc
Keyword(s):  
Electron Microscope ◽  
Inelastic Scattering ◽  
Zirconium Oxide ◽  
Oxide Films ◽  
Optic Axis ◽  
Objective Lens ◽  
Microscope Objective ◽  
Linear Optic ◽  
A Current ◽  
Microscope Objective Lens

The optic axis of an electron microscope objective lens is usually assumed to be straight and co-linear with the mechanical center. No reason exists to assume such perfection and, indeed, simple reasoning suggests that it is a complicated curve. A current centered objective lens with a non-linear optic axis when used in conjunction with other lenses, leads to serious image errors if the nature of the specimen is such as to produce intense inelastic scattering.

Structure of Palladium Single-Crystal Films Prepared by Flash Evaporation onto (001) NaCl Substrates

1970 ◽  
Vol 28 ◽  
pp. 456-457
Author(s):  
L. E. Murr ◽  
G. Wong
Keyword(s):  
Single Crystal ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
High Rate ◽  
Flash Evaporation ◽  
Optimum Load ◽  
Single Crystal Films ◽  
Crystal Films ◽  
A Current

Palladium single-crystal films have been prepared by Matthews in ultra-high vacuum by evaporation onto (001) NaCl substrates cleaved in-situ, and maintained at ∼ 350° C. Murr has also produced large-grained and single-crystal Pd films by high-rate evaporation onto (001) NaCl air-cleaved substrates at 350°C. In the present work, very large (∼ 3cm2), continuous single-crystal films of Pd have been prepared by flash evaporation onto air-cleaved (001) NaCl substrates at temperatures at or below 250°C. Evaporation rates estimated to be ≧ 2000 Å/sec, were obtained by effectively short-circuiting 1 mil tungsten evaporation boats in a self-regulating system which maintained an optimum load current of approximately 90 amperes; corresponding to a current density through the boat of ∼ 4 × 104 amperes/cm2.

Novel magneto-optical recording materials: Bi-substituted garnet films

1991 ◽  
Vol 49 ◽  
pp. 776-777
Author(s):  
Takao Suzuki ◽  
Hossein Nuri
Keyword(s):  
Grain Size ◽  
Amorphous Film ◽  
Nitrogen Atmosphere ◽  
Optical Recording ◽  
Garnet Film ◽  
Media Noise ◽  
Garnet Films ◽  
Order Of Magnitude ◽  
A New Technique ◽  
A Current

For future high density magneto-optical recording materials, a Bi-substituted garnet film ((BiDy)3(FeGa)5O12) is an attractive candidate since it has strong magneto-optic effect at short wavelengths less than 600 nm. The signal in read back performance at 500 nm using a garnet film can be an order of magnitude higher than a current rare earth-transition metal amorphous film. However, the granularity and surface roughness of such crystalline garnet films are the key to control for minimizing media noise.We have demonstrated a new technique to fabricate a garnet film which has much smaller grain size and smoother surfaces than those annealed in a conventional oven. This method employs a high ramp-up rate annealing (Γ = 50 ~ 100 C/s) in nitrogen atmosphere. Fig.1 shows a typical microstruture of a Bi-susbtituted garnet film deposited by r.f. sputtering and then subsequently crystallized by a rapid thermal annealing technique at Γ = 50 C/s at 650 °C for 2 min. The structure is a single phase of garnet, and a grain size is about 300A.

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