scholarly journals Observing and quantifying ocean flow properties using drifters with drogues at different depths

2021 ◽  
Author(s):  
Irina I. Rypina ◽  
Timothy R. Getscher ◽  
Larry J. Pratt ◽  
Baptiste Mourre
Keyword(s):  
Vertical Velocity ◽  
Finite Size ◽  
Vertical Shear ◽  
Vertical Vorticity ◽  
Significant Term ◽  
True Model ◽  
Different Depths ◽  
Multi Level ◽  
True Values ◽  
Vorticity Balance

<p>We present analyses of drifters with drogues at 1, 10, 30 and 50 m, which were deployed in the Mediterranean Sea to investigate subduction and upwelling processes. Drifter trajectories were used to estimate divergence, vorticity, vertical velocity, and finite-size Lyapunov exponents (FTLEs), and to investigate the magnitudes of terms in the vertical vorticity equation. The divergence and vorticity are O(f) and change sign along trajectories. Vertical velocity is O(1 mm/s), is larger at depth, indicates predominant upwelling with isolated downwelling events, and sometimes changes sign between 1 and 50 m. Vortex stretching is one of, but not the only, significant term in the vertical vorticity balance. 2D FTLEs are 2x10^(-5) 1/s after 1 day, about twice larger than in a 400-m-resolution numerical model. 3D FTLEs are 50% larger than 2D FTLEs and are dominated by the vertical shear of horizontal velocity. Bootstrapping-based uncertainty for both divergence and vorticity is ~10% of the time-mean absolute values. Simulated drifters in a model suggest that drifter-based divergence and vorticity are close to true model values, except when drifters get aligned into long and narrow filaments. Drifter-based vertical velocity is close to true values in the model at 1 m but differs from the true model values at deeper depths. The errors in the vertical velocity are largely due to the lateral separation between drifters at different depths, and partially due to having drifters at only 4 depths. Overall, multi-level drifters provided useful information about the 3D flow structure.</p>

scholarly journals Observing and quantifying ocean flow properties using drifters with drogues at different depths

2021 ◽  
Author(s):  
Irina I. Rypina ◽  
Timothy R. Getscher ◽  
Lawrence J. Pratt ◽  
Baptiste Mourre
Keyword(s):  
Vertical Velocity ◽  
Finite Size ◽  
Vertical Shear ◽  
Flow Properties ◽  
Eulerian Model ◽  
Near Surface ◽  
Significant Term ◽  
Different Depths ◽  
Vorticity Balance ◽  
Vorticity Analysis

AbstractThis paper presents analyses of drifters with drogues at different depths – 1, 10, 30, 50 m – that were deployed in the Mediterranean Sea to investigate frontal subduction and upwelling. Drifter trajectories were used to estimate divergence, vorticity, vertical velocity, and finite-size Lyapunov exponents (FTLEs), and to investigate the balance of terms in the vorticity equation. The divergence and vorticity are O(f) and change sign along trajectories. Vertical velocity is O(1 mm/s), increases with depth, indicates predominant upwelling with isolated downwelling events, and sometimes changes sign between 1 and 50 m. Vortex stretching is one of, but not the only, significant term in the vorticity balance. 2D FTLEs are 2 × 10−51/s after 1 day, twice larger than in a 400-m-resolution numerical model. 3D FTLEs are 50% larger than 2D FTLEs and are dominated by the vertical shear of horizontal velocity. Bootstrapping suggests uncertainty levels of ~10% of the time-mean absolute values for divergence and vorticity. Analysis of simulated drifters in a model suggests that drifter-based estimates of divergence and vorticity are close to the Eulerian model estimates, except when drifters get aligned into long filaments. Drifter-based vertical velocity is close to the Eulerian model estimates at 1 m but differs at deeper depths. The errors in the vertical velocity are largely due to the lateral separation between drifters at different depths, and partially due to only measuring at 4 depths. Overall, this paper demonstrates how drifters, heretofore restricted to 2D near-surface observations, can be used to learn about 3D flow properties throughout the upper layer of the water column.

scholarly journals Diagnosing Mesoscale Vertical Motion from Horizontal Velocity and Density Data

2005 ◽  
Vol 35 (10) ◽  
pp. 1744-1762 ◽  
Author(s):  
Enric Pallàs Sanz ◽  
Álvaro Viúdez
Keyword(s):  
Vertical Velocity ◽  
Extreme Values ◽  
Vertical Motion ◽  
Shear Velocity ◽  
Horizontal Velocity ◽  
Vertical Shear ◽  
Coriolis Parameter ◽  
Vertical Vorticity ◽  
Omega Equation ◽  
Q Vector

Abstract The mesoscale vertical velocity is obtained by solving a generalized omega equation (ω equation) using density and horizontal velocity data from three consecutive quasi-synoptic high-resolution surveys in the Alboran Sea. The Atlantic Jet (AJ) and the northern part of the Western Alboran Gyre (WAG) were observed as a large density anticyclonic front extending down to 200–230 m. The horizontal velocity uh in the AJ reached maxima of 1.2 m s−1 for the three surveys, with extreme Rossby numbers of ζ/f ≈ −0.9 in the WAG and +0.9 in the AJ (where ζ is the vertical vorticity and f is the Coriolis parameter). The generalized ω equation includes the ageostrophic horizontal flow. It is found that the most important “forcing” term in this equation is ( fζph + ∇hϱ) · ∇2huh, where ζph is the horizontal (pseudo) vorticity and ϱ is the buoyancy. This term is related to the horizontal advection of vertical vorticity by the vertical shear velocity, uhz · ∇hζ. Extreme values of the diagnosed vertical velocity w were located at 80–100 m with max{w} ⊂ [34, 45] and min{w} ⊂ [−64, −34] m day−1. Comparison with the quasigeostrophic (QG) ω equation shows that, because of the large Rossby numbers, non-QG terms are important. The differences between w and the QG vertical velocity are mainly related to the divergence of the ageostrophic part of the total Q vector (Qh ≡ ∇huh · ∇hϱ) in the ω equation.

scholarly journals The Possible Role of Density Current Dynamics in the Generation of Low-Level Vertical Vorticity in Supercells

2017 ◽  
Vol 74 (10) ◽  
pp. 3191-3208 ◽  
Author(s):  
Adam L. Houston
Keyword(s):  
Vertical Motion ◽  
Vertical Shear ◽  
Density Current ◽  
Vertical Vorticity ◽  
Low Level ◽  
Indirect Connection ◽  
Strong Surface ◽  
Boundary Deformation ◽  
Gust Front

Abstract A physical mechanism based on density current dynamics is proposed to explain the generation of low-level vertical vorticity in supercells. This mechanism may serve as one explanation for the associative relationship between environmental low-level vertical shear and the occurrence of significant tornadoes. The mechanism proposed herein represents an indirect connection to the generation of strong surface-based rotation: the barotropic horizontal vorticity associated with the vertical shear acts to amplify existing rotation but does not directly contribute to surface rotation. The proposed mechanism couples the likelihood of a tornado to the vertical shear through the pattern of vertical motion induced through interaction of a deformed gust front and the environmental vertical shear. Results from the experiments conducted to test the veracity of the proposed mechanism illustrate that inferred patterns of tilting and vortex line orientation are consistent with the generation of positive vertical vorticity near the axis of the existing mesocyclone and negative vertical vorticity along the rear-flank gust front. Moreover, inferred tilting is found to scale with the magnitude of the environmental vertical shear, consistent with the climatologies that motivate this work. Experiments also reveal that the proposed mechanism is capable of relating boundary deformation, mesocyclone strength, and hodograph shape to the ultimate likelihood of tornadogenesis.

Experimental and numerical investigation of turbulent convection in a rotating cylinder

2009 ◽  
Vol 642 ◽  
pp. 445-476 ◽  
Author(s):  
R. P. J. KUNNEN ◽  
B. J. GEURTS ◽  
H. J. H. CLERCX
Keyword(s):  
Temperature Gradient ◽  
Boundary Layers ◽  
Power Law ◽  
Vertical Velocity ◽  
Stereoscopic Particle Image Velocimetry ◽  
Turbulent Heat Transfer ◽  
Bulk Temperature ◽  
Rossby Number ◽  
Cyclonic Vorticity ◽  
Vertical Vorticity

The effects of an axial rotation on the turbulent convective flow because of an adverse temperature gradient in a water-filled upright cylindrical vessel are investigated. Both direct numerical simulations and experiments applying stereoscopic particle image velocimetry are performed. The focus is on the gathering of turbulence statistics that describe the effects of rotation on turbulent Rayleigh–Bénard convection. Rotation is an important addition, which is relevant in many geophysical and astrophysical flow phenomena.A constant Rayleigh number (dimensionless strength of the destabilizing temperature gradient) Ra = 109 and Prandtl number (describing the diffusive fluid properties) σ = 6.4 are applied. The rotation rate, given by the convective Rossby number Ro (ratio of buoyancy and Coriolis force), takes values in the range 0.045 ≤ Ro ≤ ∞, i.e. between rotation-dominated flow and zero rotation. Generally, rotation attenuates the intensity of the turbulence and promotes the formation of slender vertical tube-like vortices rather than the global circulation cell observed without rotation. Above Ro ≈ 3 there is hardly any effect of the rotation on the flow. The root-mean-square (r.m.s.) values of vertical velocity and vertical vorticity show an increase when Ro is lowered below Ro ≈ 3, which may be an indication of the activation of the Ekman pumping mechanism in the boundary layers at the bottom and top plates. The r.m.s. fluctuations of horizontal and vertical velocity, in both experiment and simulation, decrease with decreasing Ro and show an approximate power-law behaviour of the shape Ro0.2 in the range 0.1 ≲ Ro ≲ 2. In the same Ro range the temperature r.m.s. fluctuations show an opposite trend, with an approximate negative power-law exponent Ro−0.32. In this Rossby number range the r.m.s. vorticity has hardly any dependence on Ro, apart from an increase close to the plates for Ro approaching 0.1. Below Ro ≈ 0.1 there is strong damping of turbulence by rotation, as the r.m.s. velocities and vorticities as well as the turbulent heat transfer are strongly diminished. The active Ekman boundary layers near the bottom and top plates cause a bias towards cyclonic vorticity in the flow, as is shown with probability density functions of vorticity. Rotation induces a correlation between vertical vorticity and vertical velocity close to the top and bottom plates: near the top plate downward velocity is correlated with positive/cyclonic vorticity and vice versa (close to the bottom plate upward velocity is correlated with positive vorticity), pointing to the vortical plumes. In contrast with the well-mixed mean isothermal bulk of non-rotating convection, rotation causes a mean bulk temperature gradient. The viscous boundary layers scale as the theoretical Ekman and Stewartson layers with rotation, while the thermal boundary layer is unaffected by rotation. Rotation enhances differences in local anisotropy, quantified using the invariants of the anisotropy tensor: under rotation there is strong turbulence anisotropy in the centre, while near the plates a near-isotropic state is found.

Parallax errors in cubic illuminance measurement

2020 ◽  
Vol 52 (7) ◽  
pp. 915-936
Author(s):  
RA Mangkuto ◽  
Revantino
Keyword(s):  
Reference Point ◽  
Dimensional Space ◽  
Linear Trend ◽  
Three Dimensional ◽  
Finite Size ◽  
Maximum Error ◽  
Beam Angle ◽  
Point Distance ◽  
True Values ◽  
Three Dimensional Space

The cubic illuminance concept has long been proposed to indicate light modelling in three-dimensional space. An issue relatively less discussed with regard to its measurement is the potential error due to the finite size of the cube centred at the reference point, yielding a parallax effect. In short, the measured cubic illuminance around a finite-sized object will differ from the designed values that are based on the assumption that the object is a point in space. This paper therefore aims to determine the frequency distribution of errors in estimating scalar ( Esr) and cylindrical ( Ecl) illuminances, vector to scalar illuminance ratio, and cylindrical to horizontal illuminance ratio, due to finite cube size. General uncertainty principle in measurement is employed by introducing random values of cube length and its spatial position. A linear trend is observed between cubic illuminance on the finite cube and the corresponding true values. The Esr and Ecl are approximated more accurately in the case of a point source with a small beam angle. The cube length also influences the accuracy of the results; larger cube length tends to yield less accurate estimations. To achieve maximum error of 20% in estimating Esr and Ecl for a given source–reference point distance, the cube length should not exceed 15% of such a distance.

scholarly journals Interaction of Superinertial Waves with Submesoscale Cyclonic Filaments in the North Wall of the Gulf Stream

2018 ◽  
Vol 48 (1) ◽  
pp. 81-99 ◽  
Author(s):  
Daniel B. Whitt ◽  
Leif N. Thomas ◽  
Jody M. Klymak ◽  
Craig M. Lee ◽  
Eric A. D’Asaro
Keyword(s):  
Wave Propagation ◽  
Gulf Stream ◽  
Vertical Shear ◽  
Vertical Vorticity ◽  
Shear Structures ◽  
The North ◽  
Lagrangian Observations ◽  
Critical Layers ◽  
Balanced Flow ◽  
North Wall

AbstractHigh-resolution, nearly Lagrangian observations of velocity and density made in the North Wall of the Gulf Stream reveal banded shear structures characteristic of near-inertial waves (NIWs). Here, the current follows submesoscale dynamics, with Rossby and Richardson numbers near one, and the vertical vorticity is positive. This allows for a unique analysis of the interaction of NIWs with a submesoscale current dominated by cyclonic as opposed to anticyclonic vorticity. Rotary spectra reveal that the vertical shear vector rotates primarily clockwise with depth and with time at frequencies near and above the local Coriolis frequency f. At some depths, more than half of the measured shear variance is explained by clockwise rotary motions with frequencies between f and 1.7f. The dominant superinertial frequencies are consistent with those inferred from a dispersion relation for NIWs in submesoscale currents that depends on the observed aspect ratio of the wave shear as well as the vertical vorticity, baroclinicity, and stratification of the balanced flow. These observations motivate a ray tracing calculation of superinertial wave propagation in the North Wall, where multiple filaments of strong cyclonic vorticity strongly modify wave propagation. The calculation shows that the minimum permissible frequency for inertia–gravity waves is mostly greater than the Coriolis frequency, and superinertial waves can be trapped and amplified at slantwise critical layers between cyclonic vortex filaments, providing a new plausible explanation for why the observed shear variance is dominated by superinertial waves.

On Measuring the Terms of the Turbulent Kinetic Energy Budget from an AUV

2006 ◽  
Vol 23 (7) ◽  
pp. 977-990 ◽  
Author(s):  
Louis Goodman ◽  
Edward R. Levine ◽  
Rolf G. Lueck
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Reynolds Stress ◽  
Vertical Velocity ◽  
Autonomous Underwater Vehicle ◽  
Temperature Fluctuations ◽  
Transverse Component ◽  
Vertical Flux ◽  
Vertical Shear ◽  
Statistical Uncertainty

Abstract The terms of the steady-state, homogeneous turbulent kinetic energy budgets are obtained from measurements of turbulence and fine structure from the small autonomous underwater vehicle (AUV) Remote Environmental Measuring Units (REMUS). The transverse component of Reynolds stress and the vertical flux of heat are obtained from the correlation of vertical and transverse horizontal velocity, and the correlation of vertical velocity and temperature fluctuations, respectively. The data were obtained using a turbulence package, with two shear probes, a fast-response thermistor, and three accelerometers. To obtain the vector horizontal Reynolds stress, a generalized eddy viscosity formulation is invoked. This allows the downstream component of the Reynolds stress to be related to the transverse component by the direction of the finescale vector vertical shear. The Reynolds stress and the vector vertical shear then allow an estimate of the rate of production of turbulent kinetic energy (TKE). Heat flux is obtained by correlating the vertical velocity with temperature fluctuations obtained from the FP-07 thermistor. The buoyancy flux term is estimated from the vertical flux of heat with the assumption of a constant temperature–salinity (T–S) relationship. Turbulent dissipation is obtained directly from the usage of shear probes. A multivariate correction procedure is developed to remove vehicle motion and vibration contamination from the estimates of the TKE terms. A technique is also developed to estimate the statistical uncertainty of using this estimation technique for the TKE budget terms. Within the statistical uncertainty of the estimates herein, the TKE budget on average closes for measurements taken in the weakly stratified waters at the entrance to Long Island Sound. In the strongly stratified waters of Narragansett Bay, the TKE budget closes when the buoyancy Reynolds number exceeds 20, an indicator and threshold for the initiation of turbulence in stratified conditions. A discussion is made regarding the role of the turbulent kinetic energy length scale relative to the length of the AUV in obtaining these estimates, and in the TKE budget closure.

Subsurface Imaging of Multi-Level Integrated Circuits Using Scanning Electron Acoustic Microscopy

2009 ◽  
Author(s):  
L. Meng ◽  
J.C.H. Phang ◽  
A.G. Street
Keyword(s):  
Integrated Circuits ◽  
Integrated Circuit ◽  
Modulation Frequency ◽  
Acoustic Microscopy ◽  
Subsurface Imaging ◽  
Phase Images ◽  
Different Depths ◽  
Multi Level ◽  
Electron Acoustic ◽  
Scanning Electron

Abstract The capability of the Scanning Electron Acoustic Microscopy (SEAM) technique for high resolution non-destructive subsurface imaging at different depths for a multi-level integrated circuit is assessed. Experimental results using a beveled DRAM IC sample are used to quantify the effect of the electron beam energy and modulation frequency on contrast, spatial resolution and depth of focus of SEAM amplitude and phase images.

Shear layers in a rotating fluid

1967 ◽  
Vol 29 (1) ◽  
pp. 165-175 ◽  
Author(s):  
D. James Baker
Keyword(s):  
Velocity Field ◽  
Angular Velocity ◽  
Shear Layer ◽  
Vertical Velocity ◽  
Vertical Shear ◽  
Geometrical Parameters ◽  
Homogeneous Fluid ◽  
Rotating System ◽  
Layer Flow ◽  
Good Agreement

A homogeneous fluid of viscosityvis confined between two co-axial disks (vertical separationH) which rotate relative to a rotating system (angular velocity Ω). The resulting velocity field is studied for values of the parameterv/2ΩH2in the range 1·6 × 10−2to 1·8 × 10−3. The Rossby number, defined as the ratio of the relative angular velocity of the disks to the angular velocity of the system, ranged from 0·038 to 0·0041. The dependence of the resulting velocity field (interior and boundary-layer flow) on geometrical parameters, imposed surface and bottom velocities, and Ω, is in good agreement with the calculations of Stewartson and Carrier. In particular, when the two disks rotate with the same angular velocity, the width of the vertical shear layer at the edge of the disks is found to be proportional to Ω−0·25±0·02. When the disks rotate in opposite senses, a shear layer in the vertical velocity is observed which transports fluid from one disk to the other and whose width is proportional to Ω−0·40±0·10. The magnitude and shape of the observed vertical velocity is in fair agreement with a numerical integration of the theoretical results.

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