The near-surface velocity and potential vorticity structure of the Gulf Stream

2001 ◽  
Vol 59 (6) ◽  
pp. 949-975 ◽  
Author(s):  
T. Rossby ◽  
H.-M. Zhang
Keyword(s):  
Potential Vorticity ◽  
Gulf Stream ◽  
Surface Velocity ◽  
Near Surface ◽  
Vorticity Structure

scholarly journals Potential Vorticity Structure in the North Atlantic Western Boundary Current from Underwater Glider Observations

2016 ◽  
Vol 46 (1) ◽  
pp. 327-348 ◽  
Author(s):  
Robert E. Todd ◽  
W. Brechner Owens ◽  
Daniel L. Rudnick
Keyword(s):  
Potential Vorticity ◽  
Gulf Stream ◽  
Relative Vorticity ◽  
Western Boundary Current ◽  
Western Boundary ◽  
Loop Current ◽  
Boundary Current ◽  
Layer Potential ◽  
The North ◽  
Vorticity Structure

AbstractPotential vorticity structure in two segments of the North Atlantic’s western boundary current is examined using concurrent, high-resolution measurements of hydrography and velocity from gliders. Spray gliders occupied 40 transects across the Loop Current in the Gulf of Mexico and 11 transects across the Gulf Stream downstream of Cape Hatteras. Cross-stream distributions of the Ertel potential vorticity and its components are calculated for each transect under the assumptions that all flow is in the direction of measured vertically averaged currents and that the flow is geostrophic. Mean cross-stream distributions of hydrographic properties, potential vorticity, and alongstream velocity are calculated for both the Loop Current and the detached Gulf Stream in both depth and density coordinates. Differences between these mean transects highlight the downstream changes in western boundary current structure. As the current increases its transport downstream, upper-layer potential vorticity is generally reduced because of the combined effects of increased anticyclonic relative vorticity, reduced stratification, and increased cross-stream density gradients. The only exception is within the 20-km-wide cyclonic flank of the Gulf Stream, where intense cyclonic relative vorticity results in more positive potential vorticity than in the Loop Current. Cross-stream gradients of mean potential vorticity satisfy necessary conditions for both barotropic and baroclinic instability within the western boundary current. Instances of very low or negative potential vorticity, which predispose the flow to various overturning instabilities, are observed in individual transects across both the Loop Current and the Gulf Stream.

scholarly journals Quantifying Dispersal and Connectivity of Surface Waters Using Observational Lagrangian Measurements

2012 ◽  
Vol 29 (8) ◽  
pp. 1127-1138 ◽  
Author(s):  
Christopher G. Piecuch ◽  
Tatiana A. Rynearson
Keyword(s):  
Time Scales ◽  
Transit Time ◽  
Ocean Circulation ◽  
Time Scale ◽  
Gulf Stream ◽  
Probability Distributions ◽  
World Ocean ◽  
Surface Velocity ◽  
Near Surface ◽  
Wide Range

Abstract Probability distribution functions of displacement are central to Lagrangian statistics and the study of fluid dispersal. A method for computing marginal probability distributions of passive tracer dispersal from Lagrangian observations is developed. Using a pseudotrack approach, probability distributions for the domain of occupation and transit time are developed, complimenting more frequently used bulk statistics for average transit time and overall crossing probability. To demonstrate application of this technique to observations, likelihoods and time scales of dispersal from the Gulf Stream to the Azores are quantified using World Ocean Circulation Experiment (WOCE) Surface Velocity Program (SVP) near-surface drifter data for the years 1992–2008. Over observable time scales, the transit of a particle in the near-surface ocean from the Gulf Stream to the Azores occurs across a spectrum of time scales, from tens to hundreds of days, with an overall likelihood of 42% ± 4% and a mean time scale of 321 ± 41 days. The exclusion of measurements from drifters released after 1 January 2004 (which have been shown to potentially exhibit bias) slightly increases the overall likelihood of connection (49% ± 6%), consistent with recent surface current shifts in the northern North Atlantic, and increases the mean connection time scale (371 ± 52 days), potentially reflecting spurious acceleration of drifters in recent years. The method presented is general and applicable to a wide range of applications in physical and ecological oceanography.

scholarly journals Integrable unsteady motion with an application to ocean eddies

1998 ◽  
Vol 5 (3) ◽  
pp. 145-151
Author(s):  
A. D. Kirwan, Jr. ◽  
B. L. Lipphardt, Jr.
Keyword(s):  
Potential Vorticity ◽  
Particle Motion ◽  
Gulf Stream ◽  
Incompressible Flows ◽  
Unsteady Motion ◽  
Ring System ◽  
Time Dependent ◽  
Two Dimensional ◽  
Ocean Eddies ◽  
Multilayered Systems

Abstract. Application of the Brown-Samelson theorem, which shows that particle motion is integrable in a class of vorticity-conserving, two-dimensional incompressible flows, is extended here to a class of explicit time dependent dynamically balanced flows in multilayered systems. Particle motion for nonsteady two-dimensional flows with discontinuities in the vorticity or potential vorticity fields (modon solutions) is shown to be integrable. An example of a two-layer modon solution constrained by observations of a Gulf Stream ring system is discussed.

scholarly journals Physics-Based Relationship for Pore Pressure and Vertical Stress Monitoring Using Seismic Velocity Variations

2021 ◽  
Vol 13 (14) ◽  
pp. 2684
Author(s):  
Eldert Fokker ◽  
Elmer Ruigrok ◽  
Rhys Hawkins ◽  
Jeannot Trampert
Keyword(s):  
Pore Pressure ◽  
Seismic Velocity ◽  
Pressure Head ◽  
Groundwater Table ◽  
Surface Velocity ◽  
Seismic Velocities ◽  
Stress Monitoring ◽  
Near Surface ◽  
Velocity Variations ◽  
Velocity Changes

Previous studies examining the relationship between the groundwater table and seismic velocities have been guided by empirical relationships only. Here, we develop a physics-based model relating fluctuations in groundwater table and pore pressure with seismic velocity variations through changes in effective stress. This model justifies the use of seismic velocity variations for monitoring of the pore pressure. Using a subset of the Groningen seismic network, near-surface velocity changes are estimated over a four-year period, using passive image interferometry. The same velocity changes are predicted by applying the newly derived theory to pressure-head recordings. It is demonstrated that the theory provides a close match of the observed seismic velocity changes.

Surface-Wave Simulation for the Continuously Moving Seismic Sources

2021 ◽  
Author(s):  
Yuefeng Yan ◽  
Chengyu Sun ◽  
Tengfei Lin ◽  
Jiao Wang ◽  
Jidong Yang ◽  
...  
Keyword(s):  
Rayleigh Waves ◽  
Frequency Dispersion ◽  
Dispersion Curves ◽  
Velocity Estimation ◽  
Surface Velocity ◽  
Seismic Sources ◽  
Near Surface ◽  
Moving Source ◽  
Source Data ◽  
Doppler Effects

Abstract In exploration and earthquake seismology, most sources used in subsurface structure imaging and rock property estimation are fixed in certain positions. Continuously moving seismic sources, such as vehicles and the metro, are one kind of important passive sources in ambient noise research. Commonly, seismic data acquisition and processing for moving sources are based on the assumption of simple point passive sources, and the dispersion curve inversion is applied to constrain near-surface velocity. This workflow neglects the Doppler effects. Considering the continuously moving properties of the sources, we first derive the analytical solution for the Rayleigh waves excited by heavy vehicles and then analyze their Doppler effects and dispersion curves. We observe that the moving source data have the Doppler effect when compared with the changes in the frequency of the source intensity, but this effect does not affect the frequency dispersion of Rayleigh waves. The dispersion curves computed for moving source records are consistent with the analytical dispersion solutions, which provide a theoretical foundation for velocity estimation using moving source data.

scholarly journals Intensification of Upper-Ocean Submesoscale Turbulence through Charney Baroclinic Instability

2016 ◽  
Vol 46 (11) ◽  
pp. 3365-3384 ◽  
Author(s):  
Xavier Capet ◽  
Guillaume Roullet ◽  
Patrice Klein ◽  
Guillaume Maze
Keyword(s):  
Kinetic Energy ◽  
Gulf Stream ◽  
Energy Input ◽  
Baroclinic Instability ◽  
Upper Ocean ◽  
Mode Water ◽  
Near Surface ◽  
Turbulent Statistics ◽  
Frontal Activity ◽  
Southern Flank

AbstractThis study focuses on the description of an oceanic variant of the Charney baroclinic instability, arising from the joint presence of (i) an equatorward buoyancy gradient that extends from the surface into the ocean interior and (ii) reduced subsurface stratification, for example, as produced by wintertime convection or subduction. This study analyzes forced dissipative simulations with and without Charney baroclinic instability (C-BCI). In the former, C-BCI strengthens near-surface frontal activity with important consequences in terms of turbulent statistics: increased variance of vertical vorticity and velocity and increased vertical turbulent fluxes. Energetic consequences are explored. Despite the atypical enhancement of submesoscale activity in the simulation subjected to C-BCI, and contrary to several recent studies, the downscale energy flux at the submesoscale en route to dissipation remains modest in the flow energetic equilibration. In particular, it is modest vis à vis the global energy input to the system, the eddy kinetic energy input through conversion of available potential energy, and the classical inverse cascade of kinetic energy. Linear stability analysis suggests that the southern flank of the Gulf Stream may be conducive to oceanic Charney baroclinic instability in spring, following mode water formation and upper-ocean destratification.

AN APPROACH TO INVERSE FILTERING OF NEAR‐SURFACE LAYER EFFECTS FROM SEISMIC RECORDS

Geophysics ◽  
1961 ◽  
Vol 26 (6) ◽  
pp. 754-760 ◽  
Author(s):  
Pierre L. Goupillaud
Keyword(s):  
Surface Layer ◽  
Seismic Reflection ◽  
Normal Incidence ◽  
Resolving Power ◽  
Surface Velocity ◽  
Inverse Filtering ◽  
Near Surface ◽  
Seismic Records ◽  
Stratification Variable ◽  
Velocity Information

This paper suggests a scheme for compensating the effects that the near‐surface stratification, variable from spread to spread, produces on both the character and the timing of the seismic traces. For this purpose, accurate near‐surface velocity information is mandatory. This scheme should greatly reduce the correlation difficulties so frequently encountered in many areas. It may also be used to enhance the resolving power of the seismic reflection technique. The approach presented here is based on the rather restrictive assumptions of normal incidence, parallel equispaced plant reflectors, and noiseless conditions.

Tracking of velocity variations at depth in the presence of surface velocity fluctuations

Geophysics ◽  
2013 ◽  
Vol 78 (1) ◽  
pp. U1-U8 ◽  
Author(s):  
Benoit de Cacqueray ◽  
Philippe Roux ◽  
Michel Campillo ◽  
Stefan Catheline
Keyword(s):  
Surface Waves ◽  
Body Waves ◽  
Surface Velocity ◽  
Small Scale ◽  
Beam Forming ◽  
Near Surface ◽  
Velocity Fluctuations ◽  
Wave Separation ◽  
Double Beam ◽  
Velocity Variations

We tested a small-scale experiment that is dedicated to the study of the wave separation algorithm and to the velocity variations monitoring problem itself. It handles the case in which velocity variations at depth are hidden by near-surface velocity fluctuations. Using an acquisition system that combines an array of sources and an array of receivers, coupled with controlled velocity variations, we tested the ability of beam-forming techniques to track velocity variations separately for body waves and surface waves. After wave separation through double beam forming, the arrival time variations of the different waves were measured through the phase difference between the extracted wavelets. Finally, a method was tested to estimate near-surface velocity variations using surface waves or shallow reflection and compute a correction to isolate target velocity variations at depth.

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